EPA-600/8-85-026 c.2                                          PB86-108636
              WASTEWATER TREATMENT PLANT INSTRUMENTATION
              HANDBOOK
              EMA,  Incorporated
              St. Paul, MN
              Sep 85
                            U.S. DEPARTMENT OF COMMERCE
                          National Technical Information Service
                                           NTIS

-------
                                                   EE86-1CS636
                                            EPA/600/3-85/026
                                            September 1985
WASTEWATER TREATMENT  PLANT INSTRUMENTATION  HANDBOOK
                          by

                  Robert C. Manross
                      EMA, Inc.
              St.  Paul,  Minnesota  55101
               Contract No. 68-03-3130
                   Project Officer

                   Walter W. Schuk
            Wastewater Research Division
       Water  Engineering Research Laboratory
               Cincinnati, Ohio  45268
 US. Environs r  , ~, t   .
• RcR.on \/_ , .-   ..  ' ' ••'--•ctj
       ), v •
        "1!'',-,1' ""•"'' ''"'"': 5i
        ,  iinf;o;s  60604
                                        _                  on /Agency.
                               230 ;>-,    •
       WATER  ENGINEERING RESEARCH LABORATORY
         OFFICE  OF  RESEARCH AND DEVELOPMENT
        U.S.  ENVIRONMENTAL PROTECTION AGENCY
               CINCINNATI, OHIO  45268
               REPRODUCED BY
               NATIONAL  TECHNICAL
               INFORMATION SERVICE
                  US. DEPARTMENT OF COMMERCE
                     SPRINGFIELD. VA 22161

-------
                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
    EPA/600/8-85/026
                             2.
             3. RECIPIENT'S ACCESSION NO.
               P33 6  1 0 8 o 3 S /
4. TITLE AND SUBTITLE
                Wastewater  Treatment Plant
                Instrumentation Handbook
             5. REPORT DATE
                September  1985
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
                Robert C. Manross
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                EMA, Inc.
                Control  System  Engineers
                480 Cedar  Street
                St. Paul,  MN  55391
                                                           10. PROGRAM ELEMENT NO.
             11. CONTRACT/GRANT NO.
                   68-03-3130
12. SPONSORING AGENCY NAME AND ADDRESS
                Water Engineering Research Laboratory
                Office of Research and Development
                U.S. Environmental Protection Agency
                Cincinnati, OH  45268
             13. TYPE OF REPORT AND PERIOD COVERED
                  - Final
             14. SPONSORING AGENCY CODE
                   EPA/600/14
is. SUPPLEMENTARY NOTES Project  Officer:  Walter W. Schuk   (513) 684-2621
   Prepared as a follow-up to the  Technology Transfer Wastewater  Instrumentation and
   Control Seminar, November  29  -  December 2, 1983, in Chicago, Illinois.
16. ABSTRACT

  •Instruments are  required for proper operation  of  wastewater plants.  To  be of use the
  instruments must be  operable and maintainable.  This requires care in  the  selection,-^
  application and  installation of instruments and control equipment.  Contents of the
  handbook address the "how-to" of designing and applying instrumentation  and controls
  for waste treatment  operations.  Special focus is given to problems, 'causes and
  solutions.

  The handbook covers  instruments, valves and pumps commonly used in wastewater plants.
  The material covers

   . o  Basic Theory of Operation
     o  Application
     o  Installation Requirements
     o  Maintenance and Calibration Requirements
     o  Selection  and  sizing Specifications

  The material is  intended for use by individuals with no previous background or
  specialized knowledge of instrumentation or control  equipment.  Those  responsible for
  reviewing the work done  by others, may find the designers checklist in each section a
  helpful reference.   If more technical information is required, a reference is included
17.
                                KEY WORDS AND DOCUMENT ANALYSIS    at €he end of  each section.
                  DESCRIPTORS
                                              b. IDENTIFIERS/OPEN ENDED TERMS
                           c. COSATl Field/Group
    Instrument
    Pump
    Valve
    Control
    Analytical
    Flow
    Level
    Pressure
    Measurement
18. DISTRIBUTION STATEMENT
   Release Unlimited
                                              19. SECURITY CLASS (ThisReport)
                                                 Unclassified
                           21. NO. OF PAGES
                                310
20. SECURITY CLASS (This page)
   Unclassified
EPA Form 2220-1 (R«v. 4-77)   PREVIOUS EDITION is OBSOLETE

-------
                 NOTICE






THIS  DOCUMENT  HAS BEEN  REPRODUCED FROM  THE




BEST COPY  FURNISHED  US BY THE SPONSORING




AGENCY.   ALTHOUGH  IT IS  RECOGNIZED THAT CER-




TAIN PORTIONS  ARE  ILLEGIBLE,  IT IS BEING RE-




LEASED  IN THE  INTEREST  OF  MAKING AVAILABLE




AS MUCH INFORMATION  AS  POSSIBLE.

-------
                                   DISCLAIMER
     The information in this document has been funded wholly or in part by the
United States Environmental Protec.xon Agency under Contract No. 68-03-3130 to
EMA, Inc.  It has been subject to the Agency's peer and administrative review,
and it has been approved for publication as an EPA document.  Mention of trade
names or commercial products does not constitute endorsement or recommendation
for use.
                                       ii

-------
                                   FOREWORD
     The U.S. Environmental protection Agency  is charged by Congress  with-
protecting the Nation's land, air, and water systems.  Under  a mandate  of
national environmental laws, the agency strives to formulate  and  implement
actions leading to a compatible balance between human activities  and  the
ability of natural systems to support and nurture life.  The  Clean Water
Act, the Safe Drinking Water Act, and the Toxic  Substances Control Act are
three of the major congressional laws that provide the framework  for
restoring and maintaining the integrity of our Nation's water, for
preserving and enhancing the water we drink, and for protecting the
environment from toxic substances.  These laws direct the EPA to  perform
research to define our environmental problems, measure the impacts, and
search for solutions.

     The Water Engineering Research Laboratory is that component  of EPA's
Research and Development program concerned with preventing, treating, and
managing municipal and industrial wastewater discharges; establishing
practices to control and remove contaminants from drinking water  and  to
prevent its deterioration during storage and distribution; and assessing  the
nature and controllability of releases of toxic substances to the air,
water, and land from manufacturing processes and subsequent product uses.
This publication is one of the products of tnat research and  provides a
vital communication link between the researcher and the user  community.

     This handbook was developed to provide users and designers with  a  guide
for selecting and applying instrumentation in wastewater treatment
plants.  The material is intended for use by individuals with no  previous
background or specialized knowledge of instrumentation.


                                       Francis T. Mayo, Director
                                       Water Engineering Research Laboratory
                                  iii

-------
                                    ABSTRACT
     This handbook is to be used as a guide for selecting and maintaining
instruments and final control elements in wastewater treatment plants.  Basic
applications covered include analytical measurement, flow measurement (liquid
and gas), level measurement, pressure measurement, pump control, and control
valves.

     Priority has been given to basic proven instruments that meet specific
needs and provide tangible benefits.  The material covers the theory of opera-
tion, application guidelines, installation requirements, maintenance and cali-
bration requirements, and selection*and sizing specifications.

     The handbook is intended to be used by individuals with no previous
background or specialized knowledge of instrumentation and control equipment.
A designer's checklist is provided for each of the instruments described in the
handbook.

     This report was submitted in partial fulfillment of Contract No. 68-03-
3130 by Dynamac, Inc., Rockville, Maryland, under the sponsorship of the U.S.
Environmental Protection Agency.  The report was prepared under subcontract to
EMA, Inc., St. Paul, Minnesota.  This report covers the period May 1982 to
December 1983, when work was completed.
                                       iv

-------
                                    CONTENTS


Foreword	    _x
Abstract	    *Y
Figures	
Tables   	•-.'.:
Abbreviations and Symbols	"	
Acknowledgments	
Introduction  	  	      1
     1.0  Analytical Measurement  	      3
          1.1  Total Chlorine Residual  	      3
          1.2  Dissolved Oxygen Meters  	    11
          1.3  pH	    20
          1.4  Suspended Solids   	    29
     2.0  Flow Measurement, Closed Conduit Liquid  Flow 	    40
          2.1  Magnetic Flow Meters	    40
          2.2  Sonic Flow Meters	    53
          2.3  Turbine Flow Meters	    64
          2.4  Venturi Tubes and  Flow Tubes	    71
     3.0  Flow Measurement, Closed Conduit Gas  Flow	    83
          3.1  Orifice Plate	    83
          3,.2  Venturi Tubes and  Flow Tubes	    96
          3.3  Averaging Pi trot Tubes	    105
          3.4  Turbine Flow Meters	    113
     4.0  Flow Measurement, Open  Channel	    119
          4.1  Kennison Nozzle	    119
          4.2  Palmer-Bowlus Flume 	    125
          4.3  Parshall Flume	    132
          4.4  Weir	    140
     5.0  Level Measurement	    14g
          5.1  Bubbler Level Measurement  	    14g
          5.2  Capacitance  Probe  	    155
          5.3  Float Level  Instruments  	    163
          5.4  Sonic and Ultrasonic Level Sensors   .... 	
     6.0  Pressure Measurement	
          6.'1  Pressure Cells	
          6.2  Differential Pressure  	
     7.0  Performance Testing	    JOQ
          7.1  Flow	    190
     8.0  Pump Control Methods	    2QQ
          8.1  Variable Flow  Service	   2QO
     9.0  Variable  Speed Drive  	   213
          9.1  Magnetic Coupling  	   213
          9.2  Liquid Rheostat	    „,-
          9.3  Variable Frequency  	   __
          9.4  Variable Pulley	   224
          9.5  Direct Current  (SCR)   	   227

-------
    10.0  Control Valves	   230
          10.1 Modulating Service  	   230
    11.0  Control Valve Operators  	   251
          11.1 Electric	   251
          11.2 Hydraulic	   256
          11.3 Pneumatic	   260

Appendices

     A.  Title by Subject Reference List   	   263
     B.  Reference List Sources	   272

Glossary	   276
                                       vi

-------
                                FIGURES
Number                                                              Page
1.1       Araperometric measurement 	  .....      4
1.2       Amperometric total chlorine residual analyzer   ....      5
1.3       Sample point location  	      7
1.4       Sample transport 	      S
1.5       Membrane-type DO probe cell	     12
1.6       DO meter configuration	     16
1.7       Typical pH sensor	     22
1.8       Equivalent circuit 	     22
1.9       Effect of varying asymmetric potential at   	     23
          constant (25° C) temperature
1.10      Effect of varying temperature at constant   	     23
          asymmetric potential
1.11      Flow-through pH sensor installation  	     26
1.12      Submersion pH sensor installation  	     26
1.13      Light scattering 	     31
1.14      Transraissive-type optical suspended solids  analyzer   .     31
1.15      Nuclear solids analyzer  	     33
1.16      Jackson candle turbidimeter  	     34
1.17      Forward scatter turbidimeter 	     34
1.18      Side scatter turbidimeters	     35
                                   vii

-------
                                     FIGURF-S
                                   (Continued)
Number                                                               Page



2.1       Magnetic flow meter construction  	      43

2.2       Magnetic induced voltage  	      44

2.3       Mag meter electrode snape op» Ions  	      45

2.4       Bypass pipe  installation	      43

2.5       Mag meter grounding	-.  .  .  .      49

2.6       Transmissive sonic flow meter   	      55

2.7       Reflective sonic flow meter   	      56

2.8       Transmissive sonic meter  axial configuration 	      ^Q

2.9       Turbine flow meter	      66

2.10      Turbine meter mounting  	      6g

2.11      Classic venturi tube	      72

2.12      Proprietary  flow tubes	      -^

2.13      Typical differential  piping   	      75



3.1       Concrete orifice plate  	      34

3.2       pressure profile  	      35

3.3       Orifice straight run  requirements  	      33

3.4       Steam flow installation	      90

3.5       Gas  flow installation	      91

3.6       Classic venturi tube	      96

3.7       Proprietary  flow tubes	      97

3.8       Venturi piping  requirements	      99

3.9       .Steam flow  measurement installation  diagram  .....
                                   viii

-------
                                     FIGURES
                                   (Continued)
Number                                                               Page



3.10       Gas  flow measurement  installation diagram  ......    102

3.11'      Pitot tube probe  ...................    106

3.12      Typical  up/downstream requirements ..........    103

3.13      Installation  for  steam flow  applications .......    109

3.14       Orientation   for  gas  flow  applications  .........    ng

3.15      Gas  turbine meter   ..................    114

3.16      Meter installation  ..................    116



4.1       Kennison nozzle   ...................    120

4.2       Typical  rating curve  for a 10-inch Kennison nozzle .  .    120

4.3       Palmer-Bowlus flume  .................    126

4.4       Free flow/depth relation ...............    127

4.5       Parshall flume flow element   .............    133

4.6       Head/width parameters  ................    134

4.7       Free flow submergence  ................

4.8       Sharp-crested weir  ..................

4.9       Weir shapes   .....................

4.10      Suppress rectangular  weir   ..............
 5.1       Typical  bubbler  applications .............    149

 5.2       Open  tank  bubbler  installation ............    152

 5.3       Illustration  of  probe/tank capacitive relationship . .    153

 5.4       Capacitance level  sensor  ...............    159
                                     -ix

-------
Number
5.5
5.6 '
5.7
5.8
5.9
5.10
5.11
6.1
6.2
6.3
6.4
6.5
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
FIGURES
(continued)


Counterweighted float level indicator .... 	 ..

Float switch mounting installation 	




Manifolds 	

Wet leg 	

Slider— crank stroke adjustment ....... 	



Variable speed versus throttling of centrifugal pumps ....
Two identical pumps in parallel with throttling valve ....
Page
161
1 fi?
1 £/,
1 £C
1 ^6
168

175
131
185
1S3
1S8
202
203
204
205
208
209
210
211

-------
                                    FIGURES
                                  (Continued)
Number                                                                    Page


9.1     Magnetic coupling functional block diagram  	      214

9.2     Magnetic coupling control diagram  	      216

9.3     Liquid rheostat functional block diagram  	      213

9.4     Liquid rheostat control diagram  	      220

9.5     Variable frequency functional block diagram   	      222

9.6     Simplex VFD control diagram  	      223

9.7     Variable pulley control diagram  	      226

9.8     DC drive control diagram	      229

                                                                          2^1
10.1    Ball valve 	

10.2    Butterfly valve, swing through type with flangeless   ....      233

        pipe connection

10.3    Butterfly torque 	      234

10.4    Gate valve, multi-orifice	      235

10.5    Globe valve	      236

10.6    Plug valves	      237

10.7    Traditional pressure drops for control valves  	      239

10.8    Pressure drop across a valve	      24]

10.9    Intrinsic valve characteristics  	      242

10.10   Installed valve characteristics  	      243

10.11   Installed valve gain	      244

10.12   Valve pressure drop in a pumping system	      245

10.13   Gain of a single-ported globe valve	      247


                                       xi

-------
                                    FIGURES
                                  (continued)
Number                                                                   Page


11.1    Electric operator control circuit-modulating service ....     .253

11.2    Hydraulic piston actuator  	     257

11.3    Piston actuator control circuit-incremental modulating . .  .     259

        service

11.4    Pneumatic piston actuators 	     261

1] .3    Diaphragm actuator	     262
                                      xii

-------
                                     TABLES


1.2     Recommended Application of pH Sensors 	   20

1.3     Suspended Solids Application Guidelines 	   29

2.1     Typical Applications for Mag Meters in Wastewater Treatment ...   41

2.2     Liner Selection Criteria for Specific Conditions  	   42

2.3     Transmissive Sonic Flow Meter Application Guidelines  	   53

2.4     Reflective Sonic Flow Meter Application Guidelines • 	   54

2.5     Turbine Flow Meter Application Guidelines 	   64

2.6     Venturi and Flow Tube Application Guidelines	   71

3.1     Flow Measurement, Closed Conduit Gas Flow Applications Guidelines   83

3.2     Venturi Tubes and Flow Tubes Application Guidelines 	   96

3.3     Averaging Pitot Tubes Application Guidelines  	  105

3.4     Turbine Flow Meter Application Guidelines 	  113

4.1     Flow Measurement, Open Channel Application Guidelines 	  119

4.2     Limiting Slope for Approach Piping  	  122

4.3     Maximum Line Velocity for Kennison Nozzle Installations 	  123

4.4     Palmer-Bowlus Flume Application Guidelines  	  125

4.5     Parshall Flume Application Guidelines 	  132

4.6     Submergence Limits  	  135

4.7     Wastewater Treatment Facility Application Guidelines  	  140

5.1     Bubbler Level Measurement Application Guidelines  	  148

5.2     Uncompensated Capacitance Probes Wastewater Treatment
        Facility Application Guidelines 	  155

                                      xiii

-------
                                     TABLES
                                   (continued)


 5.3     Compensated Capacitance Probes  Wastewater Treatment
         Facility Application Guidelines 	   155

 5.4     Float Level Indicators Wastewater Treatment Facility
         Application Guideline 	   163

 5.5     Sonic and Ultrasonic Level Sensors Application Guidelines ....   168

 6.1     Pressure Measurement Application Guideline	   174

 6.2     Differential Pressure Application Guideline 	   180

10.1     Comparision or Control Valves  in Wastewater Treatment Processes .   230

10.2     Cv Conversion Factors	238

10.3     Valve Characteristic Selection  Guide  	   248

11.1     Electric Valve Operators Application Guidelines 	   251
                                     xiv

-------
                         ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS

AC
cm
c
CPU
d
D
dc
DAS
DDC
DEAC
DO
P
ft/s
G
gal
gpm
H
Hz
h
hp
in.
in/s
I/O
kl/m
LCD
LED
L
Vm
Ibm
mAdc
m/s
mg/1
MHz
MUX
NEMA
ODC
Pa
psia
psig
alternating current
centimeter
centigrade
central processing unit (computer)
orifice or venturi throat diameter
pipe inside diameter
direct current
data acquisition system
direct digital control
digitally emulated analog control
dissolved oxygen
Fahrenheit
feet per second
specific gravity
gallon
gallons per minute
head
hertz
head in inches of water column     •
horsepower
inch
inches per second
input/output
kilo-liters/minute
liquid crystal display
light emitting diode
length
liters/minute
pounds mass
milliamperes direct current
meters per second
milligrams per liter
mega-hertz
multiplexer
National Electrical Manufacturer's Association
optimizing digital control
Pascals
pounds per square inch absolute
pounds per square inch gauge
R a.n If i n A
                                  XV

-------
SCADA          — supervisory control and data acquisition  system
scfh           «• standard cubic feet per hour
SCR            — silicon controlled rectifier
V              — volts
vdc            — volts direct current
VDT            — video display terminal
W              — watts
Xmtr           — transmitter
SYMBOLS

%              — percent
A              — delta or differential
p              — differential pressure
°              — degrees
>              — greater than
<              — less than
p              — specified weight
8              ~ d/D
                                   xvi

-------
                                ACKNOWLEDGMENTS
     The handbook was prepared by EMA, Inc., Control System Engineers, as
part of a technology transfer program entitled Wastewater Instrumentation
and Control Seminar.  The author acknowledges the significant contribution
made by the following EMA personnel in producing the seminar and handbook:

          Dag Knudsen
          Rich Lackman
          Claude Williams
          Cheryl Schuebel
          Roxamfe Sabean

     Helpful project guidance and assistance was provided by U.S. Environ-
mental Protection Agency personnel, Walt Schuk, Water Engineering Research
Laboratory, and Jim Smith, Center for Environmental Research Information.
Special appreciation is given to Walt Schuk for his technical review of the
handbook.  His contributions have made it a better reference manual.

     Appreciation is also expressed to the wastewater treatment plant per-
sonnel who shared their time, experiences, and opinions so the seminar and
handbook could address real-world problems and solutions.  In particular,
instrument and control support people need to be recognized for their
creativity in developing fixes, procedures, etc. for improved system per-
formance.  How greatly we would benefit if we could compile the unreported
experiences that exist in all plants.
                                     xvii

-------
                                INTRODUCTION
     Instruments are required for proper operation of wastewater treatment
plants.  Instrumentation for wastewater treatment was observed in various
states of working order during visits to wastewater treatment plants over
several years.  Personnel at these sites often criticized the instruments
for their failure to meet expectations of reliability and usefulness.
However, the same instruments performed satisfactorily in other locations.
We therefore concluded that the need was great to educate the engineering,
user, and regulatory communities about the prerequisites for success with
instrumentation.

     As part of the U.S. Environmental Protection Agency's continuing
technology transfer program, a 4-day seminar was held in November 1983 in
Chicago to teach engineers and operators how to make wastewater treatment
instruments operable and maintainable.  The program presented examples of
real-life problems and how they could be prevented.  The problems were
attributed to misapplication, incorrect installation, or improper maintenance.

     This handbook grew out of the preparation for the seminar, which
included documenting the basis for the information that was presented.

     The handbook addressed more instruments than time permitted at the
seminar, but it does not cover all instrumentation used in wastewater
treatment plants.  Priority has been given to basic, proven instruments
that meet specific needs and provide tangible benefits.  For the instruments
contained in the handbook, the material covers:

     1.  Basic theory of operation
     2.  Application
     3.  Installation requirements
     4.  Maintenance and calibration requirements
     5.  Selection and sizing specifications

The information contained here should not be considered all-inclusive;
rather, it is a beginning documentation of much-needed information on what
really works in the field.  What makes an instrument reliable and maintainable?
Many of the answeres to this question lie outside the manufacturers' manuals.
The solutions are sometimes revised procedures, test methods, or physical
modifications.  Too often this knowledge is not shared outside the treatment
plant because the persons responsible do not consider their solutions unique
or important.

-------
     When a decision is made to use an instrument for measuring a specific
parameter there is an implied commitment to maintain that instrument in an
operational state; thus, information describing the maintenance and calibration
requirements of a particular instrument are a critical part of the equipment
selection process.

     A list of technical references is included at the end of each section.
For the reader's convenience, Appendix A contains a complete list of all
references used in the handbook.  For ease in ordering, Appendix B lists
the organization, address, an
-------
1.0  ANALYTICAL MEASUREMENT


     1.1  TOTAL CHLORINE RESIDUAL

         A.   Applications

              The most common method of disinfecting wastewater plant
              effluents is chlorination.  If free chlorine gas, liquid
              hypochlorite, or chlorimines are  added to the effluent, the
              chlorine acts as an agent to destroy microscopic organisms
              that are disease producing or otherwise  objectionable.  Over
              the years criteria for rates of adding chlorine, detention
              time, and chlorine residual at the end of the detention
              period have been established.  If this criteria is adhered
              to, it is assumed the desired level of disinfection,
              elimination of harmful organisms, will be achieved.

              Chlorine residual analyzers monitor the  residual chlorine in
              an effluent stream.  This is an indirect measure.  Current
              accepted technology of monitoring chlorine  residual is based
              on.the assumption that maintaining a minimum chlorine
              residual (usually 1.0 mg/1) 30 minutes after adding chlorine
              will result in an effective disinfection level.

              If the chlorine residual drops below the desired minimum
              level, the rate of chlorine addition is  increased.
              Conversely, an increase above the minimum results in a
              decrease in the chlorine addition rate.  A  chlorine residual
              analyzer can be used to determine on-line if the correct
              chlorine dosage is being used. If corrective action, when
              indicated by the meter, is taken, then the  operation can run
              closer to the minimum level, resulting in a minimum of
              chlorine usage.

              The alternative to using a chlorine residual analyzer is to
              run tests in the laboratory.  This is not as convenient or
              timely as an on-line unit.  The on-line  analyzer provides a
              continuous reading of the chlorine residual.

         B.   Principle of Operation

              Several different measurement methods are used for chlorine
              residual, including colorometric, amperometric, and
              polarographic.  For application in wastewater, amperometric
              is the most common for Measuring  total chlorine residual.
              Therefore, discussion in this section is restricted to
              amperometric measurement.

-------
The amperometric measurement method  uses  two dissimilar
metals held in a solution or electrolyte.  A voltage is
applied to the two metals which act  as  electrodes.  Electrons
flow from the negative electrode to  the positive electrode
generating a current.  Figure 1.1 illustrates the
amperometric cell.  The amount of current flowing between the
electrodes is proportional to the amount of chlorine present
in the solution.
                   ELECTROLYTE
         I PROPORTIONAL TO Cl CONCENTRATION
     Figure 1.1.   Amperoinetric measurement.

The basic amperometric  chlorine  residual analyzer is
illustrated in Figure 1.2.   It consists of an inlet sample
tank and flow regulator,  reagent solutions with metering
pumps, measurement cell,  and electronic signal converter.
The metered sample stream acts as the electrolyte as it flows
through the measurement cell. Since chlorine in the sample
can exist in many different  chemical forms, the sample is
conditioned with  other  chemicals in order for the cell to
measure all chlorine  present in  the stream.

-------
       BUFFER
      SOLUTION
         pH4
  SAMPLE
  TANK 3
  FLOW
  REGULATOR
    SAMPLE
                                                        OUTPUT
                                                        SIGNAL
         WftSTE
          TO
         DRAIN
POTASSIUM
IODIDE
REAGENT
 WflSTE
  TO
 DRAIN
Figure 1.2.  Amperometric total chlorine residual analyzer.

      The current generated  in the measurement cell  is very
      sensitive  to  temperature variations.   A reading can change as
      much  as  3% per degree  C temperature change.  Therefore,
      automatic  temperature  compensation is necessary.  A
      temperature sensor  is  located  in the  measurement cell to
      provide  temperature feedback to the electronic converter.
      This  feedback is  then  used  to  correct the indicator and
      output signals to null-out  the temperature effects.

C.    Accuracy and  Repeatability

      The accuracy  of chlorine residual analyzers  is ^3% of full
      scale.   Several ranges are  normally available  from 0-1 mg/1
      to 0  - 20  mg/1.   The measurement error could range from
      0.03  - 0.6 mg/1 depending on the operating range used.

-------
     Repeatability of measurement on samples of equal chlorine
     concentration should be within .+1% of full scale.

     Automatic temperature compensation should enable this
     accuracy and repeatability to hold over a sample temperature
     range of 0 - 50o c  (32 - 122O F).

D.   Manufacturer's Options

     A few options are available from manufacturers of chlorine
     residual analyzers.  Some to consider are:

     1.   Local indicator in the analyzer case,

     2.   Supply of reagents,

     3.   Integral solids filter, and

     4.   Output signal for remote monitoring of the chlorine
          residual.

E.   Installation

     Chlorine residual analyzers are normally housed in free
     standing enclosures.  A sample for measurement is piped from
     the chlorine contact basin to the analyzer.  This sample
     system is a critical element for a successful analyzer
     application.  A complete installation consists of a sample
     point, sample transport, and the analyzer.

     1.   Sample point location.

          It is desirable to analyze the effluent after there is
          sufficient contact time between the chlorine and
          effluent stream for disinfection to occur.  A commonly
          accepted disinfection period is 30 minutes.  Therefore,
          it is desired to deliver a sample to the analyzer 30
          minutes after adding chlorine.  To do this, you must be
          concerned about the time in the contact tank plus the
          time to deliver a sample to the analyzer.  This is the
          total contact time as shown in Figure 1.3.

          Physically it is desired to locate the sample point so
          it does not contribute unnecessary deadtime in chlorine
          residual analysis.  In addition, take care to ensure the
          sample point is clean, thoroughly mixed, and
          representative of the monitored stream.

-------
                 TOTAL CONTACT TIME'
      CONTACT TANK TIME (T,J + SAMPLE TRANSPORT TIME (T2)
      Figure 1.3.  Sample point location.

2.    Sample transport.

     A sample line and  pump are required to deliver  the
     sample to the analyzer.  Features of this sample
     transport assembly are shown in Figure 1.4.   You should:

     a.    Select a pump capable of delivering  20  - 40 1/m
          (5 -.10 gpm).

     b.    Size the pipe for a sample velocity  of  1.5 - 3.0
          m/s (5 - 10 ft/s).

     c.    Determine the length of sample line  so  it  will
          provide the desired transport time.

     d.    Install a valve next to the analyzer so samples can
          be taken for  calibration checks on the  analyzer.

     e.    Provide a source of clean water and  required valves
          so the sample line can be backflushed to prevent
          plugging.

     f.    If solids are present, install a filter.

-------
                                     50-100 PSI
                                       CLEAN
                                       WATER
                                       SUPPUT
                           MOTOR
                        DRIVEN FILTER
                               (OPTIONAL;
X
                                           -M-
                                      SAMPLE
                                       VALVE
                                                  DRAIN
              Figure 1.4.  Sample transport.

     3.   Chlorine analyzer.

          Install the analyzer so it is easy to service and
          maintain.

          a.   Provide ample space, minimum of 1 m (3 ft), around
               all sides of the analyzer.

          b.   Locate it next to a floor drain.

          c.   Provide a table nearby with the necessary equipment
               and chemicals to perform calibration checks.

          d.   Provide a separate circuit on a lighting panel to
               power the analyzer.

F.   Designer's Checklist

     Ask the following questions when designing or reviewing
     chlorine residual analyzer applications.   All checklist
     questions should be answerable with a "yes" for  correct
     installation.

     1.   Is remote monitoring required?  If so, has  an output
          signal compatible with the receiving instrument been
          called for in the specifications?

     2.   Is a local indicator provided?

                          8

-------
     3.   Is the sample point located so that during normal plant
          flows the sum of  the contact tank time and sample
          transport time  equals 30 minutes?

     4.   Is the sample pipe length tuned to provide the required
          delivery time?

     5.   Will the sample point location be thoroughly mixed and
          representative  of the process stream?

     6.   Is the sample pump and pipe sized to provide the
          recommended  flow  rates and velocities?

     7.   Has a sample valve been provided adjacent to the
          analyzer?

     8.   Can the sample  line be backflushed?

     9.   Is there adequate space around the analyzeL for
          servicing the instrument?
G.   Maintenance and Calibration

          Task

     1. Check reagent
        supply.

     2. Check analyzer
        calibration.

     3. Check sample flow
        through  analyzer.

     4. Check reagent flow
        to sample line.

     5. Calibrate analyzer.
     6.  Replace  tubing on
        reagent  pumps.

     7.  Backflush sample
        line.

     8.  Clean analyzer
        drain lines.

     9.  Clean cell
        electrodes.
Frequency

Daily.


Daily.


Daily.


Daily.


When need is indicated by
calibration check.

Monthly.


Weekly.


Weekly.


Monthly.

-------
H.   Deficiencies

     The following  problems have been encountered in existing
     chlorine residual  analyzer installations:

     1.   The sample point does not provide a representative mixed
          sample.   This may be due to poor mixing, sample point
          location, or  contact tank design.

     2.   Contact  time  from the point of chlorine addition to the
          analyzer  is too long.

     3.   Sample lines  plug and cannot be backflushed.

     4.   No provision  for taking a sample at the analyzer for
          calibration checks.

     5.   Cramped  space around the analyzer making maintenance
          difficult.

     6.   No reagents in the analyzers.

     7.   Using reagents with the wrong concentration.

I.   References

     1.   Liptak,  B. G. and K. Venczel.  Instrument Engineers
          Handbook of  Process Measurement.  Chilton Book Company,
          Radnor,  Pennsylvania, 1969, Revised,  1982.

     2.   American Petroleum  Institute.  Manual'on Installation of
          Refinery Instruments and Control Systems.  Part II -
          Process Stream Analyzers.  API RP550, Washington, DC,
          1977, 3rd Edition.

     3.   Kulin, G. Recommended Practice for Measuring Residual
          Chlorine in Wastewater Treatment Plants with On-Line
          Analyzers. U.S. Environmental Protection Agency,
          Cincinnati, Ohio.
                           10

-------
1.2  DISSOLVED OXYGEN METERS

     A.   Applications

          Generally, dissolved oxygen (DO) meters in wastewater
          processes provide an approximate measurement of the oxygen
          available to support biological activity; in receiving
          waters, the DO meters monitor one parameter of water
          quality.

    TABLE 1.1.  DISSOLVED OXYGEN METER APPLICATION GUIDELINES

               Recommended                    Not Recommended
     Aeration tanfc                     Chlorine contact tank
     Oxygenation basins                H2S bearing streams
     Mixed liquor streams
     Secondary effluent
     Plant effluent
     Sample systems

     B.    Principles of Operation

          Commercial DO meters consist of an electrochemical cell
          (called the probe),  and a signal conditioner or
          transmitter.

          The two principal types of electrochemical cell used in DO
          probes are:

          1.   Galvanic cell.

          2.   Polarographic  cell.

          Galvanic and polarographic cells have very similar
          operating principles.   Both cells consist of an
          electrolyte and two  electrodes as shown in Figure 1.5.
                                11

-------
THERMISTOR
                                           TO SIGNAL
                                           CONDITIONER/
                                           TRANSMITTER
                                          ANODE
                                            0-RING

                                     MEMBRANE
                        ELECTROLYTE
  Figure 1.5.  Membrane type DO probe cell.
One difference is that the polarographic cell requires  a
polarizing voltage in the range of 0.5 to 1.0 vdc.
Another difference lies in selection of electrode
materials.  For example, in one proprietary probe design,
the electrodes are emersed directly in the process stream
where process fluid acts as the electrolyte.  However,  in
most commercially available probes, the electrolyte  is
contained by a gas permeable membrane, and oxygen is
brought into contact with the electrodes by the action  of
diffusion.  In either case, fluid flow past the probe
greater than 30 cm/s  (1 ft/s), is generally required to
maintain a representative sample.  Whether the probe is of
the membrane or non-membrane type, oxygen is reduced at
the cathode, where the half cell reduction reaction  is
generally:
        02 + 2H2O + 4 electrons-*4 OH"
and at the anode, the anode metal  is oxidized.   The  result
of this reduction/oxidation process is a  flow of electrons
from the cathode to the anode proportional  to the oxygen
dissolved in  the process stream.   The rate  of this
reduction/oxidation process is strongly affected by
temperature.   Therefore, accurate  temperature measurement
and compensation is essential to an accurate DO
measurement.   Temperature  is usually monitored  by a
thermistor located in the  probe, and compensation is made
in the signal conditioner/transmitter electronics.
                       1.2
                        12

-------
     Suspended and dissolved substances in the process  stream
     can also affect electron flow.  When solids accumulate  on
     the membrane, they reduce the rate of oxygen  transfer to
     the electrodes.

     A mechanical grindstone continuously polishes the  surface
     of non-membrane probes to keep the electrodes clean.  To
     maintain gas permeability, fouled membrane probes  must  be
     manually cleaned.  Certain dissolved gases interfere with
     DO measurement by either non-membrane or membrane  probes.
     Common gases to be avoided are chlorine, hydrogen  sulfide,
     carbon dioxide, and sulfur dioxide.  Chlorine will be read
     by the probe as oxygen; carbon dioxide can neutralize some
     electrolytes; and hydrogen sulfide and sulfur dioxide can
     poison some metals used for an anode.

C.   Accuracy and Repeatability

     Claims made by individual meter manufacturers for  the
     combined accuracy of the probe and signal
     conditioner/transmitter vary from _+l-3% of full scale at
     the calibration temperature.

     Additional error of +1% can be expected for each 5.0° C
     (9.0° F) of change from the calibration temperature.
     Even with temperature compensation, an additional  error  of
     3 to 4% can be expected over an operating range of 0° to
     50°C (32°-122°F).

     A combined DO measurement accuracy of +2-4% of full scale
     can be achieved in most meters under the conditions
     generally encountered at municipal wastewater treatment
     plants.  For a meter with a range of 0.0-10 mg/1 DO, this
     DO measurement accuracy represents a measurement
     uncertainty of 0.4-0.8 mg/1; however, the uncertainty
     would double (0.8-1.6 mg/1) for a meter with  a range of
     0.0-20.0 mg/1.

     The calibration of most probes will change after initial
     installation, or reinstallation after probe repair.
     Stabilization time, depending on the manufacturer, ranges
     from a couple of hours to several days.  Output readings
     must be stabilized before the accuracies above apply.

D.   Manufacturer's Options

     1.   Remote calibration unit can be installed near the
          probe to permit calibration where the transmitter  is
          not within 50 ft or is not located within sight of
          the probe.
                            13

-------
 2.    Ranges can be switch selectable; some of the more
      common range selections are:

      a.    0-3  mg/1,  0-15 rag/1.
      b.    0-5  mg/1,  0-10 mg/1, 0-20 mg/1.

 3.    Transmitter Output Signals.

      a.    4-20 mAdc  into 650 ohms  isolated.
      b.    10-50 mAdc into 250 ohms isolated.
      c.    0-5  vdc isolated.

 4.    Input power.

      a.    115  vAC, 60 Hz.

      b.    220  VAC, 60 Hz.

      c.    24 VDC

5.   Transmitter  enclosure.

     a.   Panel mounted, NEMA  IB - general  purpose.

     b.   Surface mounted, NEMA  4 - watertight.

6.   Probe mounting.

     a.   Handrail brackets.

     b.   Tank side wall brackets.

     c.   Probe holder available in lengths of 3-6 m
           (10-20  ft).

7.   Probe cable  in lengths of 7.5-15 ra  (25-50 ft).

8.   Agitator or ultrasonic cleaner for  use where fluid
     velocity across the probe is less than 30 cm/s  (1
     ft/s).

9.   High/low alarm outputs.

10.   Junction box for terminating probe  cable if the
     transmitter or remote calibration station is more
     than 10 feet from the probe connection head.
                      1.4

-------
E.   Installation

     1.   In open tanks and channels.

          In most cases, open tanks have a convenient  guard
          rail on which to mount  the probe and  transmitter  (or
          the junction box, where the  transmitter  is remote
          from the probe).  If  the guard rail is not
          conveniently located, bolt the probe  holder  brackets
          to the free board area  of the tank walls.  The probe
          holder must be rigidly  supported, but it must  also be
          readily removable for probe  maintenance  (see Figure
          1.6 for a typical configuration).  Tilt  the  probe at
          an angle away from the  general component of  process
          flow to prevent air bubbles  and debris from
          accumulating on the membrane.  Submerge  probes 60-90
          cm (2-3 ft) in an area  having sufficient agitation,
          and is representative of the process. Determine  the
          final probe location  through testing  during  startup.

     2.   In closed oxygenation tanks.

          Probe holders can be  inserted in the  process stream
          through a flanged opening in the tank cover.  The
          holder must be rigidly  fixed to the tank cover by a
          flange or quick connect sample port cover  that is
          removable for probe maintenance.  Also,  a  stilling.
          well can be installed to provide a gas seal  and a
          lateral support for an  extended probe length,   probe
          placement in the process fluid is the same as  in  open
          tanks.

          Mount the transmitter or junction box on a stand  near
          the probe.

     3.   On pipelines.

          Do not subject probes mounted on pipelines to
          pressures greater than  the manufacturer's
          recommendation, usually about 350 Pa  (50 psi). The
          selected probe must be  installed to ensure equal
          pressure on both sides  of the membrane.  Usually,
          probes are mounted in a tee  in the pipeline  with
          either a corporation  seal on the probe or  a  bypass
          line to allow removal of the probe for maintenance.
          If the probe is part  of a sample system, care  must be
          taken to have a short transport time  from the  process
          to the probe.  Where possible, direct measurement at
          the point of interest is preferable to transporting a
          sample for DO measurement.
                            15

-------
                 'SIGNAL
                  CONDITIONER
              CD
  HI/LO
 ALARMS

ISOLATED
CURRENT •
 OUTPUT
                                        5-8M
                                     •(15-23 FT)-
                                   FLEXIBLE CONDUIT
                                NOTE
                                  ~^>r~n
                                  -A1" L
                                           i	
                        , POWER
                         115 VAC 60H2
                                 RAILING OR  TANKWALL      /
                                 MOUNTING BRACKET/CLAMP -^
                                       PROBE HOLDER-
                               NOTE
                                  IF IT IS NOT POSSIBLE TO LOCATE THE SIGNAL
                                  CONDITIONER NEAR THE PROBE, INSTALL A REMOTE
                                  CALIBRATION STATION CLOSE TO THE PROBE.
                                  INSTALL RIGID CONDUIT 8. EXTEND THE  SIGNAL
                                  BETWEEN THE CALIBRATION STATION 8 THE SIGNAL
                                  CONDITIONER.  DO NOT EXCEED 120 M (4OO FT).
DETAIL A
           Figure 1.6.   DO meter configuration.
                                16

-------
P.   Designer Checklist.

     Ask the following questions when designing  or  reviewing
     dissolved oxygen meter applications.  All checklist
     questions should be answered  "yes."

     1.   If a non-membrane probe  is being considered,  is
          the process stream's conductivity  greater than  100
          micro - mhos?  Is the conductivity stable?

     2.   Are interfering dissolved gases absent (chlorine,
          hydrogen sulfide, carbon dioxide,  and  sulfur  dioxide)?

     3.   Does the process fluid wash the probe  at  a  rate
          greater than 30 cra/s (1  ft/s)?

     4.   Does mounting eliminate  the possibility of  air  bubbles
          being trapped at the measuring surface?

     5.   Does the probe see a sample representative  of the
          process?

     6.   Is the probe mounted securely without  causing likely
          collection sites for debris?

     7.   Can the probe be removed easily for inspection  or
          maintenance?

     8.   Is installation of the meter designed  so  one  person
          can calibrate it?

     9.   Is the transmitter protected from  the  weather where
          necessary?

     10.  Does the meter have automatic temperature compensation?

     11.  Is the probe installed so it is always immersed in the
          process liquid?

G.   Maintenance and Calibration

     1.  Membrane probe meters.

               Task                        Frequency

          a.  Clean membrane.     Depends on process  stream
                                  characteristics.  Some
                                  membranes must be cleaned
                                  daily; but more typically,
                                  every two days or once  a
                                  week.  Membrane breakage is a

                             17

-------
                                  common problem.  To reduce
                                  cleaning time, check
                                  calibration with a portable
                                  DO probe and clean membrane
                                  only when the two meter
                                  readings differ by more  than
                                  0.5 mg/1.

          b.  Replace membrane.   Whenever membrane breaks or
                                  when electrolyte is replaced.

          c.  Electrolyte         Every three to six months.
              replacement.

          d.  Calibration to      Every other day.
              portable probe.

          e.  Air calibration.    After membrane cleaning.

          f.  Calibration to      On initial installation or
              standard.           after major repair.

     2.  Non-membrane probe meters.

          Task                        Frequency

          a.  Inspect             Every two months.
              and clean
              grindstone.

          b.  Replace             Every six months.
              grindstone.

          c.  Calibrate to        Weekly or bi-weekly are
              standard.           typical calibration intervals.

H.   Deficiencies

     The following problems are commonly reported for dissolved
     oxygen meters.

     1.   Agitator or cleaner becomes fouled with hair or
          fibers.  Where 'possible, avoid use of agitators,
          mechanical cleaners, probe guards, or shields.

     2.   The probe becomes fouled within a few hours due to
          process stream characteristics such as grease or
          slime growth.
                          L8

-------
     3.    The probe cannot be withdrawn from the process stream
          because of mounting.

     4.    One person cannot calibrate the probe because of the
          mounting bracket, difficult alignment, or awkward
          mounting.

     5.    The probe cannot be calibrated by one person because
          the transmitter is too far from the probe and no
          remote calibration unit is installed.

     6.    The probe is placed in a "dead" area of the tank.
          Poor mixing with the rest of the tank results in a
          false signal that does not show the true state of the
          process.

I.   References

     1.    Liptak, B.G. and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement.  Chilton Book
          Company, Radnor, Pennsylvania, 1969, Revised 1982.

     2.    APWA Research Foundation.  Comparison of Field
          Testing of DO Analyzers.  Chicago, Illinois,
          September, 1982.

     3.    Kulin, G. and W.W. Schuk.  Evaluation of a Dissolved
          Oxygen Field Test protocol.  EPA 78-D-X0024-1, U.S.
          Environmental protection Agency, Cincinnati, Ohio,
          1978.

     4.    American Public Health Association, American Water
          Works Association, and Water pollution Control
          Federation.  Standard Methods For the Examination of
          Water and Wastewater; 15th Edition.  American Public
          Health Association, Washington, DC, 1980.
                           19

-------
1.3  pH

     A.   Applications

          In wastewater treatment, pH sensors are used to monitor plant
          conditions, to monitor biological treatment process
          conditions, and to control acid/base additions for pH
          adjustment.

          Regulatory agencies  require measurement of plant influent and
          effluent  pH to describe overall plant conditions.  It may
          also be necessary to monitor the pH of specific industrial
          discharges to give advance warning of possible toxic
          conditions.

          While the activated  sludge and most other biological
          processes can tolerate a variance of pH 5 "to pH 9, some—such
          as anerobic digestion—are very pH sensitive.  Normally
          monitoring of plant  influent and primary effluent or MLSS (if
          applicable) is sufficient to warn of impending toxic
          conditions.  The anerobic digestion process requires pH in
          the range 6.6 to 7.6 and will fail at pH's below 6.2.
          Because of this sensitivity/ it is important to monitor the
          pH of anerobic digester liquor.  However, because of sensor
          fouling,  continuous  monitoring of digester pH is 'not
          recommended.

          PH adjustment is required for other processes where an
          on-line pH monitor can be used.  This provides control loop
          feedback. For example, pH adjustment may be required to
          neutralize very low  pH industrial wastes, to enhance
          phosphorous removal  by alum addition or to adjust pH to
          optimum ranges for nitrification/denitrification.

          Table 1 summarizes recommended applications for continuous
          monitoring with pH sensors.

         TABLE 1.2. RECOMMENDED APPLICATION OF pH SENSORS.

     Recommended                      Not Recommended

     Plant influent                   Digesting sludge
     Primary effluent  1)
     MLSS (if applicable) 1)
     Plant effluent

     1)   In activated  sludge  plants primary effluent pH is optional if
          MLSS pH is available.

     B.   Principle of  Operation

          Commercial pH sensors all employ a glass membrane electrode
          that develops an  electrical potential varying with the pH of
          the process fluid.   A  reference electrode  is used to measure
          the potential generated across the glass electrode.

                               20

-------
Figure 1.7 shows a  typical pH sensor arrangement.  The heart
of the sensor is the glass membrane.  An electrical potential
varying with pH is  generated across the membrane.  This
potential is measured and amplified by an electronic signal
conditioner.  The complete electric circuit includes the
glass electrode wire, the glass membrane, the process fluid,
the reference electrode fill solution and finally, the
reference electrode wire.

Figure 1.8 shows an equivalent electric circuit of the pH
sensor in Figure 1.7.  Voltage at  the input of the amplifier
is:

     EI  +  Er  -  Eg  - 0

          and:

     Ei  -  Eg  -  EC

Where:

EI  =  amplifier input, mv
Eg  »  glass electrode potential,  mv
Er  -  reference electrode potential, mv

The glass electrode has the approximate characteristic:

     Eg  »  Kl  +  K2(pH)

So voltage at the amplifier input  is:

     Ei  -  Kl  +  K2(pH)  -   Er

Kl  *  asymmetric potential, mv
K2  »  electrode gain, mv/pH

The reference electrode is designed so its potential Ec is
constant with pH and other chemical characteristics of the
process fluid.  The asymmetric potential Kl varies from
sensor to sensor.  It also changes as the sensor ages.  For
this reason pH sensors must be periodically standardized
against buffer solutions of known  pH.  Figure 1.9 illustrates
the effects of varying asymmetric  potential.

The electrode gain K2 is a function of temperature. ' For this
reason most commercial pH sensors  include automatic
temperature compensation.  A temperature sensor in the
process fluid adjusts amplifier gain to compensate for
changes in electrode gain which are caused by temperature.
Figure 1.10 illustrates the effects of varying electrode
gain.
                      21

-------
                                              PREAMPLIFIER
FILL SO-
LUTION
BUFFERED
TO PH OF 7
 PROCESS
 FLUID
GLASS
ELECTRODE

— SILVER WIRE-
  W/SILVER
  CHLORIDE
  COA'ING
               "GLASS
                MEMBRANE
                                                        METER
                                      REFERENCE
                                      ELECTRODE
SATURATED  POTTASSIUM
CHLORIDE SOLUTION
                                      PROCESS
                                      FLUID
                     POROUS
               Figure 1.7.  Typical pH sensor.
                                               PREAMPLIFIER
       E  > K| 4- K2 (PH)

       ER » CONSTANT

       RQ » RESISTANCE OF GLASS ELECTRODE

       RR• RESISTANCE OF REFERENCE ELECTRODE

       RS « RESISTANCE OF PROCESS FLUID SOLUTION
              Figure 1.8.   Equivalent circuit,

                            22

-------
                                   E,.MV OFFSET DUE TO
                                   ASYMMETRIC  a REFER-
                                   ENCE POTENTIALS
                                               DESIRED
                                               RESPONSE
Figure 1.9.   Effect  of  varying asymmetric potential at
               constant (25oc) temperature.
                                   RESPONSE AT lOO^C
                        I	1	1	1	1	1	1
                                            RESPONSE AT
                                                2S«C
                                               RESPONSE AT
                                                   0«C
Figure 1.10.  Effect of varying temperature at constant
                        asymmetric potential.
                         23

-------
C.   Accuracy and Repeatability

     Manufacturer claims for pH meter accuracy range from +_0.02 pH
     units to +_0.2 pH  units.  This  represents the combined
     accuracy of  the electrodes and the signal
     conditioner/transmitter.

     Most pH meters include automatic temperature compensation.
     Temperature  effects are negligible with these meters.
     Without temperature compensation, an additional error of .002
     pH per degree centigrade difference from the calibration
     temperature  can be expected.

     The repeatability of pH meter measurements varies by
     manufacturer from 0.02 pH units to 0.04 pH units.

     Stability (drift) is an important performance parameter that
     indicates how often meters must be recalibrated.
     Manufacturer claims for stability vary from .002 pH units
     drift per week to 0.2 pH units drift per week.  Wit-li flow
     through probe mounts, the velocity of the sample oan cause a
     shift (0.2 to 0.3 pH) in measured values.

     Methods of reporting performance specifications vary among
     manufacturers. Adjustment of  the method of reporting
     performance specifications to  equal units of measure will
     show there is a large variance.in both the accuracy and the
     stability claimed by different manufacturers.  Generally, pH
     meters can achieve the following performance standards in
     wastewater treatment plants:

     Accuracy:                   +_0.1 pH
     Repeatability:              ^0.03 pH
     Stability:                  +0.02 pH/week

D.   Manufacturer Options

     Most manufacturers sell several pH probes and mounting
     assembly configurations, each  compatible with 3 or 4
     transmitter/indicator/controller units commonly called pH
     analyzers.  Probe and analyzer options are listed below.

     1.   Probe options:

          a.   Mounting configurations for in-tank submersion,
               insertion  in-process pipes, or side stream
               flow-through  installation,

          b.   Ultrasonic cleaning,

          c.   Flow-powered  cleaning,

          d.   Mechanical wiper cleaning, and

          e.   Double-junction reference electrodes.

                         24

-------
     2.    Analyzer options:

          a.   Analog or digital (LCD) indicator,

          b.   Signal outputs available:

              0-16 MA isolated
              0-20 MA isolated
              4-20 MA isolated
              0-1 VDC isolated
              0-5 VDC,

          c.   Field selectable output spans from 2-14 pH in 2 pH
              increments,

          d.   Alarm contacts; both dry contact and triac,

          e.   One manufacturer includes self-diagnosis for both
              electrodes and signal conditioner.  A failure alarm
              contact output is enclosed,

          f.   Integrated process controller.

B.   Installation

     1.    Where  pH is one parameter of a sample system.

          The best installation of a pH meter, where pH control is
          not the objective of the measurements, is as part of a
          sample system along with other on-line analytical
        '  instruments.  This locates the pH meter with other high
          maintenance instruments for ease of service.  Buffer
          solutions needed for standardization can be conveniently
          stored with other analytical instrument reagents.

          Use flow-through pH sensors in sample system
          installations.  Provide bypass and shutoff valves for
          instrument removal and service.  Select sensors with
          electrodes that are easily removed from the flow-through
          housing for cleaning and replacement.  The flow-through
          sensor should be designed so that electrode tips are
          flush  with the tube wall and do not obstruct flow.
          Locate the pH analyzer near the probe mounting assembly
          for easy standardization.  Provide work surface for
          setting containers of buffer solution during
          standardization.  Install a sample valve next to the
          sensor to collect a sample for conformance checks.
          Figure 1.11 shows sample system installation.
                         25

-------
                                            3/4 CONDUIT
        MOUNT SENSOR 8
        TRANSMITTER ON WALL
        OR SAMPLE  PANEL
                       BALL
                       VALVE
                                                   SAMPLE
                                                    FLOW
Figure  1.11.   Flow-through pH sensor installation.
                       ^FLEXIBLE  CABLE
    TRANSMITTER
     GUARDRAIL'
                               •JUNCTION  BOX
                               CONDUIT SUPPORT
                                 BRACKET
                              'PIPE CLAMP
                          ^^1" PVC CONDUIT
                              -SENSOR W/
                              INTEGRAL
                              PREAMPLIFIER
 Figure 1.12.   Submersion pH  sensor installation.

                        26

-------
2.    Submersion in open tanks and channels.

     For in-tank and open-channel installations, use a
     submersion type electrode assembly with an integral
     preamplifier.  Figure 1.12 shows a typical
     installation.  The electrode assembly is attached to a
     pvc pipe with a bracket normally mounted on a
     guardrail.  Design the bracket so that the pipe and
     electrode assembly can be removed for maintenance
     without the use of tools.  Secure all fastening devices
     to prevent dropping them in the tank or channel.  Mount
     the signal conditioner/transmitter next to the electrode
     assembly mounting bracket.  Provide enough spare cable
     to allow the sensor/pipe assembly to be lifted clear of
     the tank.

     Install a submersion probe in a well mixed zone at a
     point that will provide a representative sample of the
     process.  If the probe is installed in an open channel,
     locate it in a free flowing zone.  Design the electrode
     assembly and support pipe installation to discourage
     collection of debris.

Designer's Checklist

1.    What are the process fluid temperature and pressure?
     Can the selected probe and probe assembly handle the
     expected range?

2.    All  are wetted parts of corrosion resistant material?

3.    Can the electrode assembly and the electrodes be removed
     easily for maintenance?

4.    Is the measuring system installation designed to allow
     maintenance and calibration by one person?

5.    Are the electrodes exposed to a representative sample of
     the process fluid?

6.    Is the electrode assembly securely mounted?

7.    Is there potential for debris to hang up on the
     electrode assembly?

8.    Is the process fluid likely to coat the electrodes?

Maintenance and Calibration

     Task                        Frequency

1.  Clean electrodes.         Depends upon process fluid.
                            Once per month for plant
                            effluent.  Once per week for
                            plant influent and sludges.

-------
          Task                         Frequency

     2.  Add reference  electrode   Check weekly.  Add as necessary.
        fill fluid               (Free - flowing type electrode)

     3.  Replace reference         As dictated by operating
        electrode                experience.
                                 (Non flowing gel type electrode)

     4.  Standardization.          Check once per 'week after
                                 initial installation.  Reduce to
                                 once per month if justified by
                                 experience.

     5.  Transmitter  calibration.  Check once per 6 months.

H.   Deficiencies

     The following problems are commonly reported for pH meters:

     1.    Electrodes become coated with grease or sludge.
          Mechanical wipers have  demonstrated some success in
          sewage treatment applications.  Ultrasonic cleaners do
          not work on  soft coatings like grease, oil, and
          sludges.  The best  solution to coating is periodic
          cleaning by  trained personnel.

     2.    Plugging of  reference electrode.  Switch to a double
          junction reference  electrode when plugging is a problem.

     3.    No provision for easy removal of probes for cleaning or
          replacement.  Probes should be removable without
          shutting down process piping.

     4.    The pH meter can't  be easily calibrated or standardized
          because the  transmitter/indicator is too far away from
          the probe.

I.   References

     1.    Liptak, B. G. and K. Venczel.  Instrument Engineers
          Handbook of  Process Measurement.  Chilton Book Company,
          Radnor, Pennsylvania, 1969, Rev. 1982.

     2.    Consdidine,  D. M. ed.   Process Instruments and Controls
          Handbook.  McGraw Hill, New York,  1974.
                                          /
     3.    Krigman, A.   Guide  to Selecting  pH and ORP
          Instrumentation.   InTech, August,  1982, p. 31.
                           28

-------
1.4  SUSPENDED SOLIDS
     A.    Application
          Suspended solids analyzers are used in wastewater treatment
          plants  to continuously measure the concentration of solids in
          various process streams.  Concentrations of interest range
          from effluent  quality, 10-30 mg/1, to thickened sludge of
          several percent solids.  A variety of instruments are
          commercially available to accommodate this wide spectrum of
          concentrations.  This section of the handbook will review
          light emitting and nuclear type solids analyzers.
        TABLE 1.3.  SUSPENDED SOLIDS APPLICATION GUIDELINES
     Recommended
Optical Analyzers

             Not Recommended
     Solids concentrations  from
       20 mg/1 -  8%
     Return activated sludge
     Waste activated  sludge
     Mixed liquor
     Plant effluent
     Gravity thickened sludge
     Centrifuge supernatant
             Primary solids
             Flotation thickened sludge
             Solids concentration
               greater than 8%
                         Nuclear Analyzers
     Recommended
     Thickened sludge with
       concentrations greater than
       8%
     Centrifuged  sludge
             Not Recommended

             Streams with solids
               concentrations less than 15%
             Streams with entrained air
               bubbles
             Line sizes larger than 35 cm
               (14 in.)
             Line size smaller than 15 cm
               (5 in.)
                               29

-------
                            Ultra-sonic Analyzers
          Recommended

(Note 1)   Solids concentration from
            1-8% solids
          Primary sludge
          Waste activated  sludge
          Return activated sludge
          Gravity thickened sludge
Not Recommended

Mixed liquor
Secondary effluent
Plant effluent
Pipe sizes greater than 30 cm
  (12 in.)
Pipe sizes less than 10 cm
  (4 in.)
Notes:

1.   Ultrasonic analyzers are not described in this section but they are
     commercially available for measuring suspended solids^
          B.    Principle of Operation

               Commonly used suspended solids instruments are based on the
               attentuation or scattering of a beam of radiation.   The type
               of  beam used can be light, ultrasound or nuclear.   This
               section will address those instruments which use light or
               nuclear radiation.

               1.    Optical technique.

                    Optical techniques for measuring suspended solids are
                    based  on scattering of a beam of light by the  suspended
                    particles (see Figure 1.13).  The portion of the light
                    scattered is a function of the number and size of
                    particles.  Light transmitted through the stream is
                    reduced in proportion to the light that is scattered;
                    therefore, an instrument which can measure the scattered
                    light, transmitted light or both, provides a measure of
                    the suspended solids present.

                    The optical type of suspended solids analyzer  consists
                    of a lamp which acts as a source of light and  a
                    photocell which measures the transmitted or scattered
                    light  (see Figure 1.14).  Arrangement of the lamps and
                    photocells depends on the manufacturer.  An electronic'.
                    package analyzes the received light and correlates this
                    to the suspended solids in the sampled stream.
                                    30

-------
        LENS
     LIGHT
    SOURCE
                                              SCATTERED
                                            4 LIGHT RAY
                                                      TRANSMITTED
                                                      LIGHT RAY
                  Figure  1.13.  Light scattering.
    LIGHT
    SOURCE
   SIGNAL
     TO
TRANSMITTER
Figure 1.14.   Transmissive type  optical suspended  solids analyzer.

                                31

-------
     Since  solids buildup and coating is a problem in
     wastewater plants, manufacturers have devised several
     different methods to minimize or eliminate the effects
     of  solids buildup.  One technique uses a small sample
     chamber  in which a piston draws and dispels a sample.
     The piston is designed with a flexible edge that
     mechanically cleans the glass which separates the lamp
     and photocell from the sample.  Another design uses
     multiple lamps and photocells.  By measuring the
     transmitted light at different angles to the lamp,
     comparisons can be made to null the effect of solids
     buildup.  Still another design measures the light
     reflected at an angle to a falling stream, because  the
     sample does not contact the lens, solids buildup does
     not occur.

2.    Nuclear  radiation.

     A nuclear density gauge is a non-contact measurement of
     solids density.  It does not measure percent solids
     directly.  But rather it measures the specific gravity
     of  the material.  If the specific gravity of the liquid
     and solids is constant, then a correlation can be made
     between  measured specific gravity and percent solids
     concentration.

     In  operation, a radioactive source emits gamma rays
     which  are absorbed by material in the measured stream.
     High density materials absorb more radiation than low
     density  materials.  Thus a nuclear gauge averages the
     density  of all material in the stream.  The detector
     senses the total radiation passing through the stream to
     determine the material density.  Figure 1.15 shows  a
     solids analyzer.

3.    Turbidity.

     Turbidity can be classified as forward scatter or side
     scatter  measurement types.  In forward scatter
     turbidimeters, the measurement is in Jackson Turbidity
     Units  (JTO).  The JTU unit was derived from the Jackson
     candle turbidimeter shown in Figure 1.16.  In this
     instrument, the sample is poured into the glass tube
     until  the candle flame is seen to disappear, leaving a
     uniform  field of light.  At this transition point,  the
     height of the column is read and converted into JTU's
     from a standard table.
                     32

-------
                 LEAD  SHIELDING
                     RADIATION  SOURCE
                       MEASURED  PRODUCT
                       PIPE  CLAMP
                       RADIATION
                       DETECTOR
                             TO
                             TRANSMITTER
Figure 1.15.  Nuclear  solids analyzer.
                 33

-------
                           JJ M:
       Figure 1.16.  Jackson candle turbidimeter.

         Figure 1.17 shows a forward scattering  type
         turbidimeter.   This instrument measures the amount of
         light scattered by particles in  the  forward direction
         from the light beam.  By establishing and maintaining a
         ratio of scattered light to the  transmitted light, the
         effects of color changes can be  eliminated and a direct
         measurement made of the particulates.
 LIGHT
SOURCE
       Figure 1.17.   Forward scatter turbidimeter.

                          34

-------
     In side scatter turbidimeters,  the  turbidity is
     determined by measuring the amount  of  light scattered at
     some angle (usually 9QO) from the light path by
     particles suspended in the sample.   Figure 1.18
     illustrates two styles of turbidimeters which use the
     side scatter method of measurement.
LIGHT
SOURCE
         LENS
                               PHOTOCELL
                LIGHT SCATTER
                                LENS
                      PHOTOCELL
                                         LIGHT
                                          S°URCE
                     \
                      '
              TURBID
              SAMPLE
                      .
                      ^  I / ',"
                             '
TURBID
 METER
  BODY
                                      SAMPLE
                                     OVERFLOW
                                     TO DRAIN
                          SAMPLE
                          DRAIN
                    SAMPLE
                    INLET
                SURFACE SCATTER
   Figure  1.18.   Side scatter turbidimeters.
                      3.S

-------
          The units for side scatter turbidimeters are
          Nephelometric Turbidity Units (NTU).  The word
          "nephelometric" describes the optical technique of
          measuring scattered light at an angle to the light path.

          Formazin polymer has gained acceptance as the turbidity
          reference suspension standard.  It is easy to prepare
          and is  reproducible in its light scattering properties.
          Although a  sample of formazin suspension measured by
          forward scatter (JTU's) and side scatter (NTU's)
          turbidimeters will read approximately the same, they are
          not identical.  A poor correlation exists when measuring
          a wastewater sample because of the variation in the
          absorption  and optical scattering properties of the
          suspended particles.  Because of this, turbidity units
          are not interchangeable between different types of
          turbidity meters.  JTU or NTU can be correlated to
          suspended solids for a specific application.

C.   Accuracy and Repeatability

     1.   Optical solids analyzers.

          The accuracy of a suspended solids analyzer is typically
          +5% of  full scale.  Several ranges of operation are
          available.  On a range of 0-3000 mg/1, the instrument
          error is +_150 mg/1 of the actual reading.  For a 0-10%
          range the error would be _+0.5%.

          The repeatability is not readily available from the
          manufacturer's literature.  However ^1% of full scale is
          a reasonable estimate of the repeatability.

     2.   Nuclear solids analyzers.

          Nuclear gauges offer accuracy of +_0.05% of full scale.
          However, since the instrument measures specific gravity
          and is empirically calibrated to read out in percent
          solids the  accuracy of solids measurement can be
          affected by changes in the specific gravity of the
          particulate or the fluid.

     3.   Turbidity analyzers.

          Turbidity is a relative measurement.  For this reason it
          is inappropriate to apply conventional standards of
          accuracy to this measurement.  For purposes of this
          discussion, consider turbidimeter accuracy, _+5% of full
          scale and repeatability j^2% of full scale.

D.   Manufacturer's Options

     Some options are common to all types of solids analyzers.
     These common options are listed first followed by options
     which apply to a specific analyzer type.

                     	36 .. _

-------
1.   Common options.

     a.    Low and high alarm contact outputs.

     b.    Voltage or  current output signals for remote
          monitoring.   This is  a standard offering on some
          analyzers.

     c.    Wall or panel mounting for the transmitter
          enclosure.

     d.    Length of interconnecting cable between the sensor
          and transmitter.

2.   Optical analyzers.

     a.    Light shields to prevent stray light from
          introducing  measurement errors.

     b.    In-line pipe mounting adapters.

     c.    Mounting brackets for installing on hand rails.

     d.    Length or style (depends on manufacturer) of the
          sensor probe.

     e.    Test standards for troubleshooting and calibration
          of transmitter electronics.

3.   Nuclear analyzers.

     a.    Mass flow computer (requires flowmeter input).

     b.    Pipe spool pieces with cleanout ports.

     c.    Radiation source decay compensation.

     d.    Automatic temperature compensation.

4.   Turbidity analyzers.

     a.    Sample system accessories such as pumps and bubble
          traps.

     b.    Installation Kits.

     c.    Extended high ranges.

     d.    Test standards for calibration.
                     37

-------
E.   Installation

     Installation details for solids analyzers are unique to each
     manufacturer.   The variations of installation are too
     numerous to list here.  Manufacturers installation manuals
     should be obtained and used when designing for a solids
     analyzer installation.  Some general considerations for
     installing solids analyzers follow:

     1.    Solids analyzers require frequent attention and
          calibration checks.  Provide space for servicing and
          locate the sensor so it can be easily reached.

     2.    If sample  lines are required, make sure they are large
          enough and that flow velocity is high enough to minimize
          line plugging.

     3.    Provide flushing water for the instrument and sample
          valve.

     4.    Provide a  sample valve next to the sensor so samples can
          be taken to check analyzer calibration.

     5.    Mount the  transmitter within sight of the sensor.

     6.    Locate sensors or sample line taps where air bubbles are
          least likely to be present.  Preferably a vertical line
          with an up-»flow.

P.   Designer's Checklist

     The designer is referred to the manufacturer's installation
     instructions or operation and maintenance manuals for details
     of  analyzer installation.  Also review the general
     installation suggestions contained in Part E of this
     section.  Caution:  the performance of solids analyzers is
     directly related to ease of maintenance and calibration.

G.   Maintenance and Calibration

     Refer to the manufacturer's operation and maintenance manuals
     for specific reconunendations on frequency of tasks.  The
     following are general maintenance considerations for all
     suspended solids and turbidity analyzers.

          Task                        Frequency

     1.  Check analyzer                 Weekly.
        calibration.

     2.  If sample line is used,        Daily.
        check sample and drain
        flows.

                          33

-------
          Task                        Frequency

     3. .If sample line  is  used,        Weekly.
        backflush sample line.

     4. Calibrate analyzer with        When need is indicated by
        a solution of known            a conformance check.
        solids concentration.

H.   Deficiencies

     Some problems encountered in existing solids analyzer
     installations are  described below.

     1.   The solids analyzer or the sample line tap is not
          located where there is a well mixed representative
          process sample.

          a.    Air bubbles in the sample.

     2.   No provision  for taking a sample at the analyzer for
          calibration checks.

     3.   Locating the  sensor and/or transmitter so servicing and
          maintenance are  difficult due to inaccessibility.

     4.   Analyzer operating range does not match the range of
          solids in the process.

     5.   For optical and  turbidity analyzers, stray light causes
          erroneous readings.

I.   References

     1.   Standard Methods for the Examination of Water and
          Wastewater.   American Public Health Association,
          American Water Works Association, Water Pollution
          Control Federation, Washington, DC, 1975, 14th edition.

     2.   Condrashoff,  G.  Wastewater In-Line Turbidity and
          Suspended Solids Measurements.  Monitor Technology,
          Inc., Redwood City, CA.

     3.   Simms,  R. J.  A  Return to Accurate Turbidity
          Measurement.  Monitor Technology, Inc., Redwood City,  CA.

     4.   Liptak,  a. G. and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement, Chilton Book Company,
          Radnor,  PA, 1969, Revised, 1982.
                          39

-------
2.0  FLOW MEASUREMENT,  CLOSED CONDUIT LIQUID FLOW


     2.1  MAGNETIC FLOW METERS

          A.    Applications

               1.    Operating conditions where magnetic flow meters (mag
                    meters) are suitable include:

                    a.    Streams in which head losses must be minimized.

                    b.    Liquids with a conductivity greater than 5 micro-mhos
                         per centimeter.

                    c.    Corrosive and/or abrasive process streams.

                    d.    Liquid streams with a solids concentration less than
                         10% by weight.

               2.    Mag meters are not recommended for the following
                    applications:

                    a.    Non-conducting liquid process streams.

                    b.    Gas streams.

                    c.    Streams with powdered or granular dry chemicals.

                    d.    Liquid streams with a solids concentration greater
                         than 10% by weight.
                                     40

-------
TABLE 2.1.  TYPICAL APPLICATIONS FOR MAG METERS IN WASTEWATER TREATMENT
    Service
Liner Material
Raw Sewage

Settled  Sewage

Primary  Sludge

Mixed  Liquor

Return Activated
Sludge
Waste  Activated
Sludge
Thickened Sludge
Digester Sludge
Digester Supernatant
Polymer  Solutions
Polyurethane
Clean  (Process)
Water
Strongly Corrosive
 Polyurethane

 Polyurethane

 Polyurethane
 or Teflon
 Polyurethane

 Polyurethane

 Polyurethane

 Polyurethane or Teflon
 Polyurethane or Teflon
 Polyurethane or Teflon
 Teflon, Rubber,
 Rubber
 Polyurethane, Rubber

 Teflon or Kynar
Gasket Material

Asbestos, Rubber,
Neoprene
Asbestos, Rubber,
Neoprene
Teflon/Asbestos

Asbestos, Rubber,
Neoprene
Asbestos, Rubber,
Neoprene
Asbestos, Rubber,
Neoprene
Teflon/Asbestos
Teflon/Asbestos
Teflon/Asbestos
Teflon/Asbestos,

Rubber, Neoprene

Teflon/Asbestos
                                 41

-------
             TABLE  2.2.   LINER SELECTION CRITERIA FOR SPECIFIC CONDITIONS
                 Resistance to Abrasion
Liner Material

Teflon

Kynar

Polyurethane

Butyl rubber

Neoprene
  (Mild)
(Severe)
Good        Not Recom.

Good        Not Recom.

Excellent   Excellent

Excellent   Good

Excellent   Good
  Resistance to
    Corrosion

Excellent

Excellent

Not Recommended

Not Recommended

Not Recommende^
  Maximum
Temperature

150°C (300°F)

100°C (212°F)

 88°C (190°F)

 71°C (160°F)

 93°C (200°F)
               4.   Cost considerations regarding liner materials.

                    If a base price is assumed for a polyurethane liner,  the
                    following costs may be used for comparison:

                    a.   Rubber or neoprene costs will be approximately
                         $5.90/cm  ($15.00/in) of meter diameter, greater
                         than an equivalent meter with a polyurethane  liner.

                    b.,   Teflon costs will be approximately  $87.00/cm
                         ($220.00/in) of meter diameter, greater than  an
                         equivalent meter with a polyurethane  liner.

          B.   Principle of Operation

               Magnetic flow meters  (mag meters) operate by  using Faraday's
               principle of electro-magnetic induction in which the  induced
               voltage generated by an electrical' conductor  moving  through a
               magnetic field is proportional to the conductor's velocity.
               Figures 2.1 and 2.2 illustrate the application  of this
               principle to volumetric flow rate measurements  of wastewater
               treatment process streams.

               Commercial power is applied to the meter, and the coil  driver
               energizes the magnetic coils which encase the spool  pipe,
               creating a magnetic field.  If the process liquid has enough
               conductivity, it will act as an electrical conductor  and will
               induce an electrical voltage.  This voltage io  a summation of
               all the incremental voltages developed within each liquid
               particle occupying the magnetic field and is  proportional  to
               the field strength, pipe diameter, and "conductor velocity."
               The more rapid the rate of liquid flow, the greater  the
               instantaneous value of electrode voltage.
                                    42

-------
The induced voltage  is  received  by  the  two  electrodes mounted
180° apart in the meter.  This signal is  sent  to  the
converter/transmitter where it is summed, referenced, and
converted from a magnetically induced voltage  to  the
appropriate scaled output.  The  output  signal  then goes to any
of the appropriate operating interfaces,  e.g.,  a  control panel
indicating meter, a  control system  computer, etc.

Two basic types of mag meters are available, the  AC mag meter
and the dc mag meter.  With the  AC  mag, line voltage is applied
to the coils and a continuous flux  is created  producing a
continuous low level AC electrode voltage.  With  the dc mag
meter, the magnetic  coils are periodically  energized, thereby
producing two induced electrode  voltages  — one when energized,
the other when de-energized.  The energized electrode voltage
is a combination of  both true signal and  noise, while the
de-energized electrode voltage represents only noise.  The
difference between the  two voltages is  measured yielding a
'clean" signal.  Because of this operating  scheme, the pulsed
dc mag meters are zeroed every cycle whereas AC meters require
stopping the flow for periodic re-zeroing.
          POWER
          SOURCE
          I20VAC
     PROCESS
     LIQUID
     FLOW
                                       METER OUTPUT SIGNAL

                                   CONVERTER/TRANSMITTER
                                             LINER MATERIAL
                                            FLOW TUBE
  ELECTRODE
MAGNETIC COILS
  Figure 2.1,  Magnetic flow meter construction.

-------
       TURBULENT
       VELOCITY
       FLOW
       PROFILE
                                                 MAGNET
                                                 COIL
      OUTPUT VOLTAGE = E0 = KBDV x 10 "4 VOLTS
                 WHERE K = COEFFICIENT TO ACCOUNT FOR NON-IDEALITY
                      B = MAGNETIC FLUX DENSITY, TELSA
                      D = PIPE DIA. (DISTANCE BETWEEN ELECTRODES), METERS
                      V = AREA - AVERAGE VELOCITY OF FLOW,  M/S
           Figure 2.2.  Magmeter  induced voltage.
C.   Accuracy and Repeatability

     The accuracy of a magnetic  flow meter should be within £1.0% of
     full scale and should not exceed £3.0% of  indicated  flow when
     operating in the lower one-third of the meter  range.

     The repeatability should be within £0.5% of full  scale.

     The above accuracies  reflect  the expected performance  under
     typical field conditions.   These meters are capable of
     improved performance  under  ideal conditions.

    These  requirements  can be met by  the  inherent  characteristics
    of  present-day  mag  meter design;  however,  several  circumstances
    will degrade  these  levels of operation,  including:

    1.   Plow conditions.

         Flow-disturbing piping obstructions located too near the
         meter  inlet  and outlet may add an  additional  1 -  10% of
         uncertainty  to  the measured  flow.   Avoid  locating the
         following  obstructions nearer  than five pipe  diameters  to
         the meter  inlet or outlet:

         a.    Valves,

         b.    Gates,

-------
           c.    Tees,

           d.    Elbows,

           e.    Pumps, and

           f.    Severe reducers and expanders (  30°  included angle).

           Refer to Part  E,  Installation,  for detail.

     2.    Meter orientation.

           Meter orientation leading to a  non-full meter  pipe (i.e.,
           trapped gases) or resulting in  material buildup on the
           electrodes severely degrades accuracy.  Refer  to Part E,
           Installation,  for detail.

D.   Manufacturer's Options

     1.    Electrodes.                                   .

           a.    Shape (see  Figure 2.3),
      WASHER
        NUTS'
        •INSULATING BUSHING

           FLUSH ELECTRODE
             (STANDARD)
                          vV-LINER
                                ELECTRODE

                                INSULATOR
                            —PIPE TUBE WALL-*
INSULATING WASHER
 LOADING SPRING
    TERMINAL
INSULATING BUSHING
                 BULLET-NOSED ELECTRODE
                      (PROTRUDING)
       Figure 2.3.  Mag  meter electrode  shape options.
                           45

-------
     b.    Materials:

          1)    316  Stainless  steel,

          2)    Platinum/iridium,

          3)    Tantalum,

          4)    Hastelloy,  and

          5)    Nickel.

     c.    Self-cleaning .

          1)    High frequency ultrasonic (continuous or
               portable).

          2)    Heat.

     d.    Field replaceable.

          1)    Available with self-sealing liners only, e.g.-,
               neoprene  or rubber (not available for
               Teflon-lined meters).

2.    Liner material.

     a.    The corrosive  and/or abrasive characteristics of the
          process liquid dictate proper selection of the liner
          material  and electrode construction (see Tables 2.1
          and 2.2).
                      i
3,    Mag/flow converter.

     a.    Auto zero calibration.

     b.    Output signal:  4-20 mAdc,  digital pulse, scaled
          digital pulse.

     c.    Face-mounted indicating meter.

4.    Grounding rings, straps, probes.

5.    Environment.

     a.    Corrosive resistant epoxy paint.

     b.    Protected from accidental or continuous submergence,
          NEMA 6 -  submersible, watertight.
                       46

-------
E.    Installation

     1.   Locate the meter on the discharge side of pumps and on the
          upstream side of throttling valves.

     2.   Locate the meter in a straight run of pipe free of valves
          or fittings with a  minimum of five diameters upstream and
          downstream length.

     3.   The  process conduit must  flow full of liquid.

     4.   Meter  sizing is  critical.   Size  the  meter  to provide  a
          fluid  velocity within the  following  ranges:

          a.   Non  solids-bearing liquids:   1-9  m/s  (3-30  ft/s).

          b.   Solids-bearing liquids:   1.0 - 7.5  m/s  (3.0 - 25.0 ft/s

          c.   Abrasive solids-bearing  liquids:   1.0 - 2.0 m/s
                                                 3.0 to  6.0 ft/s

          Appropriate reducers/expanders may be required  to achieve
          recommended operating velocities.

          Use the flow that will exist at startup for meter sizing.
          DO NOT USE 20 YEAR FLOW ESTIMATES FOR METER SIZING.

     5,   The meter must have self-cleaning electrodes, ultrasonic
          or heated, for all applications except where process water
          is equivalent to or better than secondary effluent quality.

     6.   Install the mag meter so it can be taken out of service
          for calibration and/or maintenance without disrupting the
          associated process.  Recommended isolation and bypass
          piping configurations are shown in Figure 2.4.
                          47

-------
       5 OIA. WIN.
          A
    MAG METER
       5 DIA. MIN.
                  NORMAL
                                      WITH CLEAN OUT TEE
 Figure 2.4.  Bypass  pipe  installation.
When the meter is to measure  process  liquids containing
solids, e.g., primary sludge, RAS,  WAS,  thickened sludge,
or when continuous electrode  cleaning is  not used, install
a cleanout tee as ""-own  in  Figure 2.4.

The decision to install  bypass  piping is  a value judgment
involving consideration  of  many factors  including:

a.   Pipe size,

b.   Available space, and

c.   The ability to shut down the line while maintaining
     process operation or shifting to a  parallel process
     unit.

                 48

-------
7.   Properly ground all mag meters using stainless steel
     grounding rings and grounding straps supplied by  the meter
     manufacturer.  The grounding rings should have an  inside
     diameter one cm (1/4 in) less than that of the meter (for
     meters 10 cm  4 in  in diameter or larger).  Place  them on
     both flanges with grounding straps as shown in Figure  2.5.
                   Pn  f
                 i "*'       ~i r-
                               GROUNDING  RING
                                     GROUNDING STRAPS
                                     GROUNDING STRAP
                                     TO EARTH GROUND
         Figure  2.5.   Mag meter  grounding.

     Always ensure that the plant electrical system ground near
     the meter location provides adequate grounding.  If a
     plant-wide grounding grid is available, ground the meter
     to it.

8.    Additional installation information.

     a.   Avoid locating mag meters near heavy induction
          equipment because it causes meter operational
          problems (100 HP motors and larger, no closer than 20
          feet).

     b.   Provide sufficient space to facilitate calibration,
          in-line maintenance, or meter removal.

     c.   Orient the meter  so the electrodes lie in a plane
          parallel to the floor.

     d.   Wall-mount the transmitter/converter within sight of
          the meter in a NEMA 4 enclosure (NEMA 6 if possible
          submergence), or  flush panel mounted so the cable
          length from the meter does not exceed 60m (200 ft).

-------
          e.    Use driven-shield signal  leads and route them between
               the transmitter and meter through dedicated 2 cm
               (3/4 in)  conduit.  Route  power wiring in separate
               conduit.

          f.    Torque  flange connections to the manufacturer's
               installation specifications.

          g.    Wire power  to the transmitter/converter and the coil
               driver  through the same dedicated circuit.   If
               separate  circuits are used for transmitter/converter
               power and coil driver power, both circuits  must
               originate from the same phase of the primary power
               feed.

          h.    Mount the meter in a vertical pipe run with the flow
               direction upward.  Install air bleed valves for
               meters mounted horizontally.

          i.    Metered lines should not self-drain when shut down.

          j.    Provide for flushing and filling with clean water in
               sludge applications where intermittent operation is
               expected.

P.    Designer Checklist

     Use the following checklist when designing or reviewing mag
     meter applications.  Verify affirmative all checklist items for
     proper application  and installation.

     1.   Does the process liquid to be measured have a measured
          conductivity greater than 5 micro-mhos per centimeter?

     2.   Will the pipe  flow full under ALL conditions, excluding
          shutdown?

     3.   If intermittent flow is expected, will the meter remain
          full at no flow?  Does the transmitter have low flow zero
          cut-out circuitry?

     4.   Does the meter size ensure a flow velocity between 1.5-7.5
          m/s (5-25 ft/s) for solids-bearing liquids or 1-9 m/s
          (3-30 ft/s), for non solids-bearing liquids?

     5.   Has the proper liner material been selected for the
          particular application?

     6,   DO the electrodes require and have continuous cleaning
          'capabilities?
                           50

-------
     7.   Are all piping elements/obstructions located at a minimum
          distance of five pipe diameters upstream or downstream of
          the meter?

     8.   Have grounding rings and straps been provided, and is the
          meter grounded to a true ground?

     9.   Have bypass piping and valving been provided?

     10.  Is signal wiring between the transmitter and meter as
          specified by the meter manufacturer and routed in separate
          conduit?

     11.  Has a dedicated power source been provided for the mag
          meter?

     12.  Has the proper electrode material been"selected to avoid
          excessive wear?

     13.  Is the selected liner material compatible with the
          expected operating temperature?

     14.  Does the design provide environmental temperatures within
          the range specified by the manufacturer for both the meter
          tube and the transmitter/converter?

G.   Acceptance and Performance Monitoring

     Include provisions for acceptance testing and performance
     monitoring as described in Section 7,2, relating to:

     a.   Hydraulic flow testing,

     b.   Electrical ground testing, and

     c.   Verification of manufacturer accuracy and factory
          calibration documentation.

H.   Maintenance and Calibration

          Task                    Frequency

     1.  Calibrate transmitter.   Once each month.

     2.  Plow calibrate           Every three months.
         the meter.

I.   Deficiencies

     The following problems are commonly encountered with existing
     mag meter installations.
                          51

-------
     1.    Velocity skewing created by piping obstructions located
          too near to the meter cause accuracy problems and liner
          wear.  In severe cases the obstructions cause the liner to
          be ripped away.

     2.    Meter sizing does not maintain adequate flow velocities.
          Often this results from over design for "future" flow
          rates.

     3.    Improper installation results in non-full pipe during low
          flows.

     4.    Solids coating the electrodes due to lack of automatic
          electrode cleaning cause low flow velocity and/or
          intermittent flow.

     5.    Meter and/or transmitter located so that calibration and
          maintenance accessibility are difficult.

     6.    Isolation and bypass piping is not installed, requiring
          shutting down the process for meter zeroing and meter
          removal (when required).

     7.    Infrequent calibration.

     8,    No provisions are made for meter calibration.

     9.    Improper grounding.

J.   References

     1.    Liptak, B.G., and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement.  Chilton Book Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.

     2.    Kulin, G.  Recommended Practice For The Use Of
          Electromagnetic Plow Meters In Wastewater Treatment
          Plants.  EPA 600/2-84-187 U.S. Environmental Protection
          Agency, Cincinnati, Ohio, November, 1984.

     3.    Fisher & Porter Company.  Instruction Bulletin No.
          10D1435A Warminster, Pennsylvania, 1969, Revision 1.

     4.    Sybron/Taylor Corp.  Magnetic Flow Meter - Basic Theory.
          Product Data, PDS-15E001 Issue 3.  Rochester, New York.

     5.    Sybron/Taylor Corp.  Magnetic Flow Meter - Application.
          Product Data, PDS-15E002 Issue 3,  Rochester, New York.

     6,    Sybron/Taylor Corp.  Magnetic Flow Meter - Installation.
          Product Data, PDS-15E003 Issue 2.  Rochester, New York.
                           52

-------
2.2  SONIC FLOW METERS

     A.    Applications
          Sonic flow meters are available in two basic types; the
          transmissive (through beam)  type and the reflective
          (frequency-shift) or Doppler type.

          1,    Transmissive type.

               Application of transmissive type (through-*beam) sonic
               flow meters are indicated where the following
               conditions exist:

               a.    Head losses must be minimized.

               b.    Process pipe flows full.

               c.    The amount of suspended solids and entrained air
                    bubbles in the process liquid together are
                    "equivalent" to no greater than 3% suspended
                    solids by weight.

               d.    Process liquid temperatures range between
                    00-800 c (320-180° F).

               e.    Line size is small enough so the sonic signal
                    attentuation does  not cause a problem.  Consult
                    meter manufacturer about applications in lines
                    larger than 100 cm (42 in.).
TABLE  2.3.  TRANSMISSIVE SONIC FLOW METER APPLICATION GUIDELINES
     Recommended                       Not Recommended

     Primary effluent                  Raw sewage
     Mixed liquor                      Primary sludge
     Secondary clarifier effluent      Thickened sludge
     Plant final effluent              Nitrification RAS
     Process (wash) water              Nitrification WAS
     Return activated sludge (RAS)
     Waste activated sludge (WAS)
                               53

-------
         2.   Reflective type.

             Conditions for suitable applications  of  reflective
             type  (Doppler) sonic flow  meters  are  as  follows:

             a.    Head loss must be minimized.

             b.    Process pipe flows full.

             c.    The amount of solids  ind  the entrained  air
                   bubbles in the process  liquid must  be equivalent
                   to a suspended solids concentration greater  than
                   2% but less than 4% by  weight.

             d.    Flow velocities at the  transducer must  be
                   maintained between 1-9  m/s (3-30 ft/s).

             e.    Pipe wall thickness mast  be  less than 5 cm  (2
                   in) thick.

             f.    The pipe is not constructed  of,  or  lined with,
                   an aggregate material.

             g.    The thickness of the  pipe wall  is exactly known.
TABLE 2.4.  REFLECTIVE SONIC FLOW METER APPLICATION GUIDELINES
   Recommended                        Not  Recommended

   Raw sewage                         Secondary clarifier effluent
   Primary  sludge                     Plant  final  effluent
   Thickened sludge                  Process (wash) water
         3.    Varying  stream conditions.

              A note of caution for the "recommended/not
              recommended"  process  applications:   Determine the
              range of conditions under wh-' ;h a sonic flow meter
              will  have to  operate;  fluctuating flow conditions
              may cause intermittent operation of the meter.
                              54

-------
B.   Principle  of  Operation

     1.   Transmissive sonic meters.

          The transmissive sonic  flow meter (also called
          through  beam or time-of-travel  meter) measures  fluid
          velocity by measuring the difference in the time
          required for a sonic pulse to  travel a specific
          distance through the fluid in  the same general
          direction as fluid flow, and the time required  for a
          sonic pulse to travel the same distance in the
          opposite direction.  This meter is available  in two
          types:  (1) a pipe section with integral well-mounted
          transducers and (2) a direct-mounted version  with the
          transducers mounted externally to an existing pipe.
          Both  types use the same operating principle;  Figure
          2.6 shows the pipe section type.
   NOTES'

     METER BODY RECOMMENDED
     TO BE MOUNTED IN
     VERTICAL PIPE.
     TRANSMITTER RECOMMENDED \ 1
     TO BE MOUNTED ON THE    ^
     METER BODY.
     WIRING:
     -FLEXIBLE CONDUIT TOR
       TRANSDUCER/TRANSMITTER
       WIRING.
     -RIGID CONDUIT (2) FOR
       POWER 8 SIGNAL.
                                           PROCESS PIPING

                                          METER FLANGE
AVERAGE FLUID VELOCITY = 2COS9
 AF= DOWNSTREAM FREQUENCY
    UPSTREAM FREQUENCY
  D = DISTANCE BETWEEN
    TRANSDUCERS
    TRANSDUCER HOUSING
   (TRANSMITTER/RECEIVER)
                              FLOW
            Figure 2.6.  Transmissive  sonic flow meter.
           Sonic transducers are energized alternately by
           electrical pulses and emit  sonic pulses across  the
           flow.   The pulse whose  directional component  is
           downstream traverses the  pipe in a shorter time  than
           the  pulse traveling against the flow (upstream).
           This time difference is proportional to the flow
           velocity, and an output signal linearly proportional
           to the flow rate is computed in the meter
           transmitter.
                            55

-------
     2.    Reflective (Dopplet)  sonic meters.

          Figure 2.7 illustrates that operation of the
          reflective,  or  Doppler,  sonic flow meter and is based
          on a principle  different from the transmissive type.
          The single transducer used is mounted on the external
          wall of the pipe.   A signal of known frequency is
          sent into the fluid where it is reflected back to the
          transducer by suspended  particulates and/or gas
          bubbles.   Because  the reflective matter is moving
          with the  process stream, the frequency of the sonic
          energy waves is shifted  as it is reflected.  The
          magnitude of the frequency shift is proportional to
          the particle (flow) velocity and is converted
          electronically  to  the meter output signal linear to
          flow.
                                          FREQUENCY CHANGE
                                          = FLUID VELOCITY
           Figure 2.7,  Reflective sonic flow meter.
C.   Accuracy and Repeatability

     The accuracy and repeatability of sonic flow meters vary
     between the two types; the transmissive type provides a
     more accurate flow rate signal than does the reflective
     type.  The following limits should be required when
     considering either type for any of the applications
     previously listed:
                           56

-------
     Transmissive:           accuracy, .+2% of actual flow
     (through beam)          repeatability, _+!% of actual
                             flow

     Reflective:             accuracy, _+5% of actual flow
     (Doppler type)          repeatability, jKL% of actual
                             flow

Purchase of sonic flow meters which meet these accuracy
limits does not assure that the limits will be met in
operation.  Several factors can degrade accuracy and must
be adequately addressed during the design phase.  These
factors are:

1.   Flow conditions.

     Flow-disturbing piping obstructions located too near
     the meter inlet may add up to 10% of error to the
     measured flow rate.  The following obstructions
     should not be located nearer than 7 to 10 pipe
     diameters from the meter inlet, or 5 pipe diameters
     from the outlet  (on flow-tube, transmissive meters)
     or within these distances from the external
     transducer of the Doppler type meter.

     a.   Valves  (modulating and isolating).

     b.   Gates.

     c.   Elbows and tee's.

     d.   Pumps.

     e.   Severe reducers and expanders (> 30 degrees
          included angle).

     Also, skewing of the velocity profile will result if
     the recommended straight lengths of pipe are not
     provided upstream and downstream of the meter.
     Skewing will cause errors in the flow measurement.

     Refer to Part E, Installation, for additional details.

2.   Meter orientation.

     Meter orientation leading to a non-full pipe or
     resulting in material buildup or deposition will
     severely degrade meter accuracy.  Refer to Part E,
     Installation, for detail.
                      57

-------
D.   Manufactured Options

     1.   Transmissive (through beam) - only.

          a.    Meter tube construction:

               1)   Stainless steel.

               2)   Carbon steel.

          b.    Meter tube end connections:

               1)   150 Ib ANSI RF flange.

               2)   300 Ib ANSI RF flange.

               3)   Victaulic.
                                 •
               4)   Plain.

          c.    Transducer mounting:

               1)   Wetted, with flush water port.

               2)   Wetted, with epoxy window (Teflon-optional)

               3)   Wetted, removable without process
                    disruption,

     2.   Reflective (Doppler) - only:

          a.    Transducer mounting:

               1)   External, clamp-on.

               2)   Wetted, with flow tube.

     3,   Common options:

          a.   Input power:

               1)   115 VAC,  50-60 Hz.

               2)   220 VAC,  50-60 Hz.

               3)   24 VDC.

          b.   Transmitter:
                           '58

-------
               1)   Outputs:

                    a)   4-20 mAdc.

                    b)   0-10 VDC.

                    c)   Pulse rate.

               2}   Integral flow rate indicator/totalizer.

               3)   Adjustable relay contact alarm outputs.

          c.   Environment:

               1)   Temperature:   -2QO to 60° c (-4° to
                                  1400 F).

E.   Installation

     1.   Install transmissive sonic flow meters having wetted
          transducers so the meters can be taken out of service
          for calibration and/or maintenance without disrupting
          the associated process.  Recommended bypass
          configurations are the same as those recommended for
          magnetic flow meters and are shown in Figure 2.4.

          The decision to -install bypass piping involves such
          considerations as pipe.size, available space, and the
        i  ability to shut down the line while maintaining
          process operation or shifting to a parallel process
          unit.

     2.   Locate meters on the discharge side of pumps and on
          the upstream side of throttling valves if these
          devices are near the required meter location.

     3.   Flow velocities through the meter should be
          maintained between 1-9 m/s (3-30 ft/s).

          Appropriate reducers/expanders may be required to
          achieve recommended operating velocities.

          Use the flow that will exist at start-up for meter
          Sizing.  DO NOT USE 20 YEAR FLOW ESTIMATES FOR METER
          SIZING.

     4.   Provide straight runs of pipe upstream and downstream
          of the meter as described in Part C,  Accuracy and
          Repeatability.
                           59

-------
     5.    Orient spool-piece type meters in, or locate clamp-on
          type meters on/ vertical process piping where
          possible,  with flow direction upward only.  Install
          air  bleed  valves when horizontally mounted.

     6,    Metered lines should not self-drain when shut down.

     7.    Locate the meter in an accessible location with
          sufficient space for calibration, in-line
          maintenance, or meter removal.  Install the
          ttansmitter as close as possible (3.7 m, 12 ft) to
          the  clamp-on transducer.  When a meter tube is used,
          mount the  transmitter directly on the tube.

     8,    Install clamp-on transducers according to the
          manufacturer's suggested procedures.  Be sure that no
          air  babbles are present in the epoxy sealant compound.

     9.    Use  separate conduit to wire line power and signal
          wiring.

     10.   Follow precisely the manufacturer's guidelines for
          aligning sonic transducers to the pipe.

     11.   Install the transmissive meter as a spool piece for
          pipes ranging in size from 91 - 7.6 cm (36 - 3 in).
          For  pipes  smaller than this, mount the transducers in
          an axial configuration as shown in Figure 2.8.
                                            METER
                                            FLANGE
                                              PROCESS
                                               PIPE
                                              /
                                                   FLOW
jUDO 	 CnDC

Y1
\
CONDUIT
CONNECTION


I—I 1


a
5

\
TRANSDUCER
HOUSING
                   NOTE:
                    L METER TUBE SHALL ALWAYS BE
                      MOUNTED IN HORIZONTAL PROCESS PIPE.
Figure 2.8.  Transmissive sonic meter, axial configuration.
                           60

-------
F.    Designer Checklist

     Use the following checklist when designing or reviewing
     sonic flow meter applications.   All checklist items should
     be answered yes for proper application and installation.

     1.   Common items.

          a.   Will the pipe flow full under all conditions?

          b.   If intermittent flow  is expected, will the pipe
               remain full  at no-flow conditions?

          c.   Are all piping elements/obstructions located a
               minimum distance of 7-10 pipe diameters upstream
               and 5 diameters downstream?

          d.   Are the meter and transmitter easily accessible?

          e.   Will adequate flow velocities be realized, 1-9
               m/s (3 - 30  ft/s)7

          f.   Is the meter located  correctly in relation to
               pumps and throttling  valves?

          g.   Does the design provide environmental
               temperatures within the manufacturer's specified
             '  range?

          h.   Has a sample of the process fluid been tested
               for sonic transmittance?

     2.   Transmissive (through beam) items.

        .  a.   Have the proper spool piece material and end
               connections  been provided for?

          b.   Is the transmitter mounted on the spool piece?

          c.   Is the process liquid recommended in Table 2.3?
               Is the amount of air  bubbles and solids less
               than 3% by volume?

          d.   Is the process liquid temperature between
               00-80° C (30-180° F)?
                           61

-------
     3.   Reflective (Doppler) items.

          a.   Is the process liquid recommended in Table 2.4?
               Does it have a solids and/or air bubble content
               greater than 2% but less than 4%?

          b.   Is the clamp-on transducer located where no
               excessive pipe and/or liquid-transmitted
               vibration will occur?

          c.   Is the pipe inside diameter and wall thickness
               known accurately?

H.   Acceptance and Performance Monitoring

     Provide for acceptance testing and performance monitoring
     as described in Section 7.1, relating to:

     1.   Hydraulic flow testing.

     2.   Verification of manufacturer accuracy and factory
          calibration documentation  (reflective type meters are
          rarely factory calibrated).

I.   Maintenance and Calibration

     The recommended calibration interval for sonic flow meters
     is every two months.

J.   Deficiencies

     The following problems are commonly encountered with
     existing sonic flow meter installations:

     1.   Piping obstructions located too near to meter causing
          accuracy problems.

     2.   Meter sizing is such that adequate flow velocities
          are not maintained.  Many  times this results from
          over design for "future" flow rates,

     3.   Installation resulting in non-full pipe during low
          flows.

     4.   Solids coating due to low  flow velocity and/or
          intermittent flow.

     5.   Meter and/or transmitter located so that calibration
          and maintenance accessibility is difficult.
                          62

-------
     6.   Infrequent calibration.

     7.   No provisions for flow rate testing/calibration.

     8.   Solids concentration and/or entrained air greater
          than acceptable for transmissive type, resulting in
          poor accuracy or an unacceptable signal.

     9.   Solids concentration and/or entrained air less than
          required for reflective type, resulting in poor
          accuracy or an unacceptable signal.

     10.  Grease and scum buildup on pipe walls and wetted
          transducers,

K.   References

     1.   Liptak, B, G., and K.  Venczel.  Instrument Engineers
          Handbook of Process Measurement, Chilton Book
          Company, Radnor, Pennsylvania, 1969, Revised, 1982.

     2.   Brown, A. E.  Application of Flowmeters to Water
          Management Systems,  Presented to Instrument Society
          of America, ISA/81 Conference, Anaheim, CA, (October,
          1981).

     3.   Powell, D. J.  Ultrasonic Flowmeters, Basic Design,
          Operation and Criteria Application.  Plant
          Engineering, May, 1979.

     4.   Hall, J.  Choosing a Flow Monitoring Device.
          Instruments and Control Systems, June, 1981.
                          6-3

-------
2.3  TURBINE FLOW METERS

     A.    Application
          The following general conditions provide suitable
          applications for turbine flow meters:

          1,   The typical head loss through a turbine meter of
               21-35 kPa (3-5 psi) can be tolerated.

          2.   The process piping is full under flowing conditions.

          3.   The process liquid is relatively 'clear," i.e., a
               solids concentration less than 0.1% by weight (1000
               mg/1) and is free of fiberous materials and/or debris.

          4.   A maximum meter rangeability of 10:1 is acceptable.

          5,   An intermittent flow may be expected.
       TABLE  2.5.   TURBINE PLOW METER  APPLICATION  GUIDELINES
     Recommended                       Not Recommended

     Plant final effluent              Raw sewage
     Secondary clarifier effluent      Primary sludge
     Process (wash) water              Secondary sludge (RAS & WAS)
     Steam condensate                  Mixed liquor
                                       Primary effluent
                                       Chemical slurries
     B.   Meter Sizing

          Due to the nature of their linear-to-flow relationship,
          turbine meters must be properly sized by volumetric  flow
          rate.  A meter sized to a specified range of linear  flow  rate
          measurement should not be used for flow rates outside  that
          range.
                                 )

          Follow these guidelines when sizing a turbine meter:

          1.   The flow meter should be sized for 120-130% of  the
               maximum expected process flow rate.
                               64

-------
      2.    If  the meter  is sized by volumetric  flow  rate  (guideline
           No. 1), it will have a diameter smaller than the  process
           pipe.  See Figure  2.10 for  reducer/straight pipe
           installation.

      3,    If  the meter  size  is the same diameter as the  process
           pipe, its range will be severely  reduced  (to 2:1  or
           3:1); however, the head loss through the meter will be
           less than if  volumetrically sized.

      4.    Liquid cavitation  may occur in the meter  if upstream
           line pressure is not sufficient.  To ensure sufficient
           pressure, the downstream line pressure must be a  minimum
           of  2 times the meter head loss plus  1..25  times the
           liquid vapor  pressure.  If  this condition cannot  be met,
           a larger size meter with a  correspondingly reduced meter
           range is required.

      5,    Available turbine  meter sizes range  from  0.5-60.0 cm
           (3/16-24 in.) in diameter.

C.    Principle of Operation

      Turbine  flow meters consist of a pipe  section with a
      multi-bladed impeller suspended  in the fluid stream on a free
      running  bearing (see Figure 2.9).  The direction of rotation
      of the impeller is perpendicular to the flow direction, and
      the impeller blades sweep out nearly the full bore of  the
      pipe.  The impeller is  driven by the process liquid impinging
      on the blades.  Within  the linear flow range of the meter,
      the impeller's angular  velocity  is directly proportional to
      the liquid velocity which is, in turn, proportional to the
      volumetric flow rate.  The speed of rotation is monitored by
      an electromagnetic pickup coil which operates either on a
      reluctance or inductance principle to  produce a pulse.  The
      output signal is a continuous voltage  pulse train with each
      pulse representing a discrete volume of liquid.  Associated
      electronics units then convert and .display volumetric flow
      (flow rate) and/or total accumulated flow.

D.   Accuracy and Repeatability

     The accuracy and repeatability characteristics of turbine
     flow meters,  when properly applied and installed,  should be:

          Accuracy:                +0.25% of actual flow,  within
                                  the linear range of the meter.

          Repeatability:         ^0.05% of actual flow,  within
                                  the linear range of the meter.

-------
                         PICKUP COIL
                    ROTOR
                     UNIT
           UPSTREAM ASSEMBLY
          HANGER UNIT
                                            HOUSING
                                               DOWNSTREAM
                                                 HANGER
                                                  UNIT
                                     SPINDLE
             Figure 2.9.  Turbine  flow meter.
     Each turbine flow meter has a unique  "K"  factor  (the number
     of pulses per unit volume) which  is determined during factory
     calibration.  This factor is adversely  affected  by two
     conditions:

     1.   The liquid viscosity is significantly greater than that
          of clean water.  This condition  should not  occur in
          wastewater treatment facility applications  recommended
          in Table 2.5.

     2.   The moving components become impaired by buildup of
          solids and/or fiberous materials.

E.   Manufactured Options

     Turbine flow meter options available  to the buyer  are limited
     due to meter design standardization.  Typically, options are
     limited to wetted parts materials for additional protection
     against corrosion and some additional equipment  listed below:

     1.   Wetted parts materials:

          a.   Stainless Jteel (standard).

          b.   Hastelloy "C".

          c.   P.T.F.E. (bearings).
                          66

-------
     2.   Plow straightening vanes/elements.

     3.   An additional electromagnetic pickup and associated
          electronics for increased accuracy.

     4.   Turbine meters may require additional equipment for
          secondary readout and/or transmitter devices.   These
          should be purchased from the meter manufacturer.  If
          another supplier is used, take care to ensure that both
          units are compatible with regard to pulse shape,
          amplitude, width, and signal frequency.

     5.   Typical secondary elements may include:

          a.   Electromechanical rate indicator and totalizer,

          b.   Pulse-to-current transducer.

          c.   Signal pulse "preamplifier (for long distance pulse
               signal transmission).

F.   Installation

     1.   Flow-disturbing piping obstructions severely affect
          turbine meter accuracy.   Figure 2,10 shows the
          recommended installation piping and details, including a
          flow-straightening element.

     2.   When a flow-straightening element is used, the flow-
          disturbing effects of the following obstructions will be
          adequately damped in a minimum upstream  distance of 10
          pipe diameters (including the straightener).  NOTE:  If
          no flow-straightening element is used, extend  this
          minimum distance to 25 to 30 pipe diameters.

          a.   Valves.

          b.   Gates.

          c.   Tees.

          d.   Elbows.

          e.   Severe reducers and expanders (   30 degrees
               included angle).

     3.    Locate piping obstructions no nearer than 5  pipe
          diameters downstream from the meter.

     4.    Install  the meter  in a horizontal pipe run.
                         67

-------
     5.   Install the meter  on  the discharge side of pumps and  on
          the upstream side  of  throttling valves.

     6.   Shield the cable between the  turbine meter and
          electronics; minimize its  length,  and do not route it
          through areas of high electrical noise.
          CONCENTRIC
            CONE
                                 NOMINAL SIZE
                                  0 INCHES
                                                     CONCENTRIC
                                                       CONE
               ALTERNATIVE FLOW
              STRAIGHTENING VANES
                                   METER 8 STRAIGHTENER
                                      CONNECTIONS
              Figure  2,10.   Turbine meter mounting.
G.   Designer Checklist

     Use the following checklist when designing or reviewing
     turbine flow meter  applications.  All checklist items  should
     be verified affirmative for proper application and
     installation.

     1.   Is the intended  process liquid as recommended  in  Table
          2.5?

     2.   Can the expected head loss be tolerated from a hydraulic
          standpoint?

     3.   Is the expected  upstream line pressure great enough to
          prevent cavitation in the meter?

     4.   If the meter diameter is equal to the process  pipe, is
          an instrument  rangeability of 3:1 acceptable?
                           68

-------
     5.    Are all  pipe  obstructions  located at least a distance of
          5 pipe diameters  downstream and a minimum upstream
          distance of:

          a.    10  pipe  diameters (when a flow straightener is
               utilized)?

          b.    25-30 pipe diameters  (when a flow straightener is
               not utilized)?

     6.    Will the turbine  meter be  full under flowing conditions?

     7.    Is the process liquid essentially free of solids,
          fiberous materials, and/or debris?

     8.    Has the proper secondary flow indication device(s) been
          provided; has line power been provided, if required, for
          the device(s)?

     9.    Is the meter  easily accessible for maintenance?

     10.  Have provisions been made  for calibrating the meter?

H.   Acceptance and Performance Monitoring

     Provide for acceptance testing  and performance monitoring as
     described in Section 7.1, relating to:

     1.    Hydraulic flow testing.                    •

     2,    Verification  of manufacturer accuracy and factory
          calibration documentation.

     The meter constant "K", in clean water, is determined by the
     manufacturer prior to meter shipment.  If the  intended
     application process liquid has  physical characteristics that
     significantly differ from clean water, consult the
     manufacturer for additional testing data.

I.   Maintenance and Calibration

     Turbine meters normally do not require periodic calibration.
     When meter accuracy becomes questionable  (as observed through
     performance monitoring), examine it to determine maintenance
     requirements, or if none are required, determine a new  "K"
     factor by hydraulic testing.
                          69

-------
J,   Deficiencies

     The following problems are commonly encountered with existing
     turbine meter applications:

     1.   Inadequate upstream and downstream straight run piping,
          resulting in poor meter accuracy.

     2.   No flow straightening vanes, resulting in poor accuracy.

     3,   Meter sized too large, resulting in non-full pipe and/or
          poor accuracy at low flows.

     4.   Meter sized correctly, but reducers located too near
          inlet and outlet.

     5.   Meter applied to a process liquid with an excessive
          solids concentration.

K.'  References

     1.   Liptak, B. G., and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement, Chilton Book Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.

     2.   Foxboro Company.  Technical Bulletin No. TI, 16-6a.
          Foxboro, Massachusetts, January, 1971.
                          70

-------
2.4  VENTURI TUBES AND PLOW TUBES
     A.    Applications

          Recommended applications for venturi and proprietary flow
          tubes as primary elements include nearly all wastewater
          treatment process streams.   The most critical aspect of
          proper application is the type of pressure sensing system
          used to measure the differential pressure produced by the
          primary tube.

          Therefore, the recommended  applications for these
          instruments are listed by type of pressure sensing
          system.  The major types of sensing systems (described in
          Part C) are:

          1.   Opefi connection, without flushing (including
               piezometric rings).

          2.   Open connection, with flushing (excluding piezometric
               rings),

          3.   Diaphragm sealed connections.
         TABLE 2.6.  VENTURI AND FLOW TUBE APPLICATION GUIDELINES

                               Recommended
         Recommended         With Flushing or
       Without Flushing      Diaphragm Seals       Not Recommended

     Secondary effluent    Raw sewage            Primary sludge
     Final effluent        Primary effluent      Thickened sludge
     Process  (wash) water  Return activated      Chemical (corrosive)
                            sludge                slurries
                           Waste activated
                            sludge
                           Mixed liquor

          4,   Additional requirements for venturi and flow tube
               applications are:

               a.   The metering tube must flow full.

               b.   A maximum to minimum measuring range of 4:1 is
                    acceptable.

               c.   The Reynolds number of the process flow at the
                    meter should be greater than 150,000.
                               71

-------
          Do not use venturi  or  flow tube meters in line with a
          positive displacement  pump.   The resultant flow
          pulsations will produce  excessive signal noise and
          measurement  inaccuracy.

B.   Principle of Operation

     1.   Venturi tube.

          A venturi tube operates  on the  principle that a fluid
          flowing through a pipe section  that contains a
          constriction of known  geometry  will cause a pressure
          drop at the constriction area.   The difference in
          pressure between the inlet and  the constriction area
          (throat) is proportional to  the square of the flow
          rate.  Figure 2.11  shows a cut-away of a typical
          venturi tube.
                       -HIGH PRESSURE TAP

                                  -LOW PRESSURE TAP
          INLET
             INLET CONE
OUTLET CONE
          Figure 2.11.  Classic  venturi  tube.
     2.   General equation.
                 W » 353Yd2 VhP/(l-B2)

          Where:

          d » throat diameter  of  pipe.
          D » pipe inside diameter.
          h m differential produced  (in inches of water)
          Y m net expansion factor.
          S » d/D  (Beta ratio).
          P » specific weight.
          W » flow rate (pounds/hr).
                         72

-------
 Flow tube.

 Several manufacturers provide differential-causing
 flow tubes which are modified versions of  the
 classical venturi tube.  These devices operate  on  the
 same principle as the classical venturi; however,
 they provide features which make them more attractive
 for some applications, e.g., less space  is required
 for installation, less overall head loss,  and  lower
 installed cost.  Figure 2.12 shows three commonly
 used flow tubes.

 Both the venturi tube and the proprietary  flow  tubes
 are primary sensing elements and require a secondary
 element to measure pressure differential.
       LO-LOSS FLOW TUBE
                                     GENTILE OR BETHLEHEM
                                          FLOW TUBE
          CALL TUBE
Figure 2.12.  Proprietary flow tubes.

                 73

-------
C.    Pressure Sensing Systems

     The differential pressure created by a venturi or flow
     tube is generally measured by connecting a differential
     pressure (Ap)  transmitter to the sensing taps with pipe or
     tubing (tap lines).   The discussion here focuses on three
     common Ap transmitter connection methods.   Further
     information regarding the Ap transmitter and tap line runs
     is presented in Section 6.2 of this handbook.

     1.   Open connection.

          For this  method, the venturi tube pressure taps are
          connected directly to the Ap transmitter and the tap
          lines are allowed to fill with process liquid.  To
          avoid tap line  clogging, do not use this method for
          liquids with greater than 30 mg/1 solids.

          Providing a flushing water system for this sensing
          method allows the measurement of process liquids
          containing solids which would normally clog the
          sensing lines.   There are two methods of operating
          flushing  water  systems.   In one, flushing water is
          applied intermittently to purge solids from the tap
          line (measurement' is interrupted during the purge
          cycle).  In the second,  a continuous  equal flow of
          purge water is  applied to both taps to act as a
          barrier to solids.  As the purge water back pressure
          is measured in  the latter method, it  is critical that
          purge flows are equal.  Direct and flushing water
          connections are illustrated in Figure 2.13.

     2.   Piezometric rings.

          Piezometric rings may be used to sense inlet and
          throat pressures.  These are normally used in very
          large diameter  tubes where an average pressure is
          required  to compensate for velocity profile
          variations.  The rings consist of several holes for
          each tap  (in a  plane perpendicular to flow) connected
          to an annular ring.  They should be used or.j.y on
          clean liquids.   Flushing water systems cannot be used
          because the purge water short circuits within the
          annular ring to the nearest tap hole.

     3.   Diaphragm sealed sensors.

          The diaphragm sealed sensor method allows
          solids-bearing  liquids to be measured without a tap
          flushing system.  The process liquid is separated
          from the  tap lines and transmitter by a diaphragm.

                          74

-------
                          TO TRANSMITTER
                           HGH PRESSURE
                             FLUSHING
PURGE
                               TO TRANSMITTER
                          WITH CONTINUOUS FLUSHING
         Figure 2.13.   Typical  differential piping.
                             75

-------
D.   Accuracy and Repeatability

     The accuracy and repeatability of venturi and proprietary
     flow meters vary.  The characteristics of the secondary
     element (transmitter) must also be included in the total
     accuracy figure.  The following limits are generally
     attainable for the  previously listed applications:

     1.   Classical      Accuracy, _+!% of actual flow.
          venturi and    Repeatability, _+!%.
          Ap transmitter

     2.   Proprietary    Accuracy, _+!% - 3% of actual flow.
          flow tubes     Repeatability, _+!%.
          and Ap
          transmitter

     These levels of accuracy reflect optimum values achievable
     for proper application and installation.  Factors which'
     degrade these levels include improper tube sizing (Beta
     ratio to high or low for the expected flow range), and
     piping elements which disrupt the velocity profile.

E.   Manufactured Options

     1.   Primary meter tube:

          a.   Single sensing ports.

          b.   Piezometer ring sensing.

          c.   Inspection openings.

          d.   Manual rodders for cleanout of the sensing ports.

     2.   Sensing system:

          a.   Conventional, or

          b.   Diaphragm sealed.

     3.   Secondary element (transmitter):

          a.   Differential pressure transmitter  (see Section
               6.2).

          b.   Manometer transmitter (not recommended).
                          76

-------
F.   Installation

     1.   Primary system.
          a.   Venturi and flow tubes may De  installed  in any
               position to suit the  requirements  of  the
               application and piping as long as  the meter
               flows full.

          b.   For best accuracy, flow disturbing obstructions
               (fittings) should not be located too  near  the
               meter inlet.  The following guidelines indicate
               the minimum upstream  distance  of straight  pipe
               recommended between the fitting "and the  meter
               inlet:

               1)   Reducers      8  diameters of  reduced  pipe
                                  size.

               2)   Expanders      4 diameters.

               3)   Fully open     5 diameters.
                    valve

               4)   Check valve   12 diameters.

               5)   Throttled     20 diameters.
                    gate or ball
                    valve

               6)   900 bend(s)   4  diameters.

               For more information  on lengths of straight pipe
               runs, see References  8, 9 and  10.

          c.   If a flow control valve is required in the line,
               it should be placed a minimum  of 5 pipe
               diameters downstream  of the meter  tube.  As seen
               in 5) above, to place the valve upstream
               requires a much greater straight run  of  pipe.

          d.   Locate all downstream pipe fittings a minimum
               distance of 4 pipe diameters downstream  of the
               throat tap(s).

          e.   Place the meter tube  a minimum distance  of 10
               diameters downstream  from the  pump discharge.
               The meter tube can be located  on the  suction
               side of a centrifugal pump only if
               subatraospheric pressure can be avoided.
                        77

-------
     f.    Install  the primary and secondary flow elements
          in an accessible location with suitable space
          for maintenance and calibration.

     g.    Orient single  tap meters (at inlet and throat)
          in the process piping so that the taps lie in
          the upper  half of the meridian plane.

2.    Secondary system.

     a.    Place the  differential pressure transmitter
          below the  hydraulic grade line to facilitate
          positive gas bleeding.

     b.    Place an indicator gauge (A p) near the primary
          element for convenience in calibration and
          performance checking.

     The following refer to all installations except those
     having diaphragm-sealed sensors (see Figure 2.13).

     c.    If there is a  possibility of the tap lines
          freezing,  use  insulation and heat tape to wrap
          them.

     d.    Install tap line (connecting) tubing so that it
          has a minimum  downward slope from the meter of 1
          in 12.

     e.    Install a  bleed valve or gas collector at the
          highest point  in the tap line run,

     f.    Provide valves to isolate the transmitter for
          calibration,

     g.    Provide a  flushing water system if the process
          liquid contains greater than 30 mg/1 of solids.

     h.    Use connecting tubing no smaller than 1 cm  (3/8
          in) in diameter.

     The following refer to installations where continuous
     flushing is required  (see Figure 2.13).

     i.    The head loss in the tubing between the flushing
          water connection and the sensor tap should be
          the same in both lines so the pressure
          differential is  unaffected.

-------
          j.   The flushing water supply pressure should be at
               least 70 Kpa (10 psi) higher than process
               pressure.

          k.   Equip the flushing water supply line for each
               tap with a rotameter for visual inspection and
               adjustment of purge flow.

G.   Designer's Checklist

     Use the following checklist when designing or reviewing
     venturi and proprietary flow tube applications.   All
     checklist items should be answered yes for proper
     application and installation.

     1.   Is the process liquid recommended in Table 2.6
          compatible with the type of meter under consideration?

     2.   Will the meter tube flow full?

     3.   Is a maximum to minimum measurement range of 4:1
          acceptable?

     4.   Is the Reynolds number at the meter expected to be
          150,000 or greater?

     5.   Has the meter tube been sized to accommodate the
          present flow range .(bear in mind that meters sized
          for a 20 year projected flow are typically oversized)?

     6,   If the meter is to measure a solids-bearing liquid:

          a.   Are single sensor taps being used as opposed to
               a piezometric ring?

          b.   Has either a flushing system or diaphragm-sealed
               sensor system been provided?

     7.   Is adequate straight run piping provided up and
          downstream from the meter tube (see Part F,
          Installation)?

     8,   Have provisions been made for bleeding and flushing
          tap lines?

     9.   Are the tap lines sloped properly?

     10.  Are both the meter and secondary elements readily
          accessible?

-------
     11.  Will the meter be placed in a process line having
          smooth dynamics, e.g., not pulsating as in positivfe
          displacement pump applications?

H.   Acceptance and Performance Monitoring

     Provide for acceptance testing and performance monitoring
     as described in Section 7.1, relating to:

     1.   Hydraulic flow te>r _ing.

     2.   Verification of manufacturer accuracy and factory
          calibration documentation.

I.   Maintenance and Calibration

     1.   Primary system.

          a.   If the tube has manual rodders (bayonets), use
               these weekly or when the flushing water (if
               used) flow rate decreases.

          b.   If annular rings are included with the tube,
               bleed off gas periodically.

          c.   If performance monitoring indicates an accuracy
               change, test the primary with a portable
               manometer.

     2.   Secondary systems.

          a.   Bleed tap lines of entrapped air regularly.

          b.   Re-calibrate the transmitter monthly using a
               portable manometer.

J.   Deficiencies

     The following problems are commonly encountered with
     existing venturi and flow tube applications:

     1.   Meter oversized, low flow measurements are lost due
          to square root function cut-off.

     2.   Met-.ers installed in process lines having pulsating
          flow (reciprocating pumps), causing erroneously high
          flow rates.

     3.   Tap lines inadequately sloped and/or not provided
          with bleed valves, causing gas buildup.
                          80

-------
     4.    Improper differential range selection for  the ^p
          transmitter.

     5.    Inadequately designed flushing systems which skew the
          pressure differential.

     6.    Insufficient straight run piping upstream  and
          downstream of the meter.

K.   References

     1.    Liptak, B. G., and K. Venzcel.  Instrument Engineers
          Handbook of process Measurement.  Chilton  Book
          Company, Radnor, Pennsylvania, 1969,  Revised, 1982.

     2.    Spink, K. L.   Principles  and Practice of Flow Meter
          Engineering,  9th edition.  The Foxboro Co., 1967.
                                                        •
     3.    Water pollution Control Federation.  Instrumentation
          in Wastewater Treatment plants.  WPCF Manual of
          Practice No.  21, 1978.

     4.    International Standards Organization.  Measurement of
          Fluid Flow by Means of Orifice Plates, Nozzles and
          Venturi Tubes Inserted in Circular Cross-Section
          Conduits Running Full. ISO/DIS 5167, 1976, draft
          revision of R781.

     5.    International Standards Organization.  Fluid Flow in
          Closed Conduits—Connections for pressure  Signal
          Transmissions Between Primary and Secondary
          Elements.  ISO 2186 - 1973.

     6.    American society for Testing and Materials.  Standard
          Method of Flow Measurement of Water by the Venturi
          Meter Tube.  ASTM D2458-69.

     7.    Benson, J. E.  Process Instrumentation Manifolds.
          Instrument Society of America, Research Triangle
          Park, NC, 1981.

     8.    Fluid Meters, Their Theory and Application.  Report
          ASME Research Committee on Fluid Meters, American
          Society of Mechanical Engineers, New York, New York,
          1971, 6th Edition.
                        81

-------
9. _  Sprenkle, R.  E.   Piping Arrangements for  Acceptable
     Flowmeter Accuracy.   ASME Transactions 67:345,  New
     York, New York,  1945.

10.  Starret, P. S.,  P. F. Halfpenny and H. B. Noltage.
     Survey of Information Concerning the Effects of
     Nonstandard Approach Conditions Upon Orifice and
     Venturi Meters.   Paper presented at Winter Annual
     Meeting, American Society of Mechanical Engineers,
     New York, New York,  1965.
                   82

-------
3.0  FLOW MEASUREMENT,  CLOSED CONDUIT GAS FLOW


     3.1  ORIFICE PLATE
      •
          A.    Application

               The following general conditions provide suitable
               applications for orifice plate gas flow meters:

               1.   Clean gas, or steam.

               2.   A relatively large head loss is acceptable.

               3.   The Reynolds number at minimum flow is greater  than
                    10,000.

               4.   A meter maximum to minimum ratio of 3:1 is acceptable.
             TABLE  3.1.   FLOW MEASUREMENT,  CLOSED CONDUIT GAS FLOW
                                 APPLICATION GUIDELINES

                    Recommended               	Not  Recommended
          Boiler steam                       Wet steam
          Compressed digester gas            Low pressure  (uncompressed)
          Natural gas                          digester gas
          Activated sludge treatment         Strongly corrosive gases
            - blower air
            - oxygen
          Incinerator draft/blower air
          Aerated grit chamber, air flow

          The discussions, in this section pertain to concentric orifice
          plates.  Other configurations, segmental and eccentric,  are
          available to accommodate particular application  problems.

          B.   Sizing Guidelines

               Proper sizing of the orifice plate is required  for  accurate
               flow measurement.  Use the following guidelines:
               1.
                    Plate  Thickness

                    a.   Pipe I.D. from  5-20 cm  (2-12  in):   0.3  cm (1/8 in)
                         thick.
                                               i
                         Pipe I.D. 35 cm (14 in) and larger:   0.6 cm (1/4
                         in) thick.  	   ~
                                    83

-------
          b.   Bevel plates  thicker than 0.3 cm  (1/8  in) on  the
               downstream  orifice edge as shown  in Figure  3.1.
                                         BEVEL WHERE
                                         THICKNESS IS
                                         GREATER THAN
                                         3mm (1/8 IN)
                                         OR THE ORIFICE
                                         DIAMETER IS LESS
                                         THAN 25mm  (UN)
                  PIPE
                 INTERNAL
                 DIAMETER
3mm (I/8IN)
MAXIMUM
- 3-l3mm
 (1/8-1/2 IN)
          Figure  3.1.  Concentric orifice plate.
     2.   Orifice diameter.

          The Beta  ratio  is  defined as the ratio of orifice
          diameter  (d)  to the pipe I.D. (D) and is critical  for
          accurate  flow measurement.  For air and steam  flow
          measurement,  it is recommended that the Beta ratio be
          greater than  0.2 but less than 0.7(5).  The flow
          calculations  used  for determining the Beta ratios  are
          standardized  but rather complex.  These calculation
          methods are thoroughly covered in References 2 and 7.

C.   Principle of Operation

     Orifice plates are differential-producing head-type flow
     measuring devices  made  of a thin, flat plate having an
     opening  (orifice).  When installed in cross section with the
     process pipe,  orifice plates cause .an increase in the flow
     velocity as  the process gas moves through the orifice,
     causing a corresponding decrease in downstream pressure.  A
     differential pressure measuring device is connected across
     the orifice plate  to sense the differential pressure.  Figure
     3.2 illustrates this principle.

-------
    104-
                 DIFFERENTIAL
               |   PRESSURE   I
               L_MEASUREMENTj
         Figure 3.2.  Pressure profile.
The orifice plate flow meter is a primary  sensing  element
which creates a pressure differential  proportional to the
square of the flow rate.  This pressure  is measured by a
differential pressure sensor  (Ap) which  converts the
differential pressure to either a voltage  or  a current
signal.  A secondary element to convert  the non-linear
differential pressure into a linear  flow rate is required.
This can be done using a square root scale, square coot
extractor or computer.

Location of the pressure taps determines the  exact
relationship between differential pressure and flow rate.
These relationships are stated  in standard reference material
(2, 7).  The basic equations are:
For gas flow:  Q =
                           (eq.l)
For steam flow:  W  = K
Q
K
                              (eq.2)
    volume flow  rate  (scfh)
    basic orifice expansion,  flow and conversion factors
    that usually are constant for a  given application
h * differential pressure  across  the orifice in inches of
    water
P = absolute flowing pressure,  psia
T * absolute flowing temperature  (OR a OF + 460)
G 3 specific gravity of  gas  (air  » 1.0)
W = mass flow  in pounds  per hour  (Ib /hr)
V  » specific  volume  (ft3 AD  )  determined from Standard
     Steam Tables
                         85

-------
D.   Accuracy and Repeatability

     The total accuracy and repeatability of an orifice plate
     flow-measuring system must include tha accuracy and
     repeatability of the orifice,Ap sensor, and the square root
     extractor.  The following limits are achievable by orifice
     plate meters for the applications listed in Table 3.1:

     1.   Accuracy:          +1/2  to ±2% of full scale.

     2.   Repeatability:     +1.0% of full scale.

     These accuracy levels reflect c^cimum values achievable by
     the measuring system when properly applied and installed.
     The main factors which will degrade these levels include:
    .improper orifice sizing with  respect to the Beta ratio; flows
     either less or greater than anticipated, and" piping
     configurations which disrupt  the velocity profile.

E.   Manufactured Options

     1.   Type of construction materials.

     2.   Pressure connection location.

          a.   Flange taps (standard).

          b.   Vena contracta taps.

          c.   Radius taps.

          d.   Corner taps.

     3.   Orifice shape and location:

          a.   Concentric  (standard), with or without drain and
               vent holes.

          b.   Eccentric, with or  without drain and vent holes.

          c.   Segmental, with or  without drain and vent holes.

     4.   Removable orifice plate  (without process disruption).

     5.   Secondary element:

          a.   Differential pressure transmitter  (standard).

          b.   Manometer transmitter (not recommended).

     6.   Additional sensors  (for  measuring line temperature and
          pressure) and a module for calculating gas flow  in
          standard units.
                            86

-------
Installation

1.   Primary system.

     a.   Mount the orifice plata in either horizontal or
          vertical process piping.  Pressure tap locations
          and AP transmitter locations will differ according
          to the orientation selected.

     b.   Install beveled or cut away plates (Figure  3.1)
          with the flat surface upstream.

     c.   Use 1.6 millimeter (1/16 in) thick gaskets,
          graphited on the side next to the plate.  The
          gaskets must not extend into the pipe or obstruct
          vent and drain holes (if used).

     d.   Provide straight run smooth piping upstream and
          downstream of the orifice plate.  The length of
          straight run required depends on the Beta ratio.
          Recommended lengths are shown in Figure 3.3.  Use
          straightening vanes when it is not practical to
          install the meter with the recommended straight
          pipe length.

     e.   Pressure taps should be free of any burrs or
          protrusions into the pipe.
                       87

-------
                                                                           -jof
                      o    020   040   ota   tuo
                           DIAMETER RATIO,/9
                 (A) FOR ORIFICES AND FLOW NOZZLES
                    ALL FITTINGS IN SAME PLANE
    0   Om  040   06O  O«0
          DIAMETER RATIO,/)
(B) FOR ORIFICES AND FLOW NOZZLES
   ALL FITTINGS IN SAME PLANE
                                                                                   ORIFICE OR FLOW NOZZLE.
 10
OIAM

 -
                                                                                        -
                                                                                      /

                                                                                      )
                                                                                       ELLS,TUBE TURNS OH
                                                                                       LONG RADIUS BENDS
   (U) ORIFICE OH FLOW NOZZLE


    ^tm. c J^k   tf
    S~\--\— A	»1     | IS
 2DIAM    '             -I-^A
 ""    STRAIGHTENING     •
      VANE 2DIAM.LONG
    0   020   040   OCO   0-80
          DIAMETER RATIO,/)
(C) FOR ORIFICES AND FLOVV NOZZLES
  FITTINGS IN DIFFERENT PLANES
                                                                        020  04O  O6C  080
                                                                          DIAMETER RAflO./)
                                                                (D) FOR ORIFICES AND FLOW NOZZLES
                                                                   FITTINGS IN  DIFFERENT PLANES
00
00
                          OAIFICE OR FLOW NOZZLE.

                                       ^
                      0    020   040   060   060
                            (KAUETER RATIO, 0
                 (E) FOR ORIFICES AND FLOW NOZZLES
                    WITH REDUCERS AND EXPANDERS
                                                                                        .Baffin
    0    020   040   060   OM
          DIAMETER RATIO, />

(F) FOR ORIFICES AND FLOW NOZZLES
   IN ATMOSPHERIC INTAKE
       020   040   aw   0*0
         DIAMETER RATIO, £

 (G) VALVES AND REGULATORS
                                                  FIG. ll-II-l  RECOMMENDED MINIMUM LENGTHS t P I'IPE PIIUCEDING
                                                            AND fOLLOHlNG ORIFICES. FLOW NOZZLES AND
                                                            VENTUIII TUBES (ALL CONTIIOL VALVES. INCLUDING
                                                            REGULATORS, SHOULD HE LOCATED ON OUTLET SIDE
                                                            OF PRIMARY ELEMENT.)
                                                                *jto   oto  o«o   040   oeo
                                                                      DIAMETER RATIO,/)

                                                                  (H) FOR VENTURI TUBES

-------
2.    Secondary system.

     Installation of the secondary system  (pressure
     connections, tap line run, and Ap transmitter location)
     differs between applications for steam flow
     (condensible) and gas flow measurement.

     a.   Steam flow measurement.

          1)   A typical installation diagram  is shown  in
               Figure 3.4.

          2)   Always use condensing chambers  on tap  line
               runs.  Mount each chamber at the same  level.

          3)   Install horizontal portions of  tap line  runs
               so they slope downward from the orifice  at  a  1
               in 12 grade.

          4)   Install the AP  transmitter below the orifice
               plate location  for both vertical and
               horizontal piping runs.

          5)   If the transmitter must be mounted above the
               pressure connections either vena contracta  or
               pipe taps are recommended.  Flange taps  are
               not recommended.
                        89

-------
CONDENSING
CHAMBERS -
 PLUGGED
  TEES
                                                DIFFERENTIAL
                                                PRESSURE
                                                TRANSMITTER
 PLUGGED   i>  SLOPE ALL HORIZONTAL
  TEES       RUNS AT LEAST l" PER I'-O"
         Figure  3.4.   Steam flow installation.

         b.    Gas flow measurement.

              1)   A typical  installation diagram is shown in
                   Figure  3.5.

              2)   Mount the AP transmitter  above the orifice
                   plate for  both vertical and horizontal piping
                   runs.

              3)   If the  gas is corrosive,  use a liquid seal
                   with diaphragm pressure connections to isolate
                   the transmitter.

              4)   Install horizontal portions of tap line runs
                   so they slope upward from the orifice at a 1
                   to 12 grade.
                            90

-------
    3 -VALVE
    MANIFOLD
                            DIFFERENTIAL
                            PRESSURE
                            TRANSMITTER
        SLOPE ALL HORIZONTAL
        RUNS AT LEAST l" PER l'-0"
              ,,	^—TO TRANSMITTER
                       -TO ORIFICE
PLUGGED A '
TEES-" x
N
N
x i
^
* >
"N *
U^
r^ b
V
^
*
^
                      -DRIP POTS
                       INSTALL WHEN TRANSMITTER
                       HAS  TO  8E MOUNTED  BELOW
                       THE  PRESSURE TAPS
Figure 3.5.  Gas flow installation.
                    91

-------
     3.    Additional recommendations.

          a.   Locate the transmitter to facilitate easy access
               for calibration and maintenance.

          b.   Tap line runs should not exceed 15 m  (50 ft) and,
               if freezing is possible, should be insulated or
               heated.

          c.   Take special care to mount  theAp transmitter
               pressure connection plumbing  so the differential
               neasurement is not affected.

          d.   An isolation valve manifold and quick disconnects
               should be installed in the  tap  lines  to  facilitate
               sensor calibration.

G.   Designer Checklist

     Use the following checklist when designing or reviewing
     orifice plate gas flow meter applications.  All checklist
     items should be verified affirmative  for proper application
     and installation.

     1.   General items.

          a.   Is the process gas or steam recommended  in  Table
               3.1?

          b.   Is a large head loss acceptable?

          c.   Is the Reynolds number at minimum flow greater than
               10,000?

          d.   Has  the proper orifice size based on  Beta  ratio,
                (d/D ratio) been determined for the expected  flow
               range  and allowable pressure  loss?

          e.   Is the Beta ratio greater  than  0.2 and less than
               0.7?

          f.   Will  the  meter construction materials withstand the
               corrosive properties  of  the fluid  to  be  measured?

          g.   Has  the proper differential range  been  selected for
               theAp transmitter?

          h.   Have the  flange gaskets  been  properly sized to
               insure no protrusion  into  the inside  diameter of
               the  process i pipe?
                             92

-------
          i.    Does the straight run piping conform to the minimum
               requirements in Figure 3.4?

          3.    Are the tap line runs less than 15 m (50 ft)  long?

          K.    If freezing is possible, are the tap lines
               adequately insulated or heated?

          1.    Has an isolation valve manifold and quick
               disconnects been installed in the tap lines to
               faciliate &p sensor calibration?

          m.    Will the Ap sensor be mounted in a vibration  free
               location?

     2.   Steam flow measurement.

          a.    Have condensing chambers been provided  in  the tap
               lines and are they of adequate size?

          b.    Is the transmitter mounted below the process
               connections?  If it is not,.have either vena
               contracta or pipe taps been used rather than  flange
               taps?  Insulate from thermal shocks with tube loop
               (pig tail) or other means.

     3.   Gas flow measurement.

          a.    Is the transmitter mounted above the process
               connections?

          b.    Have condensata traps been installed at the lowest
               point of the tap line runs?

          c.    If the gas is corrosive, have diaphragm sealed
               pressure connections been provided?

H.   Acceptance and Performance Monitoring

     Recommended acceptance testing and performance monitoring
     procedures are described in Section 7.2 related to:

     1.   Verification of manufacturer accuracy and factory
          calibration documentation.

     2.   On-site testing.

I.   Maintenance and Calibration

     1.   Primary system  (orifice assembly).

          a.   Test the primary with a portable manometer monthly.
                             93

-------
          b.   If accuracy problems persist, remove orifice  plate
               and inspect orifice for solids buildup and/or wear.

     2.   Secondary system (Ap sensor).

          a.   For gas flows, empty condensate traps once per  week.

          b.   Recalibrate transmitter monthly using a portable
               manometer or other suitable calibration test  set.

J.   Deficiencies

     The following problems are commonly encountered with existing
     orifice plate gas flow meter applications.

     1.   Orifice oversized  (Beta ratio too high) thus generating
          a differential too low to be accurately "monitored  by
          the Ap transmitter provided.

     2.   Orifice properly sized, but the wrong _\p sensor range
          was selected.
                                      •
     3.   Condensate traps not provided, causing water
          accumulation and occasional freezing in the lines.

     4.   Unequal tap line lengths or elevations, causing
          differential measurement errors.

     5.   Insufficient straight run piping provided.

     6.   Insufficient calibration of primary and secondary
          systems.

K.   References

     1.   Liptak, B. G. and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement.  Chilton Book Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.

     2.   Fluid Meters, Their Theory and Application.  Report of
          ASMS Research Committee on Fluid Meters, American
          Society of Mechanical Engineers, 345 East 47th Street,
          New York, New York, 1971, 6th Edition.

     3.   The Foxboro Company.  Technical Bulletins 6-110, 7-110,
          7-251.   Foxboco, Massachusetts.
                            94

-------
4.   Instrument Society of America.  Flange Mounted Sharp
     Edged Orifice Plates for Flow Measurement.
     ISA-RP3.2-1978.  Research Triangle Park, NC.

5.   American Petroleum Institute.  Manual on Installation of
     Refinery Instruments and Control Systems.  Part 1 -
     Process Instrumentation and Control.  Section 1 - Plow.
     API RPS50, Washington, DC, 1977, 3rd Edition.

6.   Henson, J. S.  Process Instrumentation Manifolds.
     Instrument Society of America, Research Triangle Park,
     NC., 1981.

7.   Spink, L.K.  Principles and Practice of Flow Meter
     Engineering.  The Foxboro Company, Foxboro, MA, 1967,
     9th Edition.

8.   Cusick, C. F.  Flow Meter Engineering Handbook.
     Honeywell, Inc., Fort Washington, PA, 1977, 3rd Edition.

9.   Sprenkle, R. E.  Piping Arrangements For Acceptable Flow
     Meter Accuracy.  ASME Transactions 55:345, New York, NY,
     1945.

10.  Starret, P. S., Halfpenny, P. F. and Noltage, H. 3.
     Survey of Information Concerning the Effects of
     Nonstandard Approach Conditions Upon Orifice and Venturi
     Meters.  Paper presented at Annual Winter Meeting,
     American Society of Mechanical Engineers, New York, NY,
     1965.
                       95

-------
3.2  VENTURI TUBES AND FLOW TUBES

     A.   Applications

          General conditions which are  suitable  for  the application of
          venturi and proprietary flow  tube gas  flow meters:

          1.   The Reynolds number of the  process  stream at the meter
               is greater than 150,000.

          2.   A meter rangeability of  4:1 is  acceptable.
              TABLE 3.2.  VENTURI TUBES AND  FLOW  TUBES
                             APPLICATION GUIDELINES
               Recommended
                                           Not Recommended
                                         Any  low-pressure (uncompressed)
                                             gas  flows
Boiler steam
Compressed digester gas
Incinerator draft/blower air
Air flow
Oxygen flow
Corrosive gasses
     3.   Principle of Operation

          1.   Venturi tube.

               A venturi tube operates  on  the  principle that a gas
               flowing through a meter  section containing a convergence
               and constriction of  known shape and area will cause a
               pressure drop at the constriction area.   The difference
               in pressure between  the  inlet and the constriction area
               (throat) is proportional to the square of the flow
               rate.  Figure 3.6 shows  a cut-away of a typical venturi
               tube.
                           -HIGH PRESSURE TAP

                                       •LOW PRESSURE TAP
               INLET
                  INLET CONE -/                   ^OUTLET CONE


                 Figure  3.6.  Classic venturi tube.
                                  96

-------
2.   Flow tube.
          Several manufacturers  provide  differential-causing flow
          tubes that are modified  versions of the classical
          venturi tube.  These devices operate on the same
          principle as the classical  venturi; however, they
          provide features which make them more attractive for
          some applications,  i.e., less  space is required for
          installation and overall head  loss is reduced.  Figure
          3.7 shows three commonly used  flow tubes.
                    GENTILE OR BETHLEHEM
                        FLOW TUBE
                      LO-LOSS FLOW TUBE
                         CALL TU3E
            Figure 3.7.  Proprietary flow  tubes.
                             97

-------
     3.   Pressure sensing.

          Both the venturi tube and the proprietary flow tubes are
          primary elements and require a secondary element to
          sense the pressure differential and convert it to a
          usable signal.  The secondary element in most
          applications is a differential pressure  (A?) transmitter.

          The A p produced by a flow tube is representative of the
          volumetric flow rate at the actual operating temperature
          and pressure.  Appropriate temperature and pressure
          sensors are required to correct the transmitter output
          to standard reference conditions.

          The AP in the tube is measured at the inlet and throat
          (Figure 3.6).

          One AP measurement method uses single connections in the
          inlet and throat of the tube.  The pressure tap lines
          are coupled directly to the tap holes and run to the AP
          transmitter.

          As an alternative method, piezometric rings may be used
          to sense inlet and throat pressures.  These consist of
          several holes around the circumference of the tube at
          the inlet and throat tap locations.  Each set of holes
          is connected to an annulur ring to give  an average of
          the pressure at each tap hole connected  to the ring.
          Piezometric rings are usually used in large diameter
          tubes to minimize velocity profile skewing.

C.   Accuracy and Repeatability

     The accuracy and repeatability of these meters vary with the
     type used.  The characteristics of the secondary element
     (transmitter) must also be included in the total accuracy
     figure.  The following limits can be expected when
     considering these types of flow meters for applications
     previously listed:

     Accuracy:               +1% of actual flow.

     Repeatability:          +1% of actual flow.

     The values shown are 'jr a complete system  (primary and
     secondary) when properly applied and installed.  Factors
     which will degrade these levels during operation include:
     improper tube sizing, improper AP range, insufficient
     straight pipe before and after the meter  (see Part F,
     Designers Checklist) and piping elements which disrupt  the
     velocity profile  (see Part E, Installation).

     Venturi tubes, flow tubes, and flow nozzles are all capable
     of exceeding the accuracy values shown.  Consult the
     manufacturer if greater accuracy is required. Caution:  both
     the primary and secondary element must be considered when
     designing for optimum accuracy.

                            98

-------
E.
Manufactured Options

1.   Primary metar tube.

     a.   Single sensing ports.

     b.   Piezometer ring sensing.

     c.   Inspection openings.

     d.   Manual rodders for cleaning sensing ports.

2.   Secondary element  (transmitter).

     a.   Differential pressure transmitter  (see Section  6.2)

     b.   Manometer transmitter (not recommended).

     c.   Temperature and pressure correction system

Installation

1.   Primary system.

     a.   Venturi and flow tubes may be  installed  in  any
          position to suit the requirements  application;
          however, the primary and secondary system must  be
          accessible for maintenance and calibration.

     b.   Plow disturbing obstructions,  pipe fittings and
          valves will produce meter inaccuracies and  should
          not be located too near the metar  inlet.  Use
          Figure 3.3 is to determine the minimum upstream
          distance of straight pipe recommended between
          fittings and the meter inlet.
3IHO
- — m — =
^fc
-flfcxfTT" — fl
0"~* fl
	 1
— — n
— — — i
T 	
-ilrHU 	 w 	
J— 12-
DIA
^
VENTURI
A
rfTK
w
VENTURlTT



<±±
TWO ELBOWS NO
IN SAME _ PLANE,
PARTIALLY
' THROTTLED
-GATE VALVE
. GLOBE UALV
CHECK VALV1
































£~


^
E,
E


1
^
*^
•=


^x
/
i

/
^ ^

~—

r
**,

1
/^


/

i^

»—

1
1



V
y

,
A

*B









s

*•









s



-------
     c.   If a flow control valve is required  in  the  line,  it
          should be placed downstream from the meter  tube as
          shown in Figure 3.8.  .

     d.   Locate all downstream pipe fittings a minimum
          distance of two pipe diameters downstream of tire
          throat tap(s).

     e.   Install the primary and secondary flow  elements in
          an accessible location with suitable space  provided
          for maintenance and calibration.

2.   Secondary system.

     Installation of the secondary system (pressure
     connections, tap line run, andAp transmitter location)
     differs between applications for steam.flow
     (condensible)  and gas flow measurement.

     a.   Steam flow measurement.

          1)   The tap lines are normally flooded with
               condensate.

          2)   Use condensing chambers on tap line runs.
               Mount each chamber at the same level.

          3)   Slope horizontal tap line runs downward from
               the pressure  taps at a 1 in 12 grade.

          4)   Install the ^p transmitter below the process
               pipe for  horizontal runs, or  below the
               pressure  connections for vertical runs.

          5)   A. typical installation diagram is shown in
               Figure 3.9.
                      100

-------
     CONDENSING
     CHAMBERS -
  PLUGGED
    TEES
                                                DIFFERENTIAL
                                                PRESSURE
                                                TRANSMITTER
                                              PIPE
                                              STAND
     PLUGGED
      TEES
                SLOPE ALL HORIZONTAL ,
                RUNS AT LEAST l'  PER I-0'
Figure 3.9.   Steam flow measurement  installation diagram.

          b.   Gas flow measurement.

               1)   The tap lines are normally  dry.

               2)   Mount the AP transmitter  above the process
                    pipe  for horizontal runs, or  above the
                    pressure connections for  vertical runs.

               3)   If  the gas is corrosive,  use  a liquid seal
                    with  diaphragm pressure connections to isolate
                    the transmitter.

               4}   Slope horizontal tap line runs upward from the
                    pressure taps at a 1 and  12 grade.

               5)   A typical installation diagram is shown in
                    Figure 3.10.
                            101

-------
                      3-VALVE
                      MANIFOLD
                                                  DIFFERENTIAL
                                                  PRESSURE
                                                  TRANSMITTER
                      SLOPE ALL HORIZONTAL
                      RUNS AT LEAST l" PER l'-0"
  PLUGGED V
    TEES -- - -
                \
                        TO ORIFICE
                  \
                    \
                     \
                                       TO TRANSMITTER
                                *-
                             hsJ     INSTALL WHEN TRANSMITTER
                                     HAS TO BE MOUNTED BELOW
                                     THE PRESSURE TAPS
Figure 3.10.   Gas  flow measurement installation diagram.
                              102

-------
     3.    Additional recommendations.

          a.    The transmitter should be located to facilitate
               easy access for calibration and maintenance.

          b.    Tap line runs should not exceed 15m  (50 ft.)  in
               length.

          c.    If a freezing potential exists, heat trace  and
               insulate the tap lines.

          d.    Mount the transmitter so that the high and  low
               pressure connections are at exactly equal
               elevation.  Failure to do so will create a  bias  in
               the indicated AP which will in turn introduce an
               error in flow measurement.

          e.    An indicator guage  (AP) should be placed near the
               primary element for convenience in calibration and
               performance monitoring  (usually mounted on  the
               secondary element).

          f.    The Beta ratio and overall diameter of the  flow
               tube should be carefully determined for the
               expected flow range.  Accordingly, the range  of
               the AP transmitter must match that of the flow tube
               over the expected flow  range.

F.   Designer Checklist

     Use the following checklist when  designing or reviewing
     orifice plate gas flow meter applications.  Answer all
     checklist items with a yes for proper application and
     installation.

     1.   Is the process gas or steam  recommended in Table 3.2?

     2.   Is the Reynolds number greater than 150,000?

     3.   Has the primary element  been properly sized to generate
         • a suitable differential pressure over the range  of the
          expected flow?  Bear in mind that meter sizing for 20
          year projected flow typically results in oversizing.

     4.   Has the proper differential  range been selected  for  the
          secondary device?

     5.   Has adequate straight run piping been provided both  up
          and downstream?

     6.   Are the tap lines sloped properly?

     7.   If measuring steam flow;  is  the transmitter installed
          below  the process connections, and have condensing
          chambers been provided  in  the tap lines?

                            103

-------
     8.   Are the tap line runs less than 15m  (50  ft)?

     9.   Is freezing a possibility?  If so, are the tap  lines
          heated and insulated?

     10.  Are both the primary and secondary systems readily
          accessible for maintenance?

     11.  When metering gas flow; is tne transmitter installed
          above the process connections?

     12.  When metering gas flow; have condensate  traps or drip
          legs been installed at the low point of  the tap line
          tuns?

G.   Maintenance and Calibration

     1.   Primary system.

          a.   If performance monitoring indicates a large
               accuracy loss, test the primary with a portable
               manometer.

     2.   Secondary system.

          a.   Bleed off condensate in the tap lines regularly.

          b.   Zero and recalibrate transmitter monthly using a
               portable manometer.

H.   Deficiencies

     The following problems are commonly encountered with existing
     venturi and flow tube applications:

     1.   Meter oversized.  Low flow differentials are lost due to
          square root function cut-off.

     2.   Gas buildup caused by tap lines that are not properly
          sloped and/or not equipped with bleed valves.

     3.   Improper differential range selection for the £.p
          transmitter.

     4.   Tap lines are plugged or restricted.

I.   References

     1.   Liptak, B. G. and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement.  Chilton Book  Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.
                            104

-------
         2.   Spink, K. L. Principle and Practice of Flow Meter
              Engineering.  The Foxboro Co.,  Foxboco, Massachusetts,
              1967, 9th Edition.

         3.   Water Pollution Control Federation.  Instrumentation in
              Wastewater Treatment Plants, WPCF Manual of Practice No.
              21, 1978.
3.3  AVERAGING  PITOT TUBES

     A.    Applications

          The following general conditions are suitable for the
          application of  averaging pitot tubes:

          1.    Clean gas  or  steam (free of solids),

          2.    Minimize head loss, and

          3.    An acceptable meter rangeability of 3:1.


      TABLE 3.3.   AVERAGING  PITOT TUBES APPLICATION GUIDELINES
               Recommended
                                         Not Recommended
                                       Gas or steam with particulace
                                         solids
                                       Low pressure (uncompressed
                                         digester gas)
                                       Corrosive gases
Boiler steam
Compressed digester gas
Natural gas
Activated sludge treatment
  - blower air
  - oxygen
Incinerator draft/blower air
Aerated grit chamber,  air flow

B.   Principle of Operation
          Averaging  pitot  tubes are differential producing flow
          measuring  devices  that consist of an insertion probe with
          multiple upstream  sensing ports and a single downstream
          static port.   The  probe  is geometrically constructed such
          that an average  upstream pressure is measured.  Figure 3.1
          shows the  probe.
                               105

-------
/w» ^x
FOR EQUAL /VV"*
ANNULAR
AREAS
/w—
/
/w*. ^^/
*///////

\

1
s
VELOCITY
AVERAGE
SENSING
(TYPICAL
CF FOUR)

/ / / S / / J
\


c
5
>
-v



J
X.
/




,/



V
X1



Jt,
S
{


STATIC
PORT

////// /S///S/S
Figure 3.11.   Pitot tube probe.
            106

-------
     The averaging pitot  tube, like the venturi meter is a primary
     sensing element  that creates a pressure differential
     proportional to  the  square of the flow rate.  Like the
     venturi,  a £P cell is used to measure the differential
     pressure and convert it to a voltage or current signal.   A
     secondary element to convert the nonlinear differential  into
     a linear flow rate is required.  In most cases, this device
     is a square root extractor.

C.   Accuracy and Repeatability

     The accuracy and repeatability of the averaging pitot tube is
     good; however, the characteristics of the&p transmitter and
     square root extractor must be included in the total accuracy
     figure.  The following performance limits are attainable by
     averaging pitot  tubes for the previously recommended
     applications:

     1.   Accuracy:          +1.0 to 3% of full scale.

     2.   Repeatability:     +1.0% of full scale.

     These accuracy levels reflect optimum values achievable  for
     proper application and installation.  Factors that will
     degrade these  levels include operation at actual flows
     outside the  expected flow range, and piping elements that
     disrupt the  velocity profile.

D.   Manufactured Options

     1.   Mounting:

          a.   Mounting coupling,

          b.   Flange, and

          c.   Hot  tap.

     2.   Secondary element:

          a.   Differential pressure transmitter (standard),  and

          b.   Manometer  transmitter  (not recommended).

     3.   .Calculation modules for standard pressure, temperature
          correction  and  linearization  to flow units.

B.   Installation

     1.   Primary system.

          a.   Mount  the  averaging pitot tube in either horizontal
               or vertical process piping.  However, the  tap line
               configuration  and Ap transmitter locations will
               differ.

                         107

-------
        b.   Install the probe with the multiple  ports  facing
             upstream.

        c.   Provide adequate straight-run smooth piping
             upstream and downstream of the pitot tube.  When  it
             is not practical to install the pitot tube with the
             recommended straight pipe length,  use straightening
             vanes.  Recommended lengths with and without  vanes
             are shown in Figure 3.12.
MINIMUM
DIAMETERS
OF
STAIGHT PIPE1
°~
% , 'alfl

o
fJrci"c-iDid
o
«i— A— LB$
-O-
«&fc£J2=L«jl
P ?
' ( 	 A 	 U-lB
P -9- 1
tS-TSteJ* '
rr + ,-n
^U_A_LaJ^
ft* * --n '
Ss.Ttso.r
Y
CLJ I i:n
1— A— Ul
f
'-U—.H I.,,.!-1-1
tS.TfcSd.BJ
Hi ? ,
t»J i 1
1 	 * — 1-8-1 SEE-
tl) ^ NCTTE
n=s*tij 2
UPSTREAM DIMENSION
WIT>
var
= IN
s
A
7

9

19

8

8

24

HOUT
JES
OUT
s
9

14

24

8

8

24

WITH
VANES
A LP

6

a

9

8

8

9

W

4

4

4

4

4
C

3

4

5

4

4

5
DOWNSTREAM
DIMENSION
B'
3
3
4
3
3
4
Figure 3.12.   Typical  upstream/downstream requirements.

    2.   Secondary systems.

        Installation of the secondary system (pressure
        connections, tap line run, and AP transmitter location)
        differs oetween applications for steam flow
        (condensible)  and gas flow measurement.

        a.   Steam flow measurement.

             1)   A typical installation diagram is shown in
                  Figure 3.13.
                          108

-------
             2)   Always use condensing chambers on tap  line
                  runs.  Mount each chamber ac  the same  level.
                  Size condensation chambers  large enough  for
                  the application.  This  is to  prevent flooding
                  between routine maintenance checks.

             3)   Install horizontal portions of tap  line  runs
                  so they slope upward from the primary  element
                  at a 1 in 12 grade.

             4)   Install the &p transmitter  below the process
                  pipe for horizontal piping  runs, below the
                  pitot tube location for  vertical piping  runs.
    HORIZONTAL LINE (HL)
 VERTICAL LINE (VL)
  5 VALVE
 MANIFOLD
    LOW DISPLACEMENT
     DP TRANSMITTER
  (NON-MOTION BALANCE)
                   = TO REMOTE OR
                     LOCAL READOUT
                     RECORDER OR
                     CONTROLLER
ANNUBAR INSTRUMENT CON-
NECTIONS V/ILL BE POSITIONED
90° FROM STANDARD.
Figure 3.13.  Installation for steam flow applications.

         b.    Gas  flow measurement.

              1)    A typical  orientation  diagram is shown in
                   Figure 3.14.

              2)    Mount the AP  transmitter above the process
                   pipe for horizontal piping runs, above the
                   pitot tube for vertical piping runs.

              3)    Install horizontal portions of tap line runs
                   so they slope upward at a minimum of a 1  in
                   12 grade.
                       109

-------
Figure 3.14.    Orientation for gas flow applications.

   3.   Additional recommendations.

       a.   Locate the transmitter  to facilitate easy  access
            for calibration and maintenance.

       b.   Tap line runs should not exceed 15 m (50 ft)  and,
            if freezing is possible, should be insulated.

       c.   Mount the transmitter so that the high and low
            pressure connections are at exactly equal  elevation.

       d.   Provide a 3-valve manifold and quick connects for
            connecting a manometer  during calibration.

   Designer Checklist

   Use the following checklist when  designing  or reviewing pitot
   tube gas flow meter applications.   All checklist items  should
   be verified affirmative for proper application and
   installation.

   1.   General items.

       a.   Is the process gas or steam recommended  in Table
            3.3 and free of particulates?

       b.   Has the proper differential pressure range been
            selected for the secondary device, i.e., AP
            transmitter?

       c.   Has adequate straight-run piping  been provided to
            conform to the minimum  requirements in Figure 3.12?
                      110

-------
          d.    Do  the horizontal tap line runs slope upward at a
               minimum of  a  1 to 12 grade?

          e.    Are the tap line runs less than  5M (15 ft) long?

          f.    If  freezing is possible, are the tap lines
               insulated and heat traced?

          g.    Have a 3-valve manifold and quick disconnects for a
               manometer been provided for calibration?

          h.    Will the meter be mounted in a vibration free
               location?

     2.    Steam flow measurement.

          a.    Have condensing chambers been provided in the tap
               lines and are they of adequate size?

          b.    Is  the transmitter mounted below the process
               connections?

     3.    Gas flow measurement.

          a.    Is  the transmitter mounted above the process
               connections?

          b.    Have condensate traps been installed at the lowest
               point of the  tap line runs?

G.   Acceptance and Performance Monitoring

     Provide  for acceptance  testing and performance monitoring as
     described in  Section  7.2, related to:

     1.    Hydraulic testing.

     2.    Verification of  manufacturer accuracy and factory
          calibration and  documentation.

H.   Maintenance and Calibration

     1.    Primary  system.

          a.    When performance monitoring indicates a large
               accuracy loss, test the primary with a portable
               manometer.

          b.    Extended periods of poor accuracy:  remove pitot
               tube and  inspect orifice for solids buildup and/or
               wear.
                        Ill

-------
     2.   Secondary system.

          a.   For gas  flows,  empty  condensate traps once a week.

          b.   Check the transmitter calibration monthly using a
               portable manometer  or other suitable calibration
               test set.

I.   Deficiencies

     The following problems  are  commonly encountered with existing
     pitot tube gas flow meter applications.

     1.   The wrong range on the AP  transmitter was selected.

     2.   Condensate traps were  not  provided, causing water
          accumulation  and occasional freezing in the lines.

     3.   Unequal tap line lengths or elevations used, causing
          differential  errors.

     4.   Insufficient  straight-run  piping provided.

     5.   Infrequent maintenance.

J.   References

     1.   Liptak, B. G. and  X. Venczel.  Instrument Engineers
          Handbook of Process  Measurement.  Chilton Book Company,
          Radnor, PA, 1969,  Revised, 1982.

     2.   Considine, D. M.   Process  Instruments and Controls
          Handbook.  McGraw  Hill Book Company, New York, NY, 1974.
                        112

-------
3.4  TURBINE FLOW METERS

     A.   Application

          General conditions which are suitable for turbine meters  to
          measure gas flow include:

          1.   An intermittent flow may be expected.

          2.   A maximum meter rangeability of 15:1 is acceptable.

       TABLE  3.4.   TURBINE FLOW METER APPLICATION GUIDELINES

               Recommended                     Not Recommended	
     Steam                              Low pressure '(uncompressed)
     Compressed digester gas              digester gas
     Natural gas

     B.   Principle of Operation

          Turbine flow meters consist of a pipe  section with  a
          multi-bladed rotor suspended in the fluid stream  on a  free
          running bearing, see Figure 3.15.  The,plane of rotation of
          the rotor is perpendicular to the flow direction  and the
          rotor blades sweep out nearly to the full bore of the  pipe.
          The rotor is driven by the process gas impinging  on the
          blades.  Within the linear flow range  of the meter, the
          angular velocity of the rotor is directly proportional to the
          liquid velocity which is  in turn, proportional to the
          volumetric flow rate.  The speed of rotation is sensed by an
          electromagnetic pickup coil which produces a pulse. | The
          output signal is a continuous voltage  pulse train with each
          pulse representing a discrete volume of gas.  The turbine
          output frequency is proportional to the volumetric  flow  rate
          at the actual operating temperature and pressure.  An
          appropriate temperature and pressure correction system is
          required to convert the meter output into a volumetric rate
          at standard reference conditions.
                              113

-------
                     PICXUP COIL
       UPSTREAM
                ROTCR
                 UNIT
               ASSEMBLY
      HANGER UNIT
                                        HOUSING
                                  SPINDLE
                                            DOWNSTREAM
                                              HANGER
                                               UNIT
C.
0.
        Figure  3.15.  Gas  turbine meter.

Accuracy and Repeatability

When properly applied and  installed, the accuracy and
repeatability characteristics of turbine flow meters, should
be:
     1.   Accuracy:


     2.   Repeatability:
                         +0.25% of actual flow, within  the
                         linear range of the meter.

                         +0.05% within the linear range of  the
                         meter.
Each turbine flow meter  has a unique "K" factor  (the number
of pulses generated  per  unit volume) which is determined
during factory  flow  calibration.  This factor and thus  the
accuracy of the meter,  is affected by mechanical wear.

Manufactured Options

1.   Wetted parts materials.

     a.   Stainless  steel (standard).

     b.   Hastelloy  "C".

     c.   Teflon bearings.

2.   Flow straightening  vanes.

3.   Additional electromagnetic pickup and associated
     electronics for increased accuracy.
                          114

-------
     4.    Pressure  and  temperature correction system for
          calculating volumetric flow under standard conditions.

     5.    Turbine meters  require secondary elements for indicating
          flow at the meter or retransmitting for remote
          monitoring.   It  is suggested these elements be purchased
          from the  same manufacturer.  If another supplier is
          used, take care  to ensure that both units are compatible
          with regard to signal pulse shape/ amplitude, width, and
          frequency.

          Typical secondary elements include:

          a.    Electromechanical rate indicator and totalizer.

          b.    Pulse-to-current signal converter-.

          c.    Signal pulse preamplifier (for long distance pulse
               signal transmission).

E.    Installation

     1.    Piping obstructions which severely disturb the flow
          profile severely affect turbine meter accuracy.  Figure
          3.16 shows recommended piping installation including
          flow straightening vanes.

     2.    Turbine meters have a linear flow relationship.  They
          are sized by  volumetric flow rate.  Use the following
          guidelines when  sizing a turbine meter:

          a.    Each meter  size has a specified minimum and maximum
               range of flow linearity and should not be used for
               flow rates  outside that range.

          b.    The  maximum flow rate for the application should be
               70%  to 90%  of the maximum flow rate specified for
               the  meter.

          c.    Size the meter on actual volume flow and not on
               reference or standard units.

          d.    The  meter size should be less than the diameter of
               the  process piping.

          e.    Available turbine meter sizes range from 0.5 - 60.0
               cm (3/16 to 24 inches) in diameter.
                        115

-------
3.    The recommended minimum upstream straight-run  for
     optimum accuracy  is  25  to 30 pipe diameters.   If
     necessary, this distance may be reduced to 10  pipe
     diameters by installing straightening vanes.   The
     following pipe fittings produce flow disturbances that
     will degrade meter accuracy if placed closer than the
     specified distances.
a.
b.
c.
d.
e.
Valves,
Gates ,
Tees,
Elbows ,
Severe i



and
redu<
          Severe reducers  and expanders (>30 degrees
          included angle).
 CONCENTRIC
   CONE
                        NOMINAL SIZE
                                            CONCENTRIC
                                              CONE
      ALTERNATIVE FLOW
     STRAIGHTENING VANES
                          METER a STRAIGKTENER
                             CONNECTIONS
4.
  Figure 3.16.  Meter installation.

Locate downstream  piping obstructions at least  5  pipe
diameters'from the meter.
5.   Use shielded  cable between the turbine meter  and
     secondary electronics.

6.   Route power wiring and signal cable  in separate conduit.
                     116

-------
F.   Designer Checklist

     The following checklist should be used when designing  or
     reviewing turbine flow meter applications.  All checklist
     items should be answered affirmative for proper application
     and installation.

     1.   Is the intended process gas recommended  in Table  3.4?

     2.   Can the expected head loss be tolerated?-

     3.   Are all pipe obstructions located a minimum  upstream
          distance of:

          a.   10 pipe diameters when flow straightening  vanes  are
               used?

          b.   25-30 pipe diameters without flow straightening
               vanes?

     4.   Is there a minimum downstream distance of  5  pipe
          diameters to any flow disturbing fittings?

     5.   Has the proper secondary flow indicator/signal
          conditioner been provided?

     6.   Is power available for the secondary  element?

     7.   Is the meter accessible for maintenance?

     8.   Is the meter diameter smaller than  the process  piping?

     9.   If temperature and pressure correction are desired, have
          provisions been made?

G.   Maintenance and Calibration

     The meter constant "K" is determined at  the manufacturer's
     facility prior to meter shipment and is  performed under
     standard conditions.  If the intended application process  gas
     has significantly differing physical characteristics,  the
     manufacturer should be consulted for additional testing data.

     Turbine meters do not require calibration, but  periodic
     calibration may be required on  the secondary  element.   When
     meter accuracy becomes questionable  (as  observed  through
     performance monitoring) check the  "K" factor  by physical
     testing.
                         117

-------
H.   Deficiencies

     The following problems are commonly encountered with existng
     turbine raeter applications:

     1.   Inadequate upstream and downstream straight run piping,
          resulting in poor meter accuracy.

     2.   Meter sized too large, resulting in poor accuracy at low
          flows.

     3.   Mett=i and secondary element are not compatible because
          of differing electrical specifications.

     4.   Although rare, the factory determined "K" factor is
          incorrect.

I.   References

     1.   LiptaK/ B. G. and Venczel, K. Instrument Engineers
          Handbook of Process Measurement.  Chilton Book Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.

     2.   Foxboro Company.  Technical Bulletin No. TI, 16-6a.
          Foxboro Company, Foxboro, Massachusetts, January, 1971.
                          118

-------
4.0  FLOW MEASUREMENT, OPEN CHANNEL


     4.1  KENNISON NOZZLE

          A.   Application
               The Kennison nozzle is a proprietary product designed to
               measure flow only in partially filled pipes.  Kennison
               nozzles are designed to flush through solids without
               accumulation and are generally considered to have a maximum
               to minimum measurement ratio of 10 to 1.  A Kennison nozzle
               would be selected for flow measurement only when all of  the
               following general conditions apply:

               1,   Pipe size is not smaller than 0.15 m (6 in) nor larger
                    than 0.9 m (36 in).

               2.   The pipe does not flow full.

               3.   High and low operating flows fall respectively within
                    the 100% and 10% capacity of the desired nozzle size.

               4.   The level of the liquid downstream will always be below
                    the bottom of the nozzle so that free discharge exists.
       TABLE  4.1.   FLOW MEASUREMENT,  OPEN  CHANNEL APPLICATION GUIDELINES

          	Recommended	   	Not Recommended	

          Raw sewage                         Pilled lines
          Partially filled lines


          B.   Principle of Operation

               The Kennison nozzle is a constriction to liquid  flow  of  known
               geometry which will produce a hydraulic head  at  the area of
               the constriction.  When the nozzle  is operating  above minimum
               flow rate (10% of the maximum nozzle flow)  the head is
               essentially linear to flow rate,  providing  that  free
               discharge exists.  Figures 4.1 and  4.2 illustrate  a Kennison
               nozzle  and the relationship between flow rate and  head.
                                    119

-------
                         C.
                         n
                         n>
to
o
                         •a
                                                     HEAD- INCHES
0 100 2OO 300 4OO 50O 6OO
FLOW- GALLONS PER MINUTE
>ical rating curve for a 10 in. Kennison nozz
3-MW*Oia>-J
-------
     The Kennison nozzle is designed to measure flow in partially
     filled pipes.  If high flow conditions fill the pipe/ the
     nozzle will overflow.   Any measurements taken daring this
     period will be inaccurate.

     For low flow and low head applications, the manufacturer has
     available a half section Kennison nozzle.

C.    Accuracy and Repeatability

     The accuracy of the Kennison nozzle is +_2% of actual flow
     when properly installed and operated between 10 and 100%
     capacity of the nozzle.  At flows of less than 10% of maximum
     flow accuracy will reduce to + 3 to +_5% of actual flow.

     The accuracy of any flow indicator is dependent on the
     combined accuracy of the nozzle (primary element) and the
     hydraulic level measuring device (secondary element).  An
     accuracy of +_5% of flow is considered reasonable when
     recording or indicating flow in the linear operating range of
     the nozzle.

     The manufacturer states that accuracies of _+0.1% can be
     attained if the nozzle is flow tested in a hydraulics
     laboratory.

D,    Manufactured Options

     The Kennison nozzle is a proprietary product of BIF, a unit
     of General Signal.  Available options include:

     1. .  A half section nozzle for measuring flow under low
          hydraulic head conditions, or lower than standard flow
          rates.

     2.   Cast iron or fiberglass material of construction.

     3.   Pressure tap connection on left or right side of nozzle.

     4.   Hydraulically operated vent cleaner for remotely or
          automatically initiated cleaning of the pressure tap.

     5.   Flow indicator.

     6.   Stilling well, level float, and transmitter with an
          output characterized for the nozzle.

     7.   Upstream spool piece and capacitance probe linearized to
          the nozzle.
                         121

-------
Installation

1.   Elevate the nozzle invert (bottom) above the level of
     the downstream surface to ensure free discharge
     conditions.

2.   Level the nozzle in the horizontal plane (lengthwise and
     crosswise).

3.   Install a thick gasket between the nozzle flange and
     pipe to facilitate leveling.

4.   Ensure a uniformly distributed non-turbulent flow by
     following the manufacturer's recommended approach
     conditions.  They are:

     a.   Eight pipe diameters of unobstructed straight pipe
          upstream of the nozzle.

     b.   Slope of the pipe line should not exceed the
          tabulated limits for the nozzle size selected as
          indicated in Table 4.2.

     c.   Line velocity should not exceed tabulated approach
          velocities for the nozzle size selected as
          indicated in Table 4,3.

5.   Set the invert of the nozzle flange and the mating pipe
     flange at the same elevation.

6.   Consult the manufacturer's engineering data bulletin for
     details on the installation of a secondary level
     measuring system.
 TABLE 4.2.  LIMITING SLOPE FOR APPROACH PIPING

Nozzle Size (In.)                  Slope (Meters Per Meter)

        6                      .        0.0070
        8                              0.0050
        10                             0.0040
        12                             0.0033
        16                             0.0027
        20                             0.0023
        24                             0,0021
        30                             0.0020
        36                             0.0020
                    122

-------
      TABLS 4.3.   MAXIMUM LINE VELOCITY FOR KENNISOM
                   :JOZ2L3 INSTALLATIONS

                                       Maximum Line Velocity
     Nozzle Size  (In. )                  	(m/sec)	

             6                              0.67
             3                              0.67
             10                  •           0.70
             12                •             0.79
             16                             0.91
             20                             1.00
             24                             1.13
             30                             1.13
             36                             1.13

P.   Designer Checklist

     Use the following checklist when designing or reviewing
     Kennison nozzle applications.  All items should be answered
     affirmative.

     1.   Have the manufacturer's rating curves been consulted to
          assure  the selected nozzle size meets the following
          criteria?

          a.   Has the smallest practical size been selected for
               the anticipated range of flows?

          Refer to the manufacturer's rating curves for the
          desired nozzle size.

          b.   Is the minimum anticipated flow greater than 10% of
               the nozzle capacity?

          c.   Will the pipe be less than full under maximum flow
               conditions?

     2.   Is the  invert of the nozzle above the downstream liquid
          level at all times?

     3.   Is the  straight pipe upstream of the nozzle greater than
          3 diameters?

     4.   Is slope of the pipe less than the manufacturer's limits?

     5.   Is approach velocity within the limits specified by the
          manufacturer?

G.   Acceptance and Performance Monitoring

     Install either a pressure gauge or manometer on the zero
     check tap.  Use readings from this indicator to pick the flow
     from the manufacturer's rating curve.

                         123

-------
     Other methods for flow verification and testing are described
     in Section 7.1.

H.   Maintenance and Calibration

     1.   Weekly:  Operate the vent cleaner to remove any buildup
          or obstruction in the pressure tap.

     2,   Weekly:  Measure the hydraulic head manually to
          determine if calibration of the secondary system is
          required.

     3.   Weekly:  Inspect the secondary level system and maintain
          as required.

     4.   Semiannually:   Check for buildup of solids and remove as
          required.

I.   Common Deficiencies

     Improper approach conditions constitute the most common
     problem in the use of the Kennison nozzle; either the slope
     of the approach piping is too great and/or the approach
     velocity is too high.

J.   References

     1.   BIF a unit of General Signal.  Kennison Open Flow
          Nozzle.  Engineering Data Sheet No. 135.21-1.  West
          Warwick, Rhode Island.

     2.   Grant, D.M.  Open Channel Flow Measurement Handbook.
          ISCO, Inc., Lincoln, Nebraska, Second Edition, 1981.
                         124

-------
4.2  PALMER-BOWLUS FLUME

     A.    Application
          Palmer-Bowlus flumes are normally installed in sewers between
          sections of pipe.  The following general conditions should
          apply when selecting a Palmer-Bowlus flume.

          1.    Open channel with round bottom or partially filled pipes
               (less than 90% filled)  where fabrication of a flow
               transition approach section to accommodate a parsnall
               flume is not practical.

          2.    Hydraulic head loss must be minimized.

          3.    Sediment or solids in the measured stream (velocities in
               the flume tend to flush away deposits).

          4.    variations in the flow rates are expected to be within a
               10 to 1 range.

          5.    The flow entering the flume is subcritical (velocity is
               less than in the flume throat), non-turbulent, and
               uniformly distributed.
       TABLE  4.4.   PALMER-BOWLUS FLUME APPLICATION GUIDELINES

      	Recommended	               Not Recommended
     Raw  sewage                          Sludges
                                        Chemicals
    B.    Principle of  Operation

          The  Palmer-Bowlus flume is a restriction in the channel which
          produces  critical flow through the throat of the flume.  This
          restriction also causes the water to bacKup upstream of the
          flume.  Figure 4.3 shows the sections of a Palmer-Bowlus
          flume.  The throat cross-section is trapezoidal.
                            125

-------

  TEXT
  HJJ-fc
                   	 figure 4.3.  Palmer-Bowlus £lume.
              Flow rate is related to upstream depth.   Thia relationship is
              derived analytically from  an  energy balance between the point
              of depth measurement and the  flume throat.  The point of
              depth measurement  is about 1/2  pipe diameter upstream from
              the entrance to the flume  (refer to Pigure 4.4).
uAir L!\E
Ur 7CX.T *
                                              126	_	
                                                       Reproduced from
                                                       best available copy.

-------
                                0/2 ,
                                         FLOW-
            \    A
                                           20 •*• 2
          Figure 4,4.  Free flow/depth relation.

     Palmer-Bowlus flumes are subject to free and submerged
     discharge conditions.  Free discharge will prevail as long as
     the ratio of downstream to measured depth  (H /H )  does not
     exceed 0.90.  One reference suggests that  the H /H  ratio
     should not exceed 0.85.  When the H /H  exceeds 0.90,
     submerged flow exists.  Correction factors are not available
     for submerged flow conditions.

     The Palmer-Bowlus flume size is determined by its
     cross-section diameter.  Prefabricated flume liners are
     available in sizes from 0,1 - 1.5 m (4-60  in).  To avoid
     selecting an oversized flume, care should be taken to base
     flume size on actual flow rather than nominal pipe.

     Two elements are required to measure flow with a
     Palmer-Bowlus flume.  The primary element  is the
     Palmer-Bowlus flume structure; the secondary element is a
     level measuring device.  For additional information on
     equipment to measure level, refer to Section 5.0 of this
     handbook.

C.   Accuracy and Repeatability

     When properly installed, the accuracy of the flume primary
     element is +.3% of full scale.  A given flow differential will
     produce a relatively small head differential thus requiring a
     sensitive, accurate level measurement for  best results.  In
     operation, the Palmer-Bowlus flume and a level measuring
     device should produce a combined accuracy  of _+10% of full
     scale.
                        127

-------
     There are additional sources of arror which can add  to  the
     inaccuracy of tne meter.  The principal ones ara:

     1.   Longitudinal slope of the flume floor greater tnan 1.5%.

     2.   Any transverse slope of the flume floor.

     3.   Approach conditions which do not produce a smooth  flow
          with uniform velocity distribution parallel  to  the
          center line of the flume.

     4.   Incorrect zero reference of the level measurement  device.

     5.   Where stilling wells are used  (see page  127) connector
          hole is improperly sized.

D.   Manufactured Options

     Palmer-Bowlus flumes typically are purchased as a
     prefabricated liner to be set in concrete or grouted into a
     half-section of pipe.  Some available options include:

     1.   Material of construction.

     2.   Alternative configurations:

          a.   Basic insert flume.

          b.   Flume with integral approach section.

          c.   Cutback flume for insertion into a manhole
               discharge pipe.

     3.   Flanged ends.

     4.   End bulkheads to fit in a larger pipe.

     5.   For flumes with integral approach sections:

          a.   Depth gauge flush mounted  in the sidewall.

          b.   Stilling well connection.

          c.   Attached stilling well.

          d.   Removable bubbler tube installed in the sidewall.
                  X
     6.   Nested  flumes.

          A large flume with a smaller one mounted internally.
          The smaller flume  is removed when flow  exceeds  its
          capacity.
                         128

-------
Installation

1.   Install the flume so that the floor of  the  flame  is
     level longitudinally and laterally.

2.   Establish the flume floor elevation to  prevent
     submergence conditions at maximum flow.

3.   Plan the flume installation to allow access  for
     inspection to ensure correct elevation  and  leveling of
     the floor.

4.   Use an approach channel long enough to  create a
     symmetrical, uniform velocity distribution  and a
     tranquil water surface at the flume entrance.  A  general
     rule is the greater of either 20 throat widths or 3 pipe
     diameters of straight run should exist  upstream of the
     flume inlet.

Designer Checklist

Use the following checklist when designing or  reviewing
Palmer-Bowlus flume applications.  All items should be
verified affirmative for correct application and installation.

1.   Has the smallest practical size Palmer-Bowlus flume been
     selected for the anticipated range of flows?

     a.   As a rule of thumb, the flume throat width  is
          one-third to one-half of the pipe  diameter.

     b.   Another sizing guide is that the maximum flow
          expected should fall within 70-100%  of the maximum
          capacity for the selected flume size (1, 3).

     c.   A minimum depth of 0.15 m  (0.5 in) should exist  at
          the minimum actual flow.

2.   Is the flume floor elevation sufficient to  avert
     submerged flow conditions?

3.   Does a straight channel longer than 20  throat widths  or
     8 pipe diameters exist upstream of the  flume?

4    Hill the anticipated upstream flow provide
     non-turbulent, wave-free approach conditions?

5.   Is the upstream approach velocity subcritical?

6.   Do any downstream obstructions exist which  could
     restrict the discharge of the flume?

7.   Is a reference gauge provided for measuring depth in  the
     flume?

                    129

-------
      3.    is  the  point  of  level measurement correctly located on
           the  flume?

      9.    Is  level  sensor  zero  referenced to the floor of flume at
           the  center  line  of  the throat?

      10.   If  required,  is  a  stilling  well provided for level
           measurement?

           The  following items pertain to  the stilling well:

           a.   Does the vertical height extend below and above the
               anticipated operating  depths in the flume?

           b.   Is the flume opening for the stilling well sized
               large enough to  avoid  sensor lags and plugging?

           c.   Has the  flume opening  for  the stilling well been
               correctly located on the length of the converging
               section  wall?

           d.   is the flume opening for the stilling well
               positioned  below  the operating  level at minimum
               flow?

           e.   Is a fresh  water  purge  piped into the stilling well?

G.   Acceptance and Performance  Monitoring

      It is recommended  that a depth gauge be mounted upstream of
      the flume entrance so that  manual readings and flow
     calculations can be made to check remote  flow indicators or
      recorders.

     Other methods for  flow verification  and testing are described
      in Section 7.1.

H.   Maintenance and Calibration

      1.   Palmer-Bowlus flume.

           a.   Weekly, check the depth gauge with other level flow
               indications for the flume  to determine if
               calibration of the secondary system is required.

          b.   Periodically, wipe down the  flume walls to remove
               slime or other buildup.

          c.   Check for bottom  deposits  and remove  as required.

          d.   Quarterly, check  the zero  of  the reference depth
               gauge.

          e.   Semiannually, examine the  flume  surfaces for  signs
               of deterioration  and wear.

                        130

-------
     2.   Stilling well (if used).

          a.   Periodically, check for solids accumulation and
               clean as necessary (establish the interval between
               checks by experience).

          b.   If purge water is used, check the flow rate daily
               and adjust as needed.

I.   Deficiencies

     The following problems are encountered in existing
     Palroer-Bowlus flume installations.

     1.   Plume sized too large or small for the operating flow
          range.

     2.   Insufficient straight channel upstream resulting in
          non-uniform velocity distribution through the throat.

     3.   Excessive transverse or longitudinal slope to the flume
          floor.

     4.   Measuring the depth of the hydraulic head at the wrong
          location.

     5.   Level sensor zero and the flume floor elevation not
        .  equal.

     6.   Using an incorrect equation for calculating flow from
          level.

     7.   No provisions for purging the stilling well when
          measuring a solids-bearing stream (buildup of deposits
          in the stilling well renders the level sensor
          inoperable).

     8.   The foundation of the flume is not water tight, allowing
          leakage under or around the flume.

J.   References

     1.   Grant, D.M.  Open Channel Flow Measurement Manual.
          ISCO, Inc., Lincoln, Nebraska, 1981, Second Edition.

     2.   Metcalf and Eddy, Inc.  Wastewater Engineering:
          Treatment/Disposal/Reuse.  McGraw-Hill, 1979.

     3.   Kulin, G.  Recommended practice For The Use of Parshall
          Flumes and Palmer-Bowlus Flumes in Wastewater Treatment
          Plants.  EPA-600/2-84-186.  Environmental Protection
          Agency, Cincinnati, Ohio, November, 1984.

     4.   Flow:  Its Measurement and Control in Science and
          Industry, Volume Two.  Instrument Society of America,
          1981.

                         131

-------
4.3  PARSHALL FLOMS

     A.    Applications
          Parshall flumes  are suitable for metering flow under the
          following general conditions:

          1.    Open channels.

          2.    Hydraulic head loss must be minimized.  Typically, head
               loss for a  Parshall flume head loss is approximately 25%
               of the head loss  for a weir of equal capacity.

          3.    Sediment or solids in the measured stream (velocities in
               the flume tend to scour and flush away deposits).

          4.    Anticipated flow rates will vary widely.  Depending on
               flume size  and the accuracy of leva! measurement, a
               "laximum to  minimum flow range of 20 to 1 is reported for
               Parshall flumes.

          5.    Approach conditions upstream of the flume will insure
               that the entering flow is tranquil and uniformly
               distributed.
         TABLE  4,5.  PA3SHALL FLUME APPLICATION GUIDELINES

     	Recommended	   	Not Recommended	

     Raw sewage                         Sludges
     Primary effluent                   Chemicals
     Secondary effluent
     Plant  final effluent
     Mixed  liquor


     B.   Principle of  Operation

          The Parshall  flume is a device for measuring liquid flow  in
          open channels.  The Parshall flume is a constriction of the
          channel that  develops a hydraulic head which is proportional
          to flow.  Figure 4.5 illustrates the shape and sections of a
          Par .snail flume.
                               132

-------
                 CONVERGING
                  SECTION
                                   DIVERGING
                                   SECTION
                 •WING
                  WALL
       FLOW
   Figure  4.5.   Parshall flume flow element.
Parshall flume sizes refer  to  the width of the throat
section.  Flumes are available in  sizes from 0.025 m (1 in)
up to 15 m  (50 ft).  Large  flumes  are constructed on site,
but smaller flumes can  be purchased as prefabricated
structures or as lightweight shells which are sst in
concrete.  Dimensions for the  fabrication of Parshall flumes
are contained in the Water  Measurement Manual published by
the United States Department of the Interior.

If a Parshall flume has been constructed to standard
dimensions and properly set, it is  possible to calculate flow
through the flume by measuring level at a single point.  The
location for the level  measurement  is shown as H  in Figure
4.6.  Flow  is approximately proportional to the three halves
power of the hydraulic  head.   Simplified equations can be
found in Reference 2.
                      133

-------
       FLOW
                  THROAT WIDTH
                Ha= HYDRAULIC HEAD
      Figure  4.6.   Head/width parameters.
Two flow conditions can exist in the Parshall  flume:   free
flow and submerged flow.  Free  flow exists  when  the  only
restriction is the throat width and the water  is not slowed
by downstream conditions.  If the  flow through the  flume
increases sufficiently, this will  cause a rising downstream
channel level which will impede the discharge  from  the flume,
thereby slowing the fluid velocity.  This is known  as
submerged flow.

It might be expected that the flume discharge  would be
reduced as soon as the tailwater level exceeds the  elevation
of the crest.  Tests have shown that this is not the case.
Free flow conditions can still exist even with some degree of
submergence.  Figure 4.7 shows  the head relationship for free
flow.  Table 4.6 lists flume sizes and the  limits of free
flow submergence.  For free flow conditions, the depth
measurement (H ) can be used to calculate the  flume discharge
flow.
                 •<5O-ao%
       Figure 4.7.  Free flow submergence.
                      134

-------
              TABLE 4.6,  SUBMERGENCE LIMITS

Flume Size                                      % Submergence

0.025, 0.05, 0.075 m (1, 2, 3 in)                     50
0.15, 0.23 m (6, 9 in)                                 60
0.3 - 2.4 m (1-8 ft)                                  70
3 - 15 m (10-50 ft)                                   80
     Although Parshall flumes can operate with a submergence
     greater tnan those shown in Table 4.6, a second level
     measurement and a correction factor is required to calculate
     flow.  There is a loss of accuracy at submergence, and it is
     not a recommended design.

     Two elements are involved in obtaining a flow measurement
     with a Parshall flume.  The primary element is the Parshall
     flume structure and the secondary element is the level
     measuring device.  For additional information on methods to
     measure level refer to Section 5.0 of this handbook.

C.   Accuracy and Repeatability

     The accuracy of a measurement derived using a Parshall flume
     depends on the combination of the accuracies of the primary
     (flume) and secondary (level measurement) elements.  For a
     correctly fabricated and installed flume the estimated
     accuracy of the depth discharge equation is ^_3% of flow.  A
     combined flume and level measurement accuracy of +_5% of flow
     is attainable with repeatability to _+l/2% of flow.

     Additional sources of error, if uncorrected, can decrease the
     accuracy of the flow measurement.  These include:

     1.   Deviations of the throat width from standard dimensions.

     2.   Longitudinal slope of the floor in the converging
          section.  Tests on a 0.75 m (3 in) flume demonstrated
          that a downward sloping floor produced added errors of 3
          to 10% from low to high flow conditions.

     3.   Transverse slope of the flume floor.

     4.   Approach conditions which do not produce a smooth flow
          with uniform velocity distribution parallel to the
          center line of the flume.

     5.   Incorrect zero reference of the level measurement device
          to the center line elevation of the crest.

     6.   If a stilling well is used, the connector hole is
          improperly sized.

     7,   Incorrect zero reference of the level measurement device.

                          135

-------
D.   Manufactured Options

     Although Parshall flumes can be constructed on site, most
     flumes used in wastewater applications are prefabricated
     structures or liners for setting in concrete.  Some available
     options include:

     1.   Material of  construction.

     2.   Stilling well connection.

     3.   Attached stilling well.

     4.   Depth gauge  integrally mounted in the converging section
          sidewall.

     5.   A cavity for a characterized capacitance level measuring
          probe molded into the flume sidewall.

     6.   Removable bubbler tube installed in the sidewall.

     7,   A large flume with a smaller one mounted internally.
          The smaller  flume is removed when flow exceeds its
          capacity.

E.   Installation

     1.   Construct or install the flume so that the floor section
          is level longitudinally and transversely.

     2.   Establish the flume floor's elevation to prevent
          submergence  conditions at maximum flow.

     3.   Plan the flume installation to allow access for
          inspection of the flume to ensure correct elevation and
          leveling of  the floor.

     4.   Provide an approach channel long enough to create a
          symmetrical, uniform velocity distribution and a
          tranquil water surface at the flume entrance.  A general
          rule is that 10 channel widths of straight run should
          exist upstream of the flume inlet.

P.   Designer Checklist

     Ose the following checklist when designing or reviewing
     Parshall flume applications.  All items should be verified
     affirmative for a correct application and installation.

     1.   Has the smallest practical Parshall  flume been selected
          for the anticipated range of flows?

          a.   As a guide, the maximum flow expected should fall
               within 70-100% of the maximum capacity for  the
               selected flume size  (1, 3).

                          136

-------
          b.   A depth of at least 0.15 m (0.5 in) should exist at
               the minimum actual flow,

     2.   Is the flume floor elevation high enough (relative to
         'downstream conditions) to prevent submerged flow?

     3.   Does a sufficient straight run of pipe or channel exist
          upstream?

     4.   Will the upstream flow be non-turbulent and wave free?

     5.   Do any downstream obstructions exist which could cause a
          restriction to the discharge of the flume?

     6.   Is a depth gauge included for calibrating the flume?

     7.   Is the level sensor correctly located-on the flume?

     8.   Is the level sensor zero correctly referenced?

     9.   If required for the application, is a stilling well
          provided?.

     10.  The following items pertain to the stilling well:

          a.   Is the vertical height extended below and above the
               anticipated operating depths in the flume?

          b.   Is the flume opening for the stilling well sized
               large enough to avoid sensor lags and plugging?

          c.   Has the flume opening been correctly located on the
               length of the converging section wall?

          d.   Is the flume opening positioned below the lowest
               flow operating level?

          e.   If the flume is used to measure raw sewage or mixed
               liquor flow, has a water purge been piped to the
               stilling well?

G.   Acceptance and Performance Monitoring

     A depth gauge mounted on the converging section is
     recommended so manual readings and flow calculations can be
     made to check remote flow indicators or recorders.

     Other methods for flow verification and testing are described
     in Section 7.1.
                          137

-------
H.    Maintenance and Calibration

     1.    Parshall flume.

          a.   Weekly, check the depth gauge with other level flew
               indications for the flume to determine if
               calibration of the secondary system is required.

          b.   Periodically, wipe down the flume walls to remove
               slime or other buildup.

          c.   Check for bottom deposits and remove as required.

          d.   Quarterly,  check the zero of the reference depth
               gauge.

          e.   Semiannually, examine the flume surfaces for signs
               of deterioration and wear.

     2.    Stilling well (if used).

          a.   Periodically, check for solids accumulation and
               clean as necessary (establish the interval between
               checks by experience).

          b.   If a water purge is used, check it daily and adjust
               the flow rate as needed.

I.   Deficiencies

     The following problems are encountered in existing Parshall
     flume  installations.

     1.   Insufficient straight channel upstream, resulting in
          non-uniform velocity distribution through  the throat.

     2.   Sloping floor in the converging section.

     3.   Low flume floor elevation  (relative to downstream
          channel level) resulting in submerged flow condition.

     4.   Measuring the depth of  the hydraulic head  at the wrong
          location.

     5.   Using an incorrect equation for calculating flow from
          level.

     6.   No provisions for purging the stilling well when
          measuring a solids-bearing  stream  (buildup of deposits
          in the  stilling well  renders  the level sensor
          inoperable).
                           138

-------
     7.   The foundation is not water tight, allowing leakage
          under or around the flume.

     8.   Flume sized too large for the operating flow range.

J.   References

     1.   Grant, D. M.  Open Channel Plow Measurement Handbook.
          ISCO, Inc., Lincoln, Nebraska, 1981, Second Sdition.

     2,   Liptak, 3. G.  and K. Venczel.  Instrument Engineers
          Handbook of Process Measurement.  Chilton Book Company,
          Radnor, Pennsylvania, 1969, Revised, 1982.

     3.   Water Measurement Manual.  U.S. Department of the
          Interior, Bureau of Reclamation, U.S. Government
          Printing Office, 1981, Second Edition."

     4.   Kulin, G.  Recommended Practice For The Use of Parshall
          Flumes and Palmer-Bowlus Flumes In Wastewater Treatment
          Plants.  EPA-600/2-84-186.  Environmental Protection
          Agency, Cincinnati, Ohio, November, 1984.

     5,   Instrumentation In Wastewater Treatment Plants.  Manual
          of Practice No. 21, Water Pollution Control Federation,
          1978.
                          139

-------
4.4  WEIR

     A.    Application
          A weir  is used to measure flow in open channels where the
          water is free of suspended solids.   Consider the following
          general conditions when selecting a weir for the primary flow
          element.

          1.   Water quality should be equal  to secondary effluent or
               better.

          2.   Sufficient hydraulic head exists so a weir can be used.
               Typically, the head loss of a  rectangular weir is four
               times that of a Parshall flume of equal size at the same
               flow.

          3.   Flow rates vary over a large range.  A range of flows of
               20 to 1  can be tolerated by most weirs.  For weirs
               larger than 2.5 m (8 ft), rarges of 75 to 1 are
               reported.  These wide ranges are not recommended.

          4,   The approach conditions insure that at all flow rates
               the flow is tranquil, free of eddies or surface
               disturbance.  Under maximum flow, approach velocities in
               the upstream channel should not exceed 10 cm/s (4 in/s).
  TABLE 4.7.  WASTEWATER TREATMENT FACILITY APPLICATION GUIDELINES

     	       Recommended                     Not Recommended
     Secondary Effluent                 Raw Sewage
     Primary Effluent (with             Mixed Liquor
       provisions for sluicing)         Sludge

     B.   Principle of Operation

          A weir is a dam or bulkhead placed across an open channel
          with an opening on the top through which the measured liquid
          flows.  The opening is called the weir notch; its bottom edge
          is called the crest.  Normally the notch is cut from a metal
          plate and attached to the upstream side of the bulkhead.
          This is done to prevent the water from contacting the
          bulkhead and is known as a sharp-chested weir.  See
          Figure 4.8.  Weirs without a plate where the water contacts
          the bulkhead are known as a broad-crested weir.  This
          presentation concentrates on sharp-crested weirs.
                               140

-------
	CRESTS
          WEIR
          PLATE
                                   RELIEVE TO
                                   ASSURE FREE FALL
                                        NAPPE
                                     BULKHEAD
        Figure 4.8.  Sharp-crested weir.

The water depth measured at a prescribed  distance  upstream
can be used to determine the discharge through the weir.
Characteristic head versus flow relationships are  governed by
the weir geometry.  All level measurements  are made  relative
to the crest elevation.

The weir openings are normally fabricated in rectangular,
trapezoidal, or V-notch shapes.  A trapezoidal weir  with a
side slope of 4:1 is known as a Cipolletti  weir.   Figure 4.9
illustrates the weir shapes.  Flow as a function of  upstream
head (h) is expressed by empirical equations.  See Figure
4.8.  General equations for each weir shape are given below.
These are covered in more detail in the technical  references
(1, 2).
                     141

-------
                               END
                          CONTRACTIONS
^.
CREST -v
•*>:
             RECTANGULAR
(C1POLLETTI) TRAPEZOIDAL
                             END
                            -CONTRACTION
                                                 9- 60* OR 90*
                                                   TYPICALLY
                                V-NOTCH



                     Figure 4.9.  Weir shapes.

The following equations show the relationship between flow and the
measured head.

For a rectangular weir:

     Q = K(L-0.2H)H3/2

For a Cippoletti weir:

      Q- KLHV2

For a V-notch weir:

     Q = K tan 1/2 -6- H&/2

Where:

     Q » Rate of flow.
     L » Crest length.
     H » Head of flowing liquid.
     -*• » V-notch angle in degrees.
     K » Constant dependent the units of flow.
                               142

-------
    A special rectangular weir without end contractions  can be
    installed with the sidewalls of the channel forming  the ends
    of  the weir.  This is known as a suppressed weir  and is shown
    in  Figure 4. 10.  When this type weir is applied,  an  air vent
    must  be installed to allow free access of air beneath the
    nappe for free flow.
             AIR
            VENT
        Figure 4.10.  Suppressed rectangular weir.
     V-notch weirs  are  suitable for flows up to 17 kl/m (4500
     gpm).  Rectangular and Cipolletti weirs are capable of
     measuring much higher flows than the V-notch wier.

C.   Accuracy and Repeatability

     Accuracy of .+2% for the head versus flow relationship is
     attainable.  However, the weir is a primary element, and the
     accuracy of flow indicated or recorded flow is also dependent
     on the secondary elements; i.e., level sensor and flow
     converter. Therefore, for a properly installed weir and
     level sensing  secondary, it is reasonable to expect a _+_5%
     flow measurement accuracy.  Refer to Instrumentation Part 7.0
     for more information on selecting and installing level
     transmitters.

     To obtain the  best accuracy possible when designing and
     installing a weir, observe the following factors:

     1.   The minimum head (see Figure 4.8) should be 6 cm (2.5
          in) or greater.

     2.   The maximum head is less than one-half the height of the
          weir.

     3.   When using rectangular or Cipolletti weirs, the maximum
          head is less  than one-half the crest length of the weir.

                         143

-------
4.    Rectangular and Cipolletti weir crests snould be level.

5.    Use a V-notch weir for low-flow measurement.

6.    All edges and corners of the weir must oe sharp.

7.    Weir edges should be straight,  smooth, and free of burrs.
                                     i

8.    The approach channel should be  straight and of uniform
     cross-section for a length equal to at least  fifteen
     times the maximum head on the weir.

9.    The channel should have a free  fall of 15 cm  (6 in)
     downstream of the weir.

Manufactured Options

The weir is normally fabricated for  each installation.
Nonetheless, it may be desirable to  consider some  optional
features when fabricating a weir such as:

1.    Level sensor stilling well,

2,    Depth gauge referenced to the crest elevation, and

3.    A sluicing slit with cover located at the bottom of the
     bulkhead for flushing out solids that may collect behind
     the weir.

Installation

1,   Make the upstream face of the bulkhead and weir plate
     smooth, and install it in a vertical plane perpendicular
     to the axis of the channel.

2.   Insure the crest is level for  rectangular and Cipolletti
     weirs.  For a V-notch weir, insure the bisecting line of
     the V is vertical.

3.   Cut the V-notch weir angle precisely and mount the plate
     so the angle is bisected by a  vertical line.

4.   Machine or file the weir edges  to be straight and free
     of burrs.  Chamfer the trailing edge to obtain a crest
     thickness of 1-2 mm (0.03 - 0.08 in).

5,   Install the weir so the distance from the weir crest to
     the bottom of the approach channel is the greater of 30
     cm (12 in) or two times the maximum head.

6.   Design the weir so the end contractions on each side
     (except suppressed weirs) will be a minimum of 30 cm (12
     in) or two times the maximum head.

                     144

-------
     7,    Provide air  vents  under  the nappe  on both  sides of a
          suppressed rectangular weir.

     8.    Rectangular  weir sides must be  straight  up and down.

     9.    Slope  the side  of  a  Cipolletti  weir  outward 1 horizontal
          to 4 vertical.

     10.   Make the crest  length of  rectangular and Cipolletti
          weirs  at least  three times  the  maximum upstream head.

     11.   Construct the bulkhead opening  approximately 3 cm  (3 in)
          larger on all sides  than  the weir  notch.

     12.   Slope  the top of the bulkhead down to assure that  the
          nappe  falls  free without  hitting the bulkhead.

     13.   Locate the level sensor  next to the sidewall so it can
          be easily reached,

     14.   Position the level sensor upstream of the  weir at  least
          four  times  the  maximum  head to  avoid the effect of the
          drawdown.

     15.   Install the  depth  gauge and level sensor so the zero
          reference  elevation is  the same as the weir crest
          elevation.

F,   Designer Checklist

     Consider the following  when  designing or reviewing weir
     applications. All  checklist questions should be answered
     "yes."

     1.    Is the level sensor located upstream at least four times
          the maximum  weir  head?

     2.    Is the maximum downstream liquid level at least 6   on
          (2.5 in) below the elevation of the crest?

     3.    Is the cross-sectional  area of  the approach channel at
          least eight  times the cross section of  the water
          overflowing  the crest at maximum flow?

     4.    Is the approach channel straight and of uniform cross
          section for  a length at least fifteen times the maximum
          head?

     5.    If a suppressed rectangular weir is being used, has an
          air vent been provided under the nappe  on both sides of
          the channel?

     6.    At minimum flow,  does the head above the crest exceed
          6 cm  (2.5 in)?

                          145

-------
     7.   Is the weir notch sized and shaped so the nappe will
          clear the bulkhead and fall free?

     8.   Is the length of the bulkhead end contractions on each
          side of the weir opening at least two times the maximum
          head above the crest or 30 cm (12 in), whichever is
          larger?

     9.   Is the height of the weir crest above the channel bottom
          greater than twice the maximum head or 30 cm (12 in),
          whichever is larger?

     10,   Is the length of the rectangular or Cippoletti wei~
          crest at least three times the-maximum head?

     11.   Is the maximum velocity in che approach channel less
          than 10 cm/s (4 in/s)?

     12,   Is a depth gauge installed so periodic checks can be
          made on the level sensor?

G.   Acceptance and Performance Monitoring

     A depth gauge mounted adjacent to the level sensor is
     recommended.  Make periodic level readings and determine the
     flow by calculation or from a lookup table.  Compare remote
     flow readings with the value determined from the visual
     inspection as a conformance check on the calibration of the
     level sensor and flow converter.

     Other methods for flow verification and testing are described
     in Section 7.1.

H.   Maintenance and Calibration

     1.   Weekly check:

          a.   The level sensor with other level or flow
               indicators to determine if calibration of the
               secondary system is required.

          b.   Accumulation of bottom deposits and remove as
               required.

          c.   Stilling well (if used) for solids accumulation and
               clean as necessary.

     2.   Annual check:

          a.   Crest level,

          b.   Reference to zero on the depth gauge,

                          146

-------
          c.   Flush fitting of the weir plate to the bulkhead,

          d.   Leaks around the wier,

          e.   Weir notch for nicks, dents, and rounding of
               upstream corners.

I.    Deficiencies

     The following problems have been encountered in existing weir
     installation.

     1.   Insufficient head during low flow conditions so there is
          no free air space under the nappe-

     2.   Suppressed rectangular weirs without air vents under the
          nappe.

     3.   Insufficient relief on the bulkhead so the nappe strikes
          the bulkhead interfering with the free fall.

     4.   Pool level downstream is too high so insufficient free
          fall exists.

     5.   Weir notches cut from metal plate stock and installed
          without the edges finished to proper thicknesses, shape,
          or straightness.

     6.   Rectangular or Cipolletti weirs  installed without
          leveling the crest.

     7.   V-notch weirs with incorrectly cut angles.

     8.   Level sensor located too close to the weir.

     9,   Level sensors or gauges not zero referenced to the
          bottom of the weir notch.

J.    References

     1.   Water Measurement Manual.  U.S.  Department of the
          Interior, Bureau of Reclamation, U.S. Government
          Printing Office, 1981, Second Edition.

     2.   Grant, D. M.  Open Channel Flow  Measurement Handbook.
          ISCO, Inc., Lincoln, NebrasKa, 1981.
                          147

-------
5.0  LEVEL MEASUREMENT


     5.1  BUBBLER LEVEL MEASUREMENT

          A.   Applications
               Bubbler level measurement instruments are used throughout
               the wastewater treatment process for measuring both liquid
               level and differential liquid level.

               Bubblers are frequently used to sense the hydraulic head
               created by flumes and weirs in open-channel flow
               measurement.  A special signal converter indicates  flow
               based on the level sensed by a bubbler.  This section  of
               the manual addresses the use of bubblers in open  tanks
               which is applicable to open-channel  flow measurement.
        TABLE 5.1.   BUBBLER LEVEL MEASUREMENT APPLICATION GUIDELINES
          Recommended                  Not Recommended

          Liquid treatment processes   Digesters
                                       Volatile chemical storage  tanks
          B.   Principle of Operation

               An open-ended pipe, called  the bubbler  tube  or  dip  tube,
               is connected to  an air supply and  positioned in the
               process so  that  the open  end is set at  a  reference  level.
               A constant  air rate-of-flow regulator  is  used  to  maintain
               air  in the  tube  with enough excess to  continually bubble
               out  the open end.  Thus,  the air pressure in the  pipe is
               equal  to the head of the  process liquid above  the
               reference level.

               A pressure  transmitter connected to the bubbler tube
               measures  the pressure of  the dip tube.  For  water,  the
               level  is equal to the pressure sensed  by  the transmitter.
               For  measuring other liquids, the transmitter must be
               calibrated  for that liquid's specific  gravity.   For closed
               tanks, a differential pressure transmitter is  used, with
               the  high-pressure port connected to the bubbler tube and
               the  low-pressure port connected to the gas space in the
               top  of the  tank. A schematic of the bubbler application
               is  shown  in Figure 5.1.
                                     148

-------
  LOW
PRESSURE
  AIR
 PURGE
 AIR
PURGE
                 OPEN TANK OR
               OP. CH. FLOW ELEMENT
          CLOSED TANK
                AIR
               PURGE
                                       BAR SCREEN
                      DIFFERENTIAL LEVEL
  Figure 5.1.   Typical bubbler applications.
Because of head loss  caused  by air flow in the tube and
connecting pipe, pressure at the transmitter will not be
exactly the same as at  the open end of the bubbler tube.
This difference in pressure  necessitates minimizing pipe
and fittings between  the rate-of-flow air regulator and
the dip tube.

Airflow head is affected by  bubble formation.  To minimize
errors, the bottom of the tube usually has a notch or an
angular cut to produce  a continuous stream of small
equally sized bubbles.  Buildup of process solids on the
end of the tube will  alter bubble formation; therefore,
the tube end must be  kept clean.
                     149

-------
     The air  supply rate  is  controlled  by a  pressure regulator
     and a flow control valve.   Typical airflow rates are 8-30
     cc/s (1-4 cfh).  Use a purge-rotameter to adjust the airflow.
     The air supply can be from instrument air, plant air,
     compressed gas tanks, or dedicated bubbler compressor.
     For applications requiring infrequent level readings, a
     hand-operated pump can be used.

C,    Accuracy

     The accuracy  of a  level  measured by a bubbler  system is
     dependent on  the uncertainty of the pressure measuring
     device  (see Section  6.2), process  fluid specific gravity,
     head loss in  the bubbler system, barometric pressure, and
     the temperature of both  the process fluid and  the bubbler
     system air.  Whrle errors of less  than  +0.1%  can be
     achieved, ac<~.racy is typically _+Q.5-l% of full scale.

0.    Repeatability

     Repeatability is dependent  on variances from standard
     conditions of any of the uncertainties  listed  above in
     paragraph C.

E.    Manufacturer's Options

     1.   Automatic purge cycle.

          A separate timer and valve control package for
          periodic cleaning of the bubbler tube-  A high
          pressure air purge removes buildup of material at the
          end of the tube when the pressure measuring device is
          momentarily isolated from the system and  full air
          supply pressure is applied to the  bubbler tube at
          periodic intervals from 8 to 24 hours.

     2.   Air supply.

          Bubbler systems can be furnished with a dedicated air
          supply consisting of:

          a.   A compressor, or where extra reliability is
               required, two compressors with automatic
               failover.  Intermittent duty compressors,
               capable of producing the high pressure purge
               required, range from 180 W (1/4 hp)-370 W  (1/2
               hp).  Adequate purge pressure for most
               wastewater applications  is about 500  kPa  (60
               psig).
                          150

-------
          b.   An air dryer.

          c.   An air filter.

          d.   A pressure tank with a capacity of about Q
               (2 gal.).

     3.    Enclosure.

          a.   NEMA 1,  general purpose.

          b.   NEMA 4,  watertight.

     4.    Purge gases.

          Where the oxygen contained in  an air supply system is
          objectionable,  nitrogen or another inert gas may be
          substitute^.   For explosive, volatile,  or hazardous
          atmospheres complete intrinsic safety can be achieved
          by using a pneumatic pressure  signal for remote
          indication.

     5.    Weatherization.

          Usually a thermostatically controlled heater.

     6.    Alarms.

          Available alarms include  low air flow,  low air supply
          pressure, purge-in-progress, and compressor failure.

P.    Installation

     The bubbler tube should  be rigidly  supported at a
     convenient location  in the tank.  The opening of the tube
     is  the lowest level  that can be detected, so set the tube
     depth at or below the lowest level  at which  a measurement
     is  needed.  Notch  the tube opening  to produce a continuous
     flow of small bubbles.

     Fabricate the bubbler tube from 1.25 cm (1/2 in.) diameter
     stainless steel  tubing o^ galvanized pipe.   Properly
     supported, this  makes a  rigid  installation which can
     withstand turbulence and wave  action.  A tee with one
     branch plugged,  when installed on top of the bubbler tube,
     provides an opening  for  a cleaning  rod when  the high
     pressure air purge cannot remove bubbler tip restrictions.
                         151

-------
 The bottom of the tube should be at least 8 cm (3 in.)
 from the cank bottom to avoid solids buildup on the tank
 floor.   This  offset must be included in the zero reference
 level  for the liquid in the tank.  An exception to this is
 a bubbler installed in a flume or ahead of a weir.  In
 flume  applications the bubbler tip must be at the same
 elevation as  the  flume floor or if elevated/ the degree of
 elevation must be compensated for in the flow
 calculation.   In  weir applications the bubbler tip must be
 at the same elevaf'on as the bottom of the notch, or if
 below  the notch,  the degree of offset must be compensated
 for in the flow calculation.

 To minimize level measurement errors caused.by air flow
 head loss, the air flow controller must be mounted as
 close  to the  dip  tube as possible and connected with a
 minimum of fittings an^. tubing.  For 1 cm (1/4 in.)
 tubing, the distanc«=> from the air purge regulator to the
 bubbler tube  should not exceed 15 m (50 ft).

 To ensure that the air purge tubing is free from traps
 where  moisture condensate can collect, install the tubing
 with a continuous downward slope from the pressure
 transmitter and the air flow controller to the bubbler
 tube.

 In open-tanks and flumes, for periodic reference checks
 and to facilitate recalibration if the tube is removed for
 cleaning or replacement, install a depth (staff) gauge in
 the tank at a location visible from the dip tube.  Zero on
 this gauge must correspond to the bubbler tube's zero
 reference.

 A typical installation schematic is shown in Figure 5.2.
 Maintenance access is needed for the clean-out tee and for
 the bubbler system enclosure.  Installation of the
 differential  pressure transmitter is addressed in Section
 6.2.

                                 TRANSMITTER    /LENGTH LESS
                                               THAN ISM (SOFT)
                                                    CLEANOUT
                                                      PLUG
INSTRUMENT
AIR SUPPLY
  Figure  5.2.   Open  tank  bubbler  installation.

                      152

-------
G.   Designer Checklist

     Ask the following questions when designing or reviewing
     bubbler level meter applications.  All checklist questions
     should be answered "yes."

     1.   Can air be passed through the process fluid?  If not,
          can another gas, such as nitrogen, be substituted for
          air?

     2.   Is the tank open or vented?  If not, is accumulation
          of air acceptable?

     3.   Are head losses from the air flow regulator to the
          bubble tube minimized?

     4.   Is the purge line length from the air flow regulator
          to the bubbler tube less than 15 m (50 ft)?

     5.   For process streams containing more than about 100
          mg/1 suspended solids,  is automatic purging included?

     6.   Does the air supply reliability match the need for
          level measurement reliability?

     7.   Is the bubbler tube mounted securely?

     8.   Is the clean-out tee accessible?

     9.   Is the bubbler enclosure suitable for its environment?

     10.  For open tanks, does the pressure transmitter
          reference  the same gas  space?  For example, a bubbler
          tube mounted outside and a  transmitter mounted inside
          a building will be exposed  to different atmospheric
          conditions.  Can this difference be tolerated?

H.   Maintenance and Calibration

     Maintaining and calibrating  the  differential pressure
     transmitter is  presented in  Section 6.2.

          Task               Frequency

     1.  Check Air flow.     Daily, or if the unit has a
                             low-flow
                             alarm detector, only at
                             calibration.
                          153

-------
     2.   Clean  tube.          Weekly  purge  foe  solids-bearing
                             fluids.   Manual cleanout  at
                             calibration.   Manual  cleanout when
                             tube  is  depressurized and fluid
                             enters.

     3.   Check  air  filter.    Weekly.   If the unit  has  a
                             low-flow alarm detector,  then
                             check filter  only at  calibration.

     4.   Calibrate.           Every two months,

     5.   Inspect              Depends  on type and .size  of
         compressor.          compressor.   Follow  the
                             manufacturer's recommendation.

I.    Deficiencies

     The following  problems  are commonly reported  for  bubbler
     systems.

     1.    Compressor  failure, and  measurement  loss,

     2.    Tube bubbler  opening does  not stay clean because no
          purge or  cleanout  is available.

     3.    Condensate  collection trapped in the purge  tubing.

     4.    Purge tubing  lines too long or  too small, creating
          excessive head losses.

     5.    The bubbler tube tip does  not correspond with the
          desired zero  level reference.

J.    References

     1.    Liptak,  B.  G, and K. Venczel.  Instrument Engineers
          Handbook.  Chilton Book Company, Radnor,
          Pennsylvania, 1969, Revised, 1982.

     2.    American Petroleum Institute.  Manual On Installation
          of Refinery Instruments and Control Systems, Part  I,
          Section 6 - Level.  Washington,  DC, 1974, Third
          Edition.
                          154

-------
5.2  CAPACITANCE PROES

     A.    Applications
          Capacitance probes are used to measure liquid levels throughout
          wastewater treatment plants.  For tiiis discussion, two kinds of
          probes are identified:  capacitance and capacitance with
          compensation for coating.  The compensated capacitance probes
          nave additional electronics to offset material buildup on the
          probe.

          Special probes are available that produce a signal proportional
          to flow in open channel flumes and weirs.  These probes are
          characterized to match the head/flow relationship of an open
          channel primary element.  Characterization is accomplished
          either of two ways:   one, by electronic calculation, or two, by
          variation of probe insulation thickness in a manner that
          produces a direct, linear relationship between capacitance and
          flow.  Consult with  manufacturers on special capacitance probes
          for direct flow measurement.
            TABLE 5.2.  UNCOMPENSATED CAPACITANCE PROBES
         WASTEWATER TREATMENT FACILITY APPLICATION GUIDELINES
     Recommended                  Not Recommended

     Potable  water                 Primary treatment
     Non-coating chemicals         Secondary treatment
     Tertiary effluent            Tertiary treatment
                                  Solids  handling
                                  Polymer solutions
                                  Lime slurry
              TABLE  5.3.  COMPENSATED  CAPACITANCE  PROBES
         WASTEWATER TREATMENT FACILITY APPLICATION GUIDELINE

    Recommended                  Not  Recommended

    Most  aqueous  solutions       Liquids where  heavy  grease  buildup
    Raw sewage                   could occur
    Secondary effluent
         Capacitance probes can also be used  to measure  the  level  of  dry
         material.  However, this discussion  deals with  only wastewater
         treatment solution applications.
                             155

-------
B.   Principle of Operation

     A capacitor can be described as two electrically conductive
     plates separated by a nonconductive material.  A probe  is
     usually constructed to form one plate of a capacitor.   The
     other plate is the tank wall or the measured  solution.  Between
     the probe and the tank wall is an air space above  the liquid
     surface and water below.  As the water level  rises,  the
     effective capacitance of the system increases.  This
     capacitance is linearly proportional to level and  is measured
     by a bridge circuit powered by a high frequency, 0.5-1.5 MHz,
     oscillator.  High frequency can reduce errors due  to shorting
     of the capacitor by conductive coatings.  Sometimes  capacitance
     probes are referred to as radio frequency  (RF) probes because
     of this measurement technique.

     Water in treatment processes is a good conductor.  For  this
     reason, the probe must be insulated.  The insulation's  exterior
     surface effectively becomes a third plate which complicates  the
     theory of operation.  Figure 5.3 shows one way of  illustrating
     the system in electrical terms.

     The situation becomes more complex if a conductive coating of
     process solids accumulates on the probe.  Through  a  combination
     of capacitance and conductance effects in the coating,  the
     probe fails to respond to changes in level below the top of  the
     coating.  The system's effective capacity remains  constant
     below this point.  Thus, for most applications in  wastewater
     treatment some method of compensating for coatings is essential.

     One method is based on assuming that the coating's capacitive
     reactance is equal to its resistive reactance.  The  coating's
     resistance is further assumed to be the greatest resistance  in
     an aqueous system.  This resistance is measured and  subtracted
     from the effective capacitance.  The result is proportional  to
     liquid level, although inaccuracies are introduced depending on
     how well the system matches the assumptions made.

     The probe is usually a cylindrical rod or cable inserted
     perpendicular to the water surface, as illustrated in Figure
     5.4.

     Probes are available for use in open channel  head  loss  type
     flow meters.  These probes are flat and shaped to  provide a
     signal proportional to flow.  In either style probe, accuracy
     decreases near the bottom because the submerged portion becomes
     less and less line the ideal capacitor with plates of infinite
     length.

C.   Accuracy and Repeatability

     For a clean probe, an accuracy of ±1% can be expected.  Where
     the probe becomes coated, accuracy will degrade to
     approximately ±5%.

                         156

-------
D.   Manufacturer's Options

     1.   probe type:

          a.   Rods of any length up to 5 m  (20 feet),

          b.   Cables of any length up to about 50 m  (150  feet)  with
               weight or anchor  to Keep probe  in  place,

          c.   Plat probes for open channel  flow  meters,  and

          d.   Proximity plate for non-contact with process  fluids.

     2.   Transmitter enclosure:

          a.   NEMA 3 - weatherproof, or

          D.   NEMA 4 - watertight.

     3.   Indicating meter.

     4.   Output:

          a.   4-20 mAdc, or

          b.   10-50 mAdc.

     5.   Probe materials:

          a.   304 stainless steel,

          b.   316 stainless steel,

          c.   Teflon insulator,

          d.   polyvinylidene  fluoride  insulator, or

          e.   PolyvinyIchoride  insulator.

     6.   Grounding rods.

     7.   Concentric probe.  Required for  non-conductive liquids and
          for  some installations  to provide  grounding or shielding
          from process liquid  turbulence.

     8.   Radio.frequency interference protection.
                         157

-------
          STAINLESS STEEL ROD OR CABLE




     PROBE INSULLAT1ON-
                         H
                         H
Figure 5.3.   Illustration of probe/tank capacitive relationship.
                              158

-------
 FLEXIBLE -x
  PROBE
(ANCHORED)
                                  -PROBE HEAD
STRAIGHT
 PROBE
                  FLEXIBLE
                   PROSE
                 (WEIGHTED)
          Figure  5,4.   Capacitance level sensor.
                           159

-------
E.   Installation

     1.   Install the probe as follows:
                                                                     t
          a.   Isolate from vibration and possible physical damage.

          b.   Do not mount in the direct stream of process flow.
               If necessary, install baffles or stilling well.

          c.   Mount vertically.

          d.   Mount at least 15 cm (6 in) from tan* wall to lessen
               chances of material buildup.

          e.   Mount so that probe can readily be removed for
               cleaning, inspection, or calibration.

     2.   Most manufacturers require the  transmitter be within
          75 m  (250  ft) of  the probe.  The cable must b«  furnished
          by the capacitance probe manufacturer and snould not be
          shortened  in  the  field without  consulting the manufac-
          turer.  Mount -the transmitter close  enough to the
          probe to see  indicator change as level changes  to allow
          one person to calibrate the  system.  If the transmitter
          is mounted further than this, provide a junction box
          near tha probe.   Allow enough cable  between the junction
          bc:c and probe for removing the  probe.  Provide  storage
          space for  excess  cable.  Cable  from  the junction box to
          tha transmitter should be in regid conduit and  from the
          junction box  to the probe in flexible conduit.

     3.   Refer to tfte installation shown in Figure 5.5.

     4.   In an open tank,  install a deptn (staff) gauge  in the tank
          at a location visible from the  transmitter so periodic
          checks can be made on the calibration,  zero on this gauge
          must correspond to the probe's  zero  reference.

-------
   IIS VOLT 6O HZ
   POWER SUPPLY
   SIGNAL.
   CABLE
   IN RIGID
   CONDUIT
                               MANUFACTURER'S RECOMMENDED
                               3-CONDUCTOR  TWISTED.
                               SHIELDED CABLE
                                            PROBE
                                            HEAD
                   FLEXIBLE CABLE
                   TO EASE INSPEC-
                   TION a MAINTENANCE
                      INSERTION LENGTH
                                                       MOUNTING
                                                       BRACKET
                                                       TO SUIT
                                                       THE APP-
                                                       LICATION
                                      COATING AROUND  THE
  L
NOTE(S):
  I) MOUNT THE PROBE  TO MINIMIZE
    MOUNTING THREADS.
  2) MOUNT THE PROBE  SO IT IS NOT IN THE  DIRECT STREAM
    OP A FILLING  CHUTE  OR  NOZZLE. IF  REQUIRED. USE DE-
    FLECTING  BAFFLES.
  3) USE CARE DURING  INSTALLATION TO PREVENT  ACCIDENTAL
    DAMAGE TO THE PROBE  INSULATION
Figure 5.5,   Capacitance  probe and  transmitter  installation.
                            161

-------
P.   Designer Checklist

     ASH the following questions when designing or reviewing
     capacitance level measurement applications.  All checklist
     questions should be answered "yes."

     1.   is the process stream free from heavy grease?  If not,
          capacitance probes are not recommended.

     2.   Is coating of the probe likely?  If yes, then coating
          compensation is essential.

     3.   Is the tank or tank wall grounded?  If not, then provide
          grounding.

     4.   is the probe mounted securely, without providing potential
          sites for solids buildup?

     5.   Can the probe be removed easily for inspection, cleaning,
          and calibration?

     6.   Is the meter installation designed so that it can be
          calibrated by one person?

     7.   Is the transmitter protected from the weather?

     8.   Has a depth gauge been installed for quick calibration
          checks?

G.   Maintenance and Calibration

          Task               Fr equency
          ^••MMHB                         |

     1.  Clean probe.        Depends on application.

     2.  Calibrate probe.    Once a month to once every two months.

H.   Deficiencies

     The following problems are often encountered in capacitance
     probe applications.

     1.   Coating causes meter to measure level inaccurately.  Clean
          probe more frequently.

     2.   Tank not grounded signal noise and calibration drift.

I.   References:

     1.   Liptak, B. G. and K. Venczel.  Instrument Engineers
          Handbook.  Chilton Book Company, Radnor, Pennsylvania,
          1969, Revised, 1982.

     2.   Schuler, E.  A practical Guide to RP Level Controls.
          Drexelbrook Engineering Co., Horsham, Pennsylvania,  1981.


                         162

-------
5.3  FLOAT LEVEL INSTRUMENTS

     A.   Application

          1.
          Float type level  indicators  are  often used in wastewater
          treatment plants  if  remote readout is not needed.

     2.   Float type level  switches are  generally used in wastewater
          treatment processes  for alarms and equipment on/off
          control.
             TABLE 5.4.  FLOAT LEVEL  INDICATORS
     HASTEWATER TREATMENT FACILITY APPLICATION GUIDELINE
Recommended

potable water tanks
Fuel tanks
All process streams
                                  Not Recommended
                                  Process streams
B.   Principle of Operation

     1.   Level indicator.

          A float level  indicator consists  of  a float,  an attached
          rod with pointer,  float guide  and indicator  scale.   These
          components are  shown  in Figure 5.6.   As  the  float rides up
          or down on the  liquid surface, the pointer  indicates the
          level.
              ROD
            GUIDES
            FLOAT
                                       INDICATOR SCALE
         Figure 5.6.  Simple float level  indicator.
                        163

-------
     Another  type  of float level indicator is shown in Figure
     5.7.   In tiiis case,  float movement is indicated by  the
     counterweight position.
           CONNECTING CABLE
            STILLING WELL-
                FLOAT
                                               ^- INDICATOR
                                              X;    SCALE
                                             COUNTERWEIGHT
Figure 5.7.  Counterweighted  float  level indicator.

      Floats can also be connected to transmitters  for  remote
      monitoring.  However, this arrangement is seldom  used.
      Some other type of level meter such as bubbler,
      capacitance, or sonic is used instead.

 2.    Level switch.

      Float switches depend on the liquid's bouyant force to
      activate the switch.   In one switch position  the  float  is
      bouyed up by the liquid; in the other position the float
      hangs down in the absence of liquid.

      A, wide variety of float devices exist which  translate the
      float position into electrical on/off signals. The
      Instrument Engineers' Handbook(D  nas a  summary of
      them.  Of these devices, the majority of wastewater
      treatment plant applications use  the tilt switch  type
      shown in Figure 5.8.   Each switch  is a bouyant bag with a
      mercury switch inside.  When the  bag is  tilted from one
      position to the other, the mercury switch opens or closes
      an electrical circuit.  This circuit activates a  relay to
      provide the contacts necessary for local controls and
      remote monitoring.
                    164

-------
B.
           Figure 5.8.  Float switches.

Accuracy and Repeatability

Accuracy for float devices monitoring quiescent liquids can  be
+0.6 cm (1/4 in).  Turbulence has an adverse affect on
accuracy.  Most float switch (tilt type) installations leave
8-16 cm (3-6 in) of cable between the bag and the  tie down to
allow freedom of movement of the bag for maximum sensitivity.
Turbulent conditions have been observed to cause inaccuracies
greater than 10 cm (4 in).

Solids buildup on guides and floats will degrade the accuracy
of float indicators.  Therefore, applications having potential
for turbulence or solids buildup are not recommended.

Manufacturer's Options

1.   Controller enclosure:

     a.   NEMA 12, dustproof, and

     b.   NEMA 4, weatherproof.

2.   Output:

     a.   DPDT contacts rated at 5 amp, 120 VAC.

Installation

A recommended installation method for float switches is shown
in Figure 5.9.  If turbulence is expected, also install a
stilling well.

The installation figure shows the floats permanently fixed to a
specific level.  This is true of most float switch
installations.  The switch setting cannot be easily changed, so
carefully design initial placement.

-------
    JUNCTION  BOX
                          r
                              CONDUIT RUN
                             RIGID  CONDUIT

                             CONDUIT SEAL
                            STAND PIPE-RIGIDLY FASTENED
                                        TO TANK WALL
                                  FLOAT SWITCH ASSEM8LIES-
                                 < LOCATED TO PROJECT RE-
                                  QUIREMENTS
      Figure 5.9.  Float switch mounting  installation.

F.   Designer Checklist

     The following questions snould  be  asked  when  designing or
     reviewing applications of float level  instruments.   All
     checklist questions should be answered "yes".

     1.   Will the float be bouyant  at  process  pressure?
          Temperature?

     2.   Is the float protected from turbulence?

     3.   Is the output matched to its  intended uses?

     4.   Are switch settings accurately  known?

     5.   Are switches sheltered from strong  air currents?
                       166

-------
G.   Maintenance and Calibration

     1.   Level indicators:

          Task               Frequency

     a.  Calibration.        Depends on mechanical or electrical
                             linkage to indicator.

     b.  stilling well       Weekly to bi-weekly.
         cleaning.

     2.   Level switches:

          Task               Fr equency

     a.  Inspection and      Every six months.
         operational check.

     b.  Stilling well       Weekly to bi-weekly.
         cleaning.

H.   Deficiencies

     The following problems are commonly reported for float level
     devices.

     1.   Stilling well cleaning requires too much attention.

     2.   Switches give false trips due to turbulence.

     3.   Solids buildup on the float changes the calibration.

I.   References

     1.   Liptak, B. G. and Venczel, K.  Instrument Engineers
          Handbook.  Chilton Book Company, Radnor, Pennsylvania,
          1969, Revised, 1982.

     2.   Instrumentation in Wastewater Treatment Plants; Manual of
          Practice No. 21.  Water pollution Control Federation, 1978,
                        167

-------
5.4  SONIC AND  ULTRASONIC LEVEL SENSORS

     A.    Application

          Sonic and  ultrasonic level sensors do not contact the process
          fluid; therefore, they can be used in any wastewater treatment
          process, provided that process vapors do not cause problems.
          The two most  common vapor problems are corrosion, which can be
          lessened by choice of materials, and condensate or ice buildup
          on cold sensors which can be prevented by heaters.


TABLE 5.5.  SONIC AND ULTRASONIC LEVEL SENSORS APPLICATION  GUIDELINES
     Recommended

     Open channel  flow
     Wet wells
Not Recommended
Foam
     B.    Operating  Principle  •

          The sensor periodically generates a pulse of sonic or
          ultrasonic waves that bounce off the liquids surface and echo
          back.   The echo is detected by a resonant metal disc.  Based on
          the speed  of sound or ultrasound, the time between sending and
          receiving  is measured and converted into distance which is then
          converted  to level.  See Figure 5.10.
                                          SENDER a RECEIVER
              y/////////////
                             Figure 5.10
                              168

-------
     Sonic and ultrasonic wave velocity depends on air  conditions:
     temperature, pressure and humidity.  Where changing  conditions
     are expected, automatic compensation can be provided.
     Typically, only temperature compensation is used;  temperature
     errors are about 0.2% per °c (0.17% per °F).

     Sensors are available with frequencies from about  9  kHz sonic
     to about 50 kHz (ultrasonic).  Also, the generator can have
     different shapes such as wide angle cone, narrow angle cone or
     parabolic.  Selection of frequency and sensor shape  are both
     based on the amount of attenuation expected.  ?or  example, one
     manufacturer provides:

     •    Wide angle cones for up to 3m (10 ft).

     •    Narrow angle cones for up to 10m (30 ft).

     •    Parabolic reflectors for up to 25m (80 ft).

     Signal attenuation can be caused by absorption into  the air,
     reflection away from the receiver's sensing area,  and
     absorption by foam on the liquid surface.  The cone  shapes
     listed above are selected to reduce attenuation by reflection.
     Distance and wave frequency affect attenuation by  absorption.
     As distance from the sensor to the liquid level increases,
     signal strength decreases in proportion to the distance
     squared.  Thus, if signal strength is 100% at distance  "d" when
     a tank is full, the signal strength will drop to 25% at a
     distance of *2d".

     Sonic waves attenuate less then ultrasonic.  For example, foam
     on  liquid surfaces may completely absorb ultrasonic waves.

C.   Accuracy and Repeatability

     Accuracy of _+!% of span and repeatability of +0.1% of span can
     be obtained.  Air conditions, liquid turbulence, foam and
     interfering echos from obstructions can reduce both accuracy
     and  repeatability of the sensor.

D.   Manufacturers' Options

     1.   Sensor wave frequency:

         a.   Sonic.

          b.   Ultrasonic.

     2.    Sender shape:

          a.   Wide cone.

          b.   Narrow cone.

          c.    Parabaloid.

                         169

-------
     3.   Sensor  temperature compensation.

     4.   Sensor  thermostatically controlled heater.

     5.   Sensor  air purge.

     6.   Sensor  range selection.

     7.   Indicator on transmitter.

     8.   Transmitter output:

          a.    4-20 mAdc  into 750 ohms maximum, isolated.

          b.    0-20 mAdc  into 750 ohms maximum, isolated.

     9.   Transmitter enclosure:

          a.    NEMA 1,

          b.    NEMA 4, and

          c.    NEMA 12.

E.   Installation

     1.   Range.

          Determine the range of the meter from expected conditions
          in  the  tank or  channel.  See Figure 5.11.  The mounting
          location of the sensor is then calculated from
          restrictions established by the manufacturer.   Generally,
          the sensor must be above the maximum level by  at least
          some minimum distance, usually about 50-70 cm  (18-24 in).
          In  Figure 5.11, this would correspond to an "A-MINIMCM"
          value.  The distance from the sensor to the lowest level
          measured must be less than its maximum rating  for "C*, and
          the ratio of "A:C" must be less than the manufacturer's
          specification.

          The sensor must be mounted far enough from tank walls to
          prevent false echoes.  This distance, "D", depends on
          sender  shape.   Calculations for correct sensor location
          will differ for each mam-'acturer.
                         170

-------
                                                .100% FULL-
                                                 0% FULL
A = Distance from generator/ceceiver to 100% full level.

B « Measured range,  distance from 0 to 100% full.

C » A & B.

D * Distance from tank  wall.

Manufacturer's set  limits on dimensions of "A", "C", "D* and the ratio of "A"
to "a."


                     Figure 5.11.  Installation dimensions.

               2.   Stilling well.

                    A stilling well is used with sonic/ultrasonic sensors to
                    dampen out liquid level turbulence, reduce foam, increase
                    signal strength (essentially producing a cylindrical-
                    shaped sensor), eliminate noise from icray echos or to
                    lessen condensate problems.  When used, the stilling well
                    should be cut from a single length of PVC pipe 15-20cm
                    (6-8 in.) in diameter.  The bottom end should be cut at a
                    450 angle.

                    Drill air relief holes near the top where the sensor is
                    attached.
                                  171

-------
          Keeping the stilling well clean is a must; accumulated
          solids can cause echos that she transmitter will read as
          liquid level.  Therefore, provide for either manual or
          automatic washdown of the well interior wall.

     3.    Transmitter.

          The  transmitter location depends on the intended method of
          calibration.  The transmitter may be remotely located as
          much as 200m  (700 ft) away provided that:

          a.    The sensor is equipped '• -th a calibration bar, or

          b.    The tank can be isolated from feed and exit streams
               and the  level manually raised (or lowered) , or

          c.    The liquid level in the tank can be manually observed
               at the transmitter location by an independent method.

F.   Designer  Checklist

     Ask the following questions when reviewing or designing a sonic
     ultrasonic level meter application.  All answers should be
     "yes."

     1.    Is temperature compensation provided?  If not, is the
          degraded accuracy acceptable?

     2.    Is condensation unlikely to occur on the sender/receiver?
          If it is likely, then is an air purge and/or heater
          provided?

     3.    Can  a stilling well be avoided?

     4.    Can  the sensor be mounted so that the full range of
          expected levels are within the manufacturer's
          specifications for minimum and maximum distances?

G.   Maintenance and Calibration

          Task              Frequency

     1.   Calibration.        Every two months.

     2.   Check temperature   Every two months.
         compensation.

     3.   Stilling well       Depends on process stream.
         clearing.
                         172

-------
H.   Deficiencies

     The following problems have been reported for. sonic and
     ultrasonic level meter installations.

     1.    Stilling well causes interfering echos from pipe joints or
          deposited  solids or grease.  Maintaining a clean stilling
          well is difficult.

     2.    Meter does not  read on cold days because receiver is
          covered with ice.
                         173

-------
6.0  ?S ES S UR S M E AS OR El S NT



     S.I  PRESSURE CELLS

          A.   Application
               Pressure meters are applied to enclosed process lines such as
               compressed air distribution systems, pump discharges, and
               tanks.  With the aid of isolation diaphragms, pressure
               transmitters can be successfully applied to any wastewater
               treatment process.
            TABLE 6.1.  PRESSURE MEASUREMENT APPLICATION GUIDELINE
          Recommended                  Recommended with Isolation Diaphragm

          Air                          Chlorine
          Oxygen and ozone             Wastewater with s»lids
          Digester gas                 Sludge
          Water
         -Secondary effluent

          B,   Principle of Operation

               1.   Mechanical pressure elements.

                    The three most common elements used to indicate pressure
                    are:  Bourdon tubes, bellows, and diaphragms.  In each
                    case process pressure causes the element to move in
                    proportion to the pressure applied.  This motion is
                    amplified by a mechanical linkage connected to a pointer
                    and dial or by electronics to a voltage or current
                    signal.  Schematic, diagrams of each type are- shown in
                    Figure 6,1.

                    a.   Bourdon tube.

                         A Bourdon tube is a curved tube sealed at the tip.
                         As process pressure increases inside the tube,  the
                         tube will straighten causing the tip to deflect.
                         The deflection is transferred to a dial indicator
                         by mechanical linkage.  Besides a C-shaped tube,
                         Bourdon tubes are available in spiral, twisted, and
                         helical forms, round, oval or rectangular in cross
                         section.
                                    174

-------
                      BOURDON
                      C-TUBE-.
                                                        DIAL
                                              MECHANICAL
                                              LINKAGE
                                    PROCESS
                                    PRESSURE
MECHANICAL
LINKAGE
                           DIAL
MECHANICAL
LINKAGE
                            RESTORING
                              BELLOWS
                PROCESS
               PRESSURE
                                                                         DIAL
                                                                          DIAPHRAM
                PROCESS
               PRESSURE
                Figure 6.1.  Mechanical pressure elements.

                  b.   Bellows.

                       Bellows elements are deeply corrugated metal
                       cylinders closed at one end.  Process pressure
                       applied to the bellows causes it to expand.
                       Bellows expansion is transferred to a dial
                       indicator by mechanical linkage.  Bellows are also
                       configured to contract on increasing pressure,  in
                       some cases restoring springs are added to increase
                       operating range or to reduce element wear.
                                  175
                O

-------
     c.    Diaphragms.

          Diaphragms  are metal disks, either flat or
          concentrically corrugated.   Process pressure
          applied to  one side causes  the diaphragm to deflect
          outward.   Diaphragm deflection is transferred to a
          dial indicator by mechanical linkage.   Corrugated
          diaphragms  are capable of greater deflection and
          are more linear than flat diaphragms.

2.    Electro-mechanical  elements.

     Electric signals  proportional  to pressure are obtained
     by  mechanically  connecting an  electrical component such
     as  a capacitor,  strain gauge,  or inductor to a
     diaphragm.   Deflection of the  diaphragm will change the
     associated electrical property,  e.g.,  distance between
     plates in a capacitor, piezoelectric response, and loop
     reluctance.

     In  some elements  a  restoring force is  applied to the
     diaphragm to keep it undeflected.  This eliminates
     nonlinearity due to diaphragm  deflection.  The restoring
     force is measured electrically and converted to
     pressure.  These elements are  called force-balance
     transducers.

3.    Gauge, differential, and absolute pressures.

     Gauge, differential, and absolute pressures may be
     measured by any  pressure element depending  on the
     reference pressure.  Gauge pressure is measured using
     atmospheric pressure as reference.  In this case,
     Bourdon tubes, bellows and diaphragms are constructed to
     have access to the atmosphere on the side opposite the
     process connection.

     See Section 6.2  for information  on differential pressure
     and absolute pressure elements.

4.    Vacuum measurement.

     Vacuum pressures for slight vacuums, to -90 kPa, can be
     measured with elements similar to those discussed
     above.  At low vacuums these elements become inadequate
     because of gravitational interference in force
     measurement near zero atmosphere.  Usually, low vacuums
     are measured indirectly from some other property of gas
     such as thermal  conductivity,  viscosity, or the behavior
     of gas during ionization or electrical discharge.  Low
     vacuums are not monitored in wastewater treatment
     therefore, their measurement is not explained here.


                      176

-------
C.    Accuracy and Repeatability

     Quartz Bourdon tubes can be accurate to £0.01% of span, which
     is as accurate as a quality manometer.  On-line pressure
     transmitters are accurate to better than +0.5% of span.
     Pressure gauges are typically accurate to +1 to 2% of span.

     Typically, repeatability of measurement is about one-fifth of
     the stated accuracy.

D.    Manufacturer's Options

     1.   Ranges - almost any range is available,

     2.   Materials (wetted):

          a.   Brass,

          b.   Bronze (or phosphor bronze),

          c.   Beryllium copper,

          d.   Stainless steel,

          e.   Monel, and

          f.   Hastelloy-C.

     3.   Transmitter output signals:

          a.   4-20 mAdc into 650 ohms,

          b.   10-50 made into 250 ohms, and

          c.   1-5 VDC isolated.

     4.   Power:

          a.   Two-wire transmitters are the most common
               configuration; they require external 12 Vdc or 24
               Vdc power supplies, and

          b.   Four-wire transmitters  which require line power
               (115 VAC, 60 Hz).

     5.   Transmitter enclosure:

          a.   NEMA 4, and

          b.   Explosionproof.

     6.   Isolation diaphragms of the  same wetted materials listed
          for the elements are available from some manufacturers.
          Diaphragm,  transmitter, and  connection line can be
          furnished as a complete assembly.

                          177

-------
E.    Installation

     1.    Install the transmitter  in an  environment that meets the
          specifications  listed by the specific manufacturer.
          This is usually -20 to 65oc (0-15QO?)  and 0-95%
          relative humidity.   Zero and span will shift with
          ambient temperature,  so  avoid  temperature extremes or
          calibrate at conditions  equal  to the installed
          environment,

     2.    Install the transmitter  as close as possible to the
          process measurement site.   This will reduce response
          time which can  be important in flow control or level
          control applications.  The installation must allow good
          maintenance access.  In  some cases it will not be
          practicable to  install the transmitter to meet both
          nearness and maintenance criteria.  In these situations,
          control requirements  must be given first priority.

     3.    Connect meter runs  to liquid process lines
          horizontally.  This will minimize the amount of solids
          and gas entering the  connection.  Entrapped gas will
          decrease response time and solids may plug the meter
          connection.  Slope  meter runs  8 on per meter (1 in. per
          foot) of run so that  gas bubbles bleed back into the
          process line.

     4.    Connect meter runs  to gaseous  process lines at the top
          of pipes or tanks to minimize the amount of solids and
          moisture entering the connection.  Slope meter runs at
          least 8 cm per  meter  (1  in. per foot) of run so that
          condensation will drain  into the process line.  Any low
          spots in the meter  run will require a condensate
          collection pot.  Heat trace meter runs on condensable
          gases.  Entrapped liquids may affect meter accuracy and
          may cause accelerated corrosion.

     5.    For applications where the measured liquid contains
          solids, flushing provisions or diaphragm isolation may
          be needed.  Diaphragm connections to the process should
          be a minimum of 2.5 on (1 in.) for sludge lines and 1.3
          cm (0.5 in.) diameter for other wastewater lines.

     6.    Install an isolation valve at the process measurement
          connection on all meter  runs.   If this valve is not
          readily accessible for maintenance, install another
          isolation valve at the transmitter.  See Section 6.2 for
          manifold requirements.

     7.    Materials recommended for harsh environments are:

          a.   Chlorine - Hastelloy-C, and

          b.   Digester gas - 316  stainless steel.

                          178

-------
?.   Designer Checklist

     Ask the following questions when designing or reviewing
     pressure meter applications.  All checklist answers should be
     "yes."

     1.   Is the meter situated for adequate response time and
          good maintenance access?

     2.   Are meter runs installed to keep out interfering
          substances?

     3.   Can the meter be calibrated in place?

     4,   Is the meter in a suitable environment?

G.   Maintenance and Calibration

          Task               Frequency

     1.  Calibration.        Every three to six months.  Meters
                             used  in critical control applications
                             may need more frequent calibration.

H.   Deficiencies
                                   •
     The following problems are commonly reported for pressure
     transmitters:

     1.   Meter  installed in an inaccessible location,

     2.   Meter  runs  incorrectly installed, and

     3,   Diaphragms  or flushing not provided on sludge lines.

I.   References

     1.   Gillum, Donald R.  Industrial Pressure Measurement.   ISA
          Publications, 1982,

     2.   Hewson, John E.  Process Instrumentation Manifolds.   ISA
          Publications, 1981.

     3.   Measurement & Control Pressure/Force Handbook and Buyers
          Guide, 1983.  Measurements & Data Corporation, 1982.
                          179

-------
5.2  DIFFERENTIAL SRSSSURE

     A.    Application
          Differential pressure transmitters,  £p cells,  are used with
          primary elements to measure flows,  gauge pressure, and liquid
          level.   With the aid of isolation diaphragms or purge
          systems, -p cells can be successfully applied  to any
          wastewater treatment process.
      TABLE 6,2.  DIFFERENTIAL  PRESSURE APPLICATION GUIDELINE
     Recommended                  Recommended with Isolation Diaphragm

     Air                          Chlorine
     Oxygen and ozone             Wastewater with solids
     Digester gas                 Sludge
     Water
     Secondary effluent

     B.   Principle of Operation

          1.   Mechanical pressure elements.

               The three most common elements used to indicate pressure
               are:  Bourdon tubes, bellows, and diaphragms.  In each
               case, the element moves in proportion to differential
               pressure.  This motion is amplified by mechanical
               linkage to a pointer and dial.  Schematic diagrams of
               each type are shown in Figure 6.2.

               a.   Bourdon tube

                    A Bourdon tube is a curved tube sealed at the tip.
                    As process pressure increases inside the tube, the
                    tube straightens, causing the tip to deflect.  The
                    deflection is  indicated on a dial by mechanical
                    linkage.  Besides a C-shaped tube, Bourdon tubes
                    are available  in spiral, twisted, and helical
                    forms, round, oval, or  rectangular  in cross section.

               b.   Bellows.

                    Bellows elements are deeply  corrugated metal
                    cylinders closed at one end.  Process pressure
                    applied to the high side of  the bellows causes it
                    to expand.  Bellows expansion is converted to
                    pointer and dial indication.  Bellows are also
                    configured to  contract  on increasing pressure.   In
                    some cases restoring springs are added to increase
                    operating range  or  reduce element wear.
                               180

-------
             HIGH
                                                         DIAL
                   DIAL-
HIGH
LOW
                                    MECHANICAL
                                    LINKAGE
                                                                      DIAL
                                                         HIGH
                                                                 LOW
     Figure 6.2.  Mechanical differential pressure elements.

             c.   Diaphragms

                  Diaphragms are metal discs, either flat or
                  concentrically corrugated.  High and low  process
                  pressures are applied  to opposite sides of the
                  diaphragm.   This causes the diaphragm to  deflect.
                  A mechanical linkage connects the diaphragm to a
                  pointer  for  dial indication.  Corrugated  diaphragms
                  allow  larger deflection and better linearity than
                  flat diaphragms.
                             181

-------
     2.    Electro-mechanical elements.

          Electric signals proportional to differential pressure
          are obtained by mechanically  connecting an electrical
          component such  as a capacitorf  strain gauge,  or inductor
          to a diaphragm.   Deflection of  the diaphragm will change
          the associated  electrical property, e.g.,  distance
          between plates  in a capacitor,  piezoelectric response,
          and loop reluctance.

          In some elements a restoring  force is applied to the
          diaphragm to keep it undeflected.  This eliminates
          nonlinearity due to diaphragm deflection.   The restoring
          force is measured electrically and converted to
          differential pressure.   These elements are called
          force-balance transducers.

     3.    Absolute pressure elements.

          Absolute r-<2ssure elements are differential pressure
          elements with the low pressure side evacuated to -101.3
          kPa and sealed  from atmosphere.

C.    Accuracy and Repeatability

     Quartz Bourdon tubes have reported accuracies of _+0.01% of
     span, which is equal to the accuracy of a good quality
     manometer.  On-line  differential pressure transmitter
     accuracy is equal to or better than +_0.5% of span.
     Differential pressure gauges typically have accuracies of
     0,5% to 2% of span.

     Repeatability of measurement for differential pressure gauges
     and transmitters is  commonly about one-fifth of the rated
     accuracy.

D,    Manufacturer's Options

     1.    Ranges - almost any range is  available,

     2.    Materials (wetted):

          a.   Brass,

          b.   Bronze (or phosphor bronze),

          c.   Beryllium copper,

          d.   Stainless steel,

          e.   Monel, and

          f.   Hastelloy-C.

                          182

-------
     3.    Transmitter  output  signals:

          a.    4-20  mAdc into 650  ohms,

          b.    10-50 maCC into 250 ohms,  and

          c.    1-5 VDC isolated.

     4.    Power:

          a.    Two-wire transmitters  are  the most  common;  they
               require a separated 12 Vdc or 24 Vdc  power  supply,
               and

          b.    Four-wire transmitters which  require  line power
               (115  VAC, 60 Hz).

     5.    Transmitter  enclosure:

          a.    NEMA  4,

          b.    Explosionproof, and

          c.    Both  available with insulated jackets or  boxes.

     6.    Isolation  diaphragms of  the same wetted  materials are
          available  from some manufacturers.  Diaphragms,
          transmitter, and connection line can be  furnished as a
        •  complete assembly.

     7.    Square root  extractor.

     8.    Scales:

          a.    Linear, and

          b.    Square.root.

E.    Installation

     1.    Install the  transmitter  in  an  environment  recommended by
          the manufacturer.  This  is  usually -20 to  65Oc
          (0-150°F)  and 0-95% relative humidity.  Zero and span
          will shift with changes  in  temperature,  so avoid
          temperature  extremes.

     2.    Install the  transmitter  as  close as possible to the
          process measurement site to reduce response time which
          can be important in flow control or level  control
          applications.  The  installation must allow easy access
          for maintenance. In some cases it will  not be practical
          to  install the transmitter  to  meet both  nearness and
          maintenance  criteria.  In these situations, control
          requirements must be given  first priority.
                          183

-------
3.    For solids bearing liquid process lines connect meter
     runs horizontally, do not connect meter runs to the
     upper quadrant of the pipe.   This will minimize the
     amount of solids and gas entering the connection.
     Entrapped gas will decrease response time, and solids
     may plug the meter connection.   Slope meter runs 8 cm
     per meter (1 in. per foot) of run so that gas bubbles
     bleed back into the process  line.

4.    Connect meter runs to gaseous process lines at the top
     of pipes or tanks to minimize the amount of solids and
     moisture enteri g the connection.  Slope meter runs at
     laast 8 cm per meter (1 in.  per foot) of run so that
     condensation will drain into the process line.  Low
     spots in meter runs should be avoided.  If they cannot,
     add drain pots to these low spots.  Heat trace meter
     runs on condensable gases.  Entrapped liquids will
     affect meter accuracy and may cause accelerated
     corrosion.

5.    Special precautions must be taken in steam applications
     to prevent overheating of the manifold and transmitter.
     Side mount pressure taps to allow steam into the tap
     while still allowing drainage of excess condensate back
     into the process pipe.  A condensate pot should be
     installed on each meter lead.  To avoid overheating,
     blowdown valves should not be incorporated in the
     manifold.

     In steam applications, a water seal is required between
     the condensate pot and the manifold.  This prevents
     steam from reaching the manifold and transmitter and
     prevents uncontrolled buildup of condensate in the meter
     leads.  The condensate pots must be identical in size,
     the same height above the transmitter, and self-draining
     to the process pipe.

6.    For applications  involving solids bearing liquids,
     flushing provisions or diaphragm isolation may be
     needed.  Diaphragm connections to the process should be
     a minimum of 2.5 cm (1 in.) for sludge lines.

7,    Install an  isolation valve on all meter runs at the
     process measurement site  (pressure tap), and except for
     very short  tap lines, at  the transmitter.

8.   Materials recommended for harsh environments  are:

     a.   Chlorine  - Hastelloy, and

     b.   Digester  gas - 316 stainless steel.
                      184

-------
    INSTRUMENT
  EQUALIZE
IMPULSE PIPE
OR TUBING
                                                          CALIBRATION a
                                                          TEST
                        INSTRUMENT
                         TEST PORTS
                                PLUG
                              ISOLATION
                            PROCESS
                                                         EQUALIZE
IMPULSE PIPE
OR TUBING
                                                                                  ISOLATION
                                                                                 PROCESS
  INSTRUMENT
   EQUALIZE
       PROCESS—^
                           TEST PORTS
                               PLUG
                              ISOLATION
                                  IMPULSE PIPE
                                  OR  TUBING
                                                      CALIBRATION  a
                                                      BLEED
                                                                               INSTRUMENT
                                                       EQUALIZE
                                                   IMPULSE PIPE
                                                   OR  TUBING
                                                   SLOWDOWN
                                                                                     ISOLATION
                                                                               PROCESS
                                   Figure  6.3.  Manifolds.
                                            185

-------
9.    Differential pressure transmitters are usually installed
     with valves that enhance some combination of instrument
     calibration, blowdown of accumulated material in the
     metec piping, and isolation of the transmitter.  An
     economic way to provide the desired functions is to use
     factory-made valve manifolds.  Some common manifolds are
     shown in Figure 6.3.   Available manifold options are:

     a.    Number and configuration of valves:

          1)    3-valve:   isolation and equalization,

          2)    5-valve:   isolation, equalization, and
               calibration,

          3)    5-valve:   isolation, equalization, and
               blowdown,  and

          4)    7-valve:   isolation, equalization,
               calibration,  and blowdown.

     b.    Process connections:

          1)    Pipe:  1/2" NPT  female and 3/8" MPT female,  and

          2)    Tube:  3/8" and  1/2".

     c.    Transmitter connections:

          1)    Pipe:  1/2" NPT  female,

          2)    Direct - flanged, and

          3)    Tube:  3/8" and  1/2".

     d.    Materials of construction:

          Same selection as  for transmitter.

     e.    Remote zeroing:

          1)    Motor operated 3-valve manifold.

     Wastewater treatment applications typically use 3-valve
     manifolds which implies that a check of meter zero is
     sufficient and that a check of the span is not required
     at a frequent enough interval to justify the expense of
     a more complex manifold.  Span calibration test
     frequencies of three to six months for most applications
     confirms this practice.  Where Ap cells are part of a
     flow measurement system used as a standard, or for
     billing purposes, the frequency of calibration and
     testing may be much more often.  In such cases it is
     recommended that 5-valve manifolds be installed to
     reduce calibration setup time.
                     186

-------
     10.  A common use of -ip cells is with primary flow elements
          to measure pressure-drop for flow calculation.

          Special installation practices foe flow applications are
          presented with the primary device, see orifice meters,
          venturi meters.

     11.  Another common usage of Ap cells is to measure liquid
          levels.  Two general methods are used:  hydrostatic head
          and bubbler (dip tube).  Bubbler installations are more
          common in wastewater treatment processes; they are
          discussed in Section 5.1.  Figure 6.4 shows typical
          hydrostatic level installations for an enclosed tank.
          The tank is covered, so the A p cell must use the
          pressure of the vapor phase as a reference.  The Ap cell
          is at the same level as the bottom pressure tap, and the
          connection to the top tap is vapor filled or "dry."
          Thus, the difference in pressure is proportional to
          liquid level.  If the tank was open, a plumbing
          connection to the reference side of the dp cell would
          not be necessary.  The Ap cell would just need to be at
          the same ambient pressure,  i.e., in the same room with
          the tank or both the Ap cell and the tank outdoors.

          A "wet leg" configuration for level measurement is shown
          in Figure 6.5.  The reference side of the Ap cell is
          filled with a liquid.  It does not have to be the same
          as the tank liquid.   If the liquid is not the same, the
          difference in specific gravity of the two liquids must
          be used to correct the meter calibration.  The liquid in
          the wet leg prevents unwanted accumulation of condensate
          at the reference side.   In  this configuration the
          reference (wet leg)  is connected to the low-pressure
          side of the Ap cell, just as in a dry leg setup.  As
          shown, the meter would read -100% at '0'  liquid level
          and '0'% at 100% liquid level.  This is corrected during
          calibration by supressing zero to provide a correct tank
          level indication.

F.   Designer Checklist

     Ask the following questions when designing or reviewing
     differential pressure meter applications.   All checklist
     answers should be "yes,"

     1.    Is the meter situated for adequate response time and
          good maintenance access?

     2,    Are meter runs installed  to keep out  interfering
         i substances?

     3,    Can the meter  be calibrated in place?

     4.    Is the meter  in  a suitable  environment?
                          187

-------
   VAPOR
   LIQUID
                     VALVES IN OPERATING MODE
                     X OPEN     >-^CLOSED
                         GAGE GLASS
                                        AP
                                       TRANS
n
                           -tx-
               Figure 6.4.   Dry leg.
VAPOR
LIQUID
                 VALVES IN OPERATING  MODE
                  X OPEN    >~4 CLOSED
                      GAGE GLASS
                                     AP
                                    TRANS
                        -cx-
                                                    FILL
                                                        WET LEG
                                                      LVENT
               Figure 6.5.  Wet  leg.
                      188

-------
G.   Maintenance and Calibration

          Task               Frequency

     1.   Calibration.         Every three to six months.  Meters
                             used in critical control applications
                             may need more frequent calibration.

H.   Deficiencies

     The following problems are commonly reported for pressure
     transmitters:

     1.    Meter installed in an inaccessible location,

     2.    Meter runs incorrectly installed, and -

     3,    Diaphragms or flushing not provided on sludge lines.

I.   References

     1.    Hewson, John E.  Process Instrumentation Manifolds.  ISA
          Publications, 1981.

     2.    Manual on Installation of Refinery Instruments and
          Control Systems,  Part I - Process Instrumentation and
          Control, Section  1 - Flow, and Section 2 - Level.
          American Petroleum Institute, 1974.

     3.    Measurement & Control Pressure/Force Handbook and Buyers
          Guide, 1983.   Measurements & Data Corporation, 1982.
                          189

-------
PERFORMANCE TESTING


7.1  FLOW

     A.   General

          Perform quality assurance testing  to  satisfy stipulated
          acceptance requirements  and  to  provide  a  cal* Cation
          reference point for  a  particulai flow meter.   Perform
          quality control monitoring as an on-going practice  to
          maintain a continuous  indication of meter reliability.

          1.   Even if a flow  meter is factory  calibrated  prior  to
               delivery, perform an in-place calibration when the
               meter is first  installed to satisfy  the stimulated
               acceptance requirements and to establish a
               calibration reference to use  for quality control
               monitoring and  periodic maintenance  calibration.  Two
               types of calibration procedures  are  presented:

               a.   Hydraulic  calibration.

               b.   Non-hydraulic  calibration.

          2.   Prior to calibration, be sure that the flow meter is
               properly installed  and  that it is  given a preliminary
               checkout according  to the  manufacturer's instructions.

     B.   Non-Hydraulic Calibration

          1.   During the process  design  phase, layout equipment and
               piping to allow in-place hydraulic calibration and
               acceptance testing  for  all flow  meter installations.
               In certain situations this may not be feasible, and
               calibration testing may be performed using
               "simulator-type"  calibration  equipment offered as an
               option by many  meter/transmitter manufacturers.

          2.   Use the simulator method of calibration only when
               complete hydraulic  testing cannot  be performed and
               when there is no  uncertainty  about the proper
               operation and performance  of  the primary metering
               device.  Obtain agreement  from all parties  involved
               as to the validity  of this type  of testing  before
               acceptance.

          3.   With simulator-type calibration, the flow signal
               produced by the primary metering element, is
               simulated and input to  the converter/transmitter  to
               set the zero and  span.


                                190

-------
C.   Hydraulic Calibration

     1.   Zero the meter and correct any offset according to
          manufacturer's calibration instructions.

     2.   Set up a flowrate through the meter that  is within
          the anticipated working range (design range)  of
          flows.  Allow enough time for flow to become steady,
          then measure the reference or "true" flowrate (£%)
          using one of the methods in Part C of this section.
          During the time Q% is being measured, measure the
          indicated flow rate through the meter. Use this
          flowrate (Q) to calculate the percentage"of error
          utilizing the following equation:
               %Error  =  (Q -  QO/&  X  100
          Utilize the above procedure for a minimum of three
          flowrates, low, medium and high, within the design
          range of the meter.  Next, plot the calculated
          percentage error against the reference flowrate, Cft
          (additional test runs are recommended to ascertain
          the repeatability of the meter) .  Between each test
          run, perform a zero check to determine any short term
          drift.

          Also, calculate and plot the percentage error in
          measuring  ^ vs. CR on the same plot.  These
          values will depend upon which reference method in
          Part D is used and may be referenced elsewhere (2 -
          9).

          Next, draw a curve between the points of each of the
          percentage error groups (Q and ^).  if the
          percentage difference between the curve for  Q and
          Ql is greater than the accuracy stipulated for that
          type of meter  (as noted in previous sections of the
          handbook or alternative specifications), the
          performance of the meter may be unsatisfactory and
          the following options should be considered:

          a.   If the plot shows a constant percentage error
               for  Q, a span adjustment at the meter
               transmitter is required following the
               manufacturer's instructions.  Repeat the testing
               to verify correct span.
                            191

-------
          b.    If meter  performance  cannot  be  adjusted  to  meet
               purchaser's  specifications,  repair  or  reject
               under acceptance stipulations.

          c.    If meter  data  differences  can be  ascribed to
               non-ideal installation conditions (e.g.,
               inadequate approach piping for  mag  meters)  and
               the data  is  otherwise repeatable, the  results of
               the calibration  tests can  be used to develop a
               new, in-place  reference for  the meter.

     6.    Regard the preceding  error comparison  method
          described above as  a  suggested  procedure, only.   Other
          comparison procedures agreed to by the involved
          parties may be used to carry out  initial calibration
          and acceptance testing.  The main consideration  for
          any comparison scheme, however, is to  use the
          reliability (percentage error)  of the  reference
          measurement to determine the accuracy  of the  tested
          meter.

D.   Flow Measurement Methods for Hydraulic Calibrations

     1.    The following  general methods for measuring reference
          flow (Qjj) used in determining the measurement
          accuracy of hydraulically  tested  flow  meters  are
          briefly described:

          a.    Volumetric.

          b.    Comparison with  a reference  flow  meter.

          c.    Dilution.

          d.    Salt velocity.

          e.    Velocity area.

          These methods vary in difficulty  and in  accuracy.
          The method selected will be determined by  the type of
          meter being calibrated, the type  of  liquid  being
          measured, and the resources available  to conduct the
          test.

     2.    Volumetric calibration.

          The feasibility of the volumetric calibration
          (drawdown) method depends  primarily  on the
          availability of suitable tank space  and connecting
          conduits.  Important  considerations  for  this  method
          are:
                            192

-------
     a.    Conduct the test using  the  process  liquid  to be
          measured under  normal  flow  meter  operation.

     b.    This method is  very suitable  for  measuring
          wastewater  sludges.

     c.    The potential accuracy  of this method  is high.

     d.    The tank should be  regularly  shaped so its
          volume can  be calculated within acceptable
          limits of accuracy.

     e.    The tank volume should  be large enough to
          provide a test  run  long enough to make start and
          finish timing errors, negligible.

     f.    The change  in liquid level  in the tank should be
          enough so that  starting and finishing  depths can
          be measured without introducing significant
          error.

     g.    The flow rate should remain relatively constant
          during the  test run.

     Estimating the percentage error  for this testing
     method should include an estimate  of errors
     introduced due to physical mesurements of tank
     volume, depth change, and the elapsed  time  of the
     test.

3.   Comparison with  a reference  meter  (transfer meter).

     a.    A reference meter so described is a
          flow-measuring  device whose performance
          characteristics can be  referenced to published
          standards or to recommended practices  acceptable
          to involved parties. Examples include:

          1)   Standard venturi  tubes and venturi nozzles
               (2,3,4).

          2)   Orifice plates (2,3).

          3)   Parshall flumes (4,5).

          4)   Thin plate weirs  (5).
                      193

-------
     b.    Important considerations  regarding  this method
          include:

          1)    The  flow meter(s)  used  as  reference devices
               must meet all requirements of  accepted
               standard practices in  fabrication
               installation and  use.   In  most wastewater
               treatment plant applications,  conformance
               to these requirements,  especially for
               installation and  use,  is difficult.

          2)    Use  of differential  pressure type flow
               meters requires pressure differential
               measurement with  a U-tube  mercury manometer.

          3)    When standard weir or  flume methods are
               used, a point gauge  must be used for head
               measurement.

4.    Dilution method.

     a.    With the  dilution method  the flow rate is
          deduced from the dilution of measurable
          properties of tracer chemicals  added to the flow
          (turbulent) in known amounts.   The  tracer can be
          injected  either in a constant rate  or in a
          one-shot  slug.  The  constant-rate method is more
          suitable  in wastewater treatment plant
          applications.  Consult reference 7  for greater
          detail of this method.

     b.    In the constant-rate injection  method, a tracer
          solution  of accurately known concentration is
          injected  upstream at a constant, accurately
          measurable, rate. At  a downstream  distance
          sufficient to achieve  complete  mixing and a
          steady-
          state tracer concentration,  the flow is
          sampled.   The tracer concentration  is determined
          and used  to calculate  the flow  rate (6).

     c.    Important considerations  regarding  this method
          include:

          1)    The  tracer property  measured must be
               conservative.   Rhodamine WT has been used
               successfully in raw  sewage, however, its
               behavior in sludges  is not known.
                       194

-------
          2)    Accurate measurement must be  made of  the
               rate at which  the  tracer  is added,  and  the
               initial and final  concentrations of the
               tracer.

          3)    A high sensitivity spectrophotometec  is
               required for this  method.

5.    Salt-velocity method.

     a.    In  the salt-velocity method, bcine is injected
          suddenly at an upstream station in such  a  way
          that it rapidly becomes distributed across the
          pipe section.   The  time of passage of the  salt
          pulse between two downstream stations is
          measured by conductivity-sensitive electrodes.
          The flowrate may then be determined if the
          volume of the conduit between  the  electrodes is
          accurately known.   Consult References 3  and  8
          for details.

     b.    Important considerations regarding this  method
          include:

          1)  •  The best attainable accuracy  for this
               method is 1%.

          2)    The process liquid being.measured must  have
               a significantly smaller conductivity  than
               the brine solution.

          3)    The method is  not  satisfactory for  use  with
               raw sewage or  sewage sludges  because  of
               conductivity fluctuations; however, it  is
               suitable for treated effluent.

6.    Velocity-area method.

     a.    This method is applied  to a flow cross-section
          by  measuring a number of velocities over the
          section, each representative of the average
          velocity within an  incremental area, and then
          summing the resulting velocity-area products.
          This method can be  applied to  both open  and
          closed conduit flows; but it is more
          conveniently employed in accessible open
          channels.  Consult  Reference 9 for further
          information.
                      195

-------
          b.    Important aspects  of  this method  include:

               1)    The individual velocity components can be
                    measured  by point velocity measuring
                    instruments,  e.g.,  current meters, pitot
                    tubes,  or by  acoustic velocity meters that
                    measure an average velocity  component along
                    a line  path.

               2)    The point velocity meters are intrusive and
                    may not work  well with raw sewage and
                    sewage  sludges.

               3)    The velocity  sampling requirements are
                    lengthy and this method  is suitable only
                    where long periods of steady flow are
                    available.

E.   Performance Monitoring

     1.   In  addition to carrying out acceptance and
          calibration testing, conduct performance monitoring
          on  an on-going basis for  those flow meters which
          provide a flow rate value  important to plant
          operation (this would include almost every flow meter
          in  a wastewater treatment  facility).   Performance
          monitoring can provide  plant personnel with a quick
          indication of meter performance by using a secondary
          instrument which measures  the flow to  an intermediate
          accuracy of 5 to 10% of the actual  flow.   Types of
          measurements which  can  be  used for  flow meter
          performance monitoring  include:

          a.    Measuring pressure difference.

          b.    Manufacturer-prepared rating  curves and  tables.

     2.   Measuring pressure  difference.

          a.    Measuring of a pressure difference at a  location
               where the flow rate has a unique  and  repeatable
               relationship to the  primary  flow  meter provides
               a common and adequate means  for monitoring meter
               performance.  The  pressure difference may be
               measured around any pressure  differential-
               causing hydraulic  element, with 90° pipe
               elbows being most  commonly used.
                            196

-------
b.   This type of monitoring should be available
     prior to acceptance and calibration testing of
     the primary flow meter, so that a relationship
     between the pressure monitor and the flow rate
     indicated by the meter can be established from
     the testing results.

c.   Consider the following for the use, placement,
     and operation of pressure taps to monitor
     pressure difference.

     1)   Mount the taps so they are flush with the
          pipe inner surface and free of burrs.

     2)   Hole diameter is not extremely critical;
          diameters from 1/64 inch (0.5 cm)  to 3/8
          inch (1.0 cm) for small to large pipes are
          usually adequate.

     3)   Install the taps along the  axial canter of
          pipe elbows.   For other locations,  install
          them both up- and downstream of the device
          producing the pressure difference.
     4)   Multiple taps with piezometric rings are
          not recommended for use with typical
          wastewater treatment process streams; use
          single taps, placed upstream and downstream.

     5)   Locate single taps in horizontal or
          near-horizontal process lines in a
          horizontal diametric plane to minimize gas
          and/or solids entry into the measurement
          lines.

d.   Consider the following aspects of the
     differential pressure sensing device and
     connecting manometer tubing when setting up the
     monitoring system:

     1)   When U-tube manometers are used the medium
          selected should be appropriate for the
          magnitude of the pressure difference
          expected, e.g., water-air for small
          differentials and water-mercury for large
          differentials so that a minimum deflection
          of 3 inches should be maintained.
                  197

-------
               2)    When commerical differential pressure cells
                    are used,  they should be  frequently
                    calibrated to a liquid column manometer.

               3)    Route manometer (tap line)  connecting
                    tubing from the tap location to  the sensing
                    device to  avoid accumulation of  gasses
                    and/or solids, «.g.,  sloping horizontal
                    lines, bleed valves at high points, etc.

               4)    The connecting tubing should be  corrosion-
                    resistant  with a nominal  diameter  of 3/8
                    inches.  Provide it with  valving to
                    facilitate periodic flushing.

     3.   Manufacturer prepared rating curves and tables.

          Approximate flow measurements suitable for
          performance monitoring may also be  obtained  from
          manufacturer-prepared pump rating curves and flow vs.
          angle of opening data for 'butterfly valves.   These
          measurements would be subject to inaccuracies caused
          by installation and/or operational  factors but none
          the less provide an  easy means of ascertaining gross
          meter inaccuracies.

F.   References

     1.   National Bureau of Standards.  Recommenced Practice
         'For The Use Of Electromagnetic Flow Meters In
          Wastewater Treatment Plants.  EPA,  Municipal
          Environmental Research Laboratory,  Cincinnati, Ohio,
          August, 1980.

     2.   International Standards Organization.  Measurement  of
          Fluid Flow by Means  of Orifice Plates, Nozzles and
          Venturi Tubes Inserted in Circular  Cross-Section
          Conduits Running Full.  ISO/DIS 5167, draft revision
          of R781, 1976.

     3.   American Society for Testing and Materials.   Standard
          Methods of Flow Measurement of Water by the Venturi
          Meter Tube.  ASTM D2458-69.

     4.   American Society for Testing and Materials.   Standard
          Method for Open Channel Flow Measurement of
          Industrial Water and Industrial Wastewater by the
          Parshall Flume.  ASTM D1941-67.
                           198

-------
5.    British Standards Institution.   Methods of
     Measurement of Liquid Flow in Open Channels.
     Standard No. 2680-4A, Part 4A,  1965.

6.    International Standards Organization.   Measurement of
     Water Flow in Closed Conduits—Tracer  Methods,  Part
     I:  General.  ISO No. 2975/1, 1974.

7.    International Standards Organization.   Part II:
     Constant Rate Injection Method  Using  Non-radioactive
     Tracers.  ISO No. 2975/2, 1974.

8.    Hydraulic Institute.  Standards for Centrifugal,
     Rotary and Reciprocating Pumps.  12th edition.

9.    International Standards Organization.   Liquid Flow
     Measurement in Open Channels — Velocity Area
     Methods.  ISO 748, 1976.
                      199

-------
8.0  PUMP CONTROL METHODS


     8.1  VARIABLE FLOW SERVIC3

          A.   Introduction

               This section explains some ways pumps are used to control
               wastewater treatment flows.  Where pertinent to control,
               principles of pump operation are included.  Subjects such  as
               sizing, mechanical details, and manufacturer's options  are
               not included in this discussion.  For further information  on
               these subjects, see the references listed at the end of  the
               section.

               Three classes of pumps are presented here:" metering,
               positive displacement, and centrifugal.  Although metering
               pumps use the positive displacement principles, they are
               considered separately because they form a major subgroup of
              ^positive displacement pumps.

          B.   Metering Pumps

               1.   Applications

                    In wastewater treatment plants, metering pumps are  used
                    to add polymer or other chemicals to clarifiers for aid
                    in settling or for precipitation of pollutants, to  add
                    chemicals to boiler makeup water, to add chemicals  for
                    dewatering of sludges, to add acid or base for pH
                    control, and in other similar ways.

                    In an open-loop control system, the pump is usually
                    either adjusted manually to tne desired rate of addition
                    or paced to the main process flow.  Manual adjustments
                    are recommended only for processes that operate at  a
                    constant or nearly constant flow.  When addition  is
                    paced to the process flow, the addition rate is
                    calculated as follows:
                    where:

                    D   »  dosage, mg/1
                    Q   »  main process  flow, 1/min
                    QA  »  chemical addition  rate, I/rain
                    p   «  density of chemical, g/1
                                   200

-------
?or variable stroke pumps,  the  stroxe  length is:

     L  =  D  •   Q
             SAL

where:

S  =  pump speed, stroKes/min
A  =  piston area, cm2
L  =  stroke length, cm

And for variable speed pumps,  the  speed  is:

     S  -  D  •   Q
             LAP

Typically, the flow signal  and  the  pump  control  signal
are both 4-20 ma, and the dosage  is set  at  an electronic
ratio station.  If both  speed  and  stroke are variable,
the practice is to pace  pump speed  and manually  adjust
stroke to set the dosage, thus  eliminating  the ratio
station.  In open-loop applications, errors  in stroke
and speed accuracy are not  compensated by controller
action.

Accuracy of stroke adjustment  is  typically  stated  to be
+1% of full capacity, with  linearity and repeatability
'also ±1%.  In terms of absolute error, stroke adjustment
at constant discharge pressure would perform as  follows:

                         Stroke             Pump  Speed
% Full Strone       Absolute Error        Absolute  Error

   100%                +1%                    0%
    50%                +2%                   +1%
    25%                +4%                   Tl%
    10%                +10%                  +1%

Error is also introduced by a change in  motor speed
resulting from a change  in load.  Another 4-1% absolute
error is added to the stroke error  for 50% stroke  and
less.  During the life of a pump, error  will increase
due to wear on moving parts that allow hydraulic leaks
and metered liquid leaks. . Another  source of error is
entrainment or buildup of gas  that  causes some piston
displacement to be negated by compressibility of the
gas.   Mass flow rates will be affected by changes  in
metered liquid density (e.g., due to temperature
changes).
              201

-------
             Closed-loop systems involve a process measurement
             downstream of the chemical addition point.  A  controller
             uses this measurament to vary the metering  rate  to  match
             the process aetpoint.  Errors in speed or stroke
             adjustment are corrected oy the controller.  In
             closed-loop applications the process requirements for
             turndown of chemical addition can influence the  choice
             of variable drive.  Variaole stroke pumps can  turndown
             100% to 0% of rated pump output, although strone
             accuracy would normally limit turndown to 10:1.

             Variable speed pumps on the other hand,  are typically
             limited by the type of drive from 3:1 turndowns  to  about
             10:1 turndowns.  Examples of open-looo and  closed-loop
             applications are shown in Figure 8.1.
    PRESSURE
                       ROTARY
                        PUMPS
RECIPROCATING
   PUMPS
                                                 FLAT
                                                   STEADY
                                                    RISE
                             STEEP
                              RISE
                              FLOW
Figure 8.1.   Typical centrifugal pump curves, at constant  speed.
                            202

-------
                     2.    principle of Operation

                          Metering pumps are positive  displacement type pumps of
                          either the reciprocating or  rotary  type.  Reciprocating
                          metering pumps have two general  methods to vary pump
                          output:  variable speed or variable stroke.  Stroke on a
                          variable speed pump is adjusted  by  either varying the
                          crank travel directly  (amplitude modulation)  or by
                          varying the amount of fixed-crank travel transmitted to
                          the piston.

                          Amplitude modulation can also  be achieved by using a
                          slider-crank in which the length of a pivot arm (or
                          eccentric)  is adjusted.  Adjusting  the pivot arm to zero
                          length results in zero piston  travel.  Design of
                          slider-crank mechanisms vary by  manufacturer.  (An
                          example is shown in Figure 8.2.)

                          Another method to modulate amplitude is by the
                          shift-ring drive in which the  piston rotates in a ring
                          that can be positioned.
    HIGH
    SPEED
    WORM
                  ROTATING
                  CRANK
           PLUNGER
           DRIVER
                                             CONNECTING  ROD
WORM?
GEAR
                     ZERO STROKE
                                                              FULL STROKE
    ADJUSTABLE
       LINK 	
CONNECTING
   ROD
PLUNGER
DRIVER
                  ZERO  STROKE
                                                  WORM
                                                  GEAR
                                                               FULL  STROKE
                      Figure  8.2.   Slider-crank stroke adjustment.
                                        203

-------
         Fixed-crank strode adjustments use a lost-motion drive
         that limits the  piston or diaphragm travel.   Motion can
         be lost in the  transfer from crank to piston as shown in
         Figure 3.3.
      STROKE
    ADJUSTMENT
       KNOB
                      RECIPROCATING
                        PLUNGER
               ECCENTRIC CAM
                                      MECHANICALLY
                                      ACTUATED
                                      DIAPHRAGM
                                                       SUCTION


            MECHANICAL LOST-MOTION DRIVE  CHANGES THE DISCHARGE
            FLOWRATE BY VARYING THE PLUNGER RETURN POSITION.
            CRANK ECCENTRICITY REMAINS CONSTANT OVER THE ENTIRE
            FLOW RANGE.
Figure 8.3   Sccentric cam  lost-motion stroke adjustment.
         The piston reciprocates as  it  follows the eccentric cam
         until  the  piston is stopped by the  stroxe adjustment
         pin.   piston travel is resumed when the eccentric
         rotates  enough to pass the  position of the piston  stop.

         Another  lost-motion drive is shown  in Figure 8.3."  Here
         motion is  lost between the  piston and the diaphragm by
         allowing some of the hydraulic fluid to escape to  a
         reservoir.
                        204

-------
                  CONTROL
                  PLUNGER
1?0TOLOL              "^CHARGE
          DIAPHRAGM     4
         ECCENTRIC
           DRIVE
          A PORTION OF HYDRAULIC FLUID IS  PERMITTED  TO  ESCAPE
          THROUGH A BYPASS  VALVE  WITH EACH STROKE, THEREBY
          CHANGING  THE EFFECTIVE  STROKE-LENGTH OF THE PLUNGER.
          NOTE THE BALANCED-DIAPHRAGM LIQUID END ASSOCIATED
          WITH THIS DESIGN
Figure 8.4.  Hydraulic  lost-motion stroke adjustment.

       Variable speed drives on a metering  pump can be
       eddy-current, Silicon Controlled  Rectifier (SCS),
       variable frequency, or belt drives  using conical pulleys
       to vary the ratio of drive to  pump  speed,  variable
       speed drives are explained in  Section 9.

       Metering pumps can have just variable speed, just
       variable stroke, or both variable speed and stroke
       capabilities.  The choice of variable drive depends on
       the pump's application.

       Another method of metering uses a recycle valve to vary
       pump output.  Variable rate pumps are more common
       because in automatic control situations they can
       eliminate the cost and maintenance  of a control valve.
       The variable rate pumps also provide energy savings.
                      205

-------
C.   Positive Displacement pumps

     Positive displacement pumps (p.d. pumps) used in wastewatec
     treatment are usually diaphragm, piston, or progressive
     cavity types.  These pumps are used to pump liquids with high
     solids content such as thickened sludges.

     Diaphragm and piston pump are large scale versions of  the
     metering pumps discussed above.  Variable speed and variable
     stroke control capabilities also apply here,  progressive
     cavity pumps do not have variable stroke capability; the
     rotor and stator are not adjustable.

     Control methods for positive displacement pumps are either
     open-loop or closed-loop.  A typical open-loop system  is
     sludge withdrawal from a clarifier or thickener.  Constant
     rate p.d. pumps are controlled by a frequency and duration of
     opertion basis (i.e., open-loop).  Frequency and duration are
     adjusted to give a desired average flow rate as follows:

               Q  =  fxdxSxV

          where:

          Q  =  pumped flow, 1/min
          f  »  frequency, starts/rain
          d  =  duration of pumping, min/start
          S  =  pump speed, strokes/min
          V  =  stroke volume, I/stroke

     Frequency needs to be often enough to scour sludge lines of
     sludge that may have settled out while the pump was off.
     Duration needs to be short enough to prevent short circuit or
     vortex formation through, the sludge blanket.  Frequency and
     duration should not be so often and short as to cause
     excessive wear and overheating on the motor starter and
     windings.

     Alterations to this control strategy include:

     •    Set frequency in terms of volume of clarifier influent
          flow.  This needs a clarifier influent flow meter.

     •    Stop pump based on duration or low-density cutoff,
          whichever occurs first.  This needs a suspended solids
          analyzer.

     •    Start pump at high blanket level and stop at low  blanket
          level.  This requires two blanket level detectors.

i     •    A ccmbintion of any of the above options.
                        206

-------
     A variacle rate pump can be operated witii the same control
     metiiod,-but augmented to ta!
-------
However, just because a pump  has  a  curve that meets the
processes requirements at  nigh  efficiency,  dees not mean it
is the best pump for the application.   The  designer must also
consider average and maximum  horsepower (braise-horsepower)
requirements, net positive suction  head, impeller design,
number of stages, volute design,  diffuser  design, and
mountings.  These topics are  beyond the scope of this
section, but are presented in the referenced literature.
                                           PUMP
                                        EFFICIENCY
                                          CURVE
         p,	
  PRESSURE
         P,,	
                       SYSTEM
                     HEAD LOSS
                       CURVES
                                                        EFFI-
                                                        CIENCY
                                FLOW
Figure 8.5.  Sizing curves foe centrifugal pumps.

The  most common flow control method for centrifugal pumps  is
with a throttling valve.  In design selection, a portion of
the  pump head at maximum flow is used for loss at the
throttling valve.  This portion may range from as low as 20%
up to 33%.  It is set by desired throttling valve gain
characteristics, desired safety factors,  and energy
conservation.
                    208

-------
          For  small process flows, the portion is often toward  the
          higher  percentage because energy conservation is not  as
          important as gain and safety factors.  The opposite is true
          for  large process flows.  Here, lower percentages, are favored
          oecause of lower energy costs.  Thus, pump sizing is  strongly
          affected by the valve size.  This js discussed in more detail
          in the  section on control valves.

          The  output of a centrifugal pump is also controlled with  a
          recycle valve.  In this case, valve sizing and valve  headloss
          do not  affect pump sizing.  To allow total recycle, all the
          pump head is lost or dissipated at the valve.

          Pump output can also be changed by varying pump speed.  A
          variable speed drive, such as variaole frequencv drive, eddy
          current, or SCR drive, is used to control gump speed.  These
          and  other variable speed drives are explained in the
          Section 3.  These drives have less energy requirements than
          control valves.  Due to inefficiencies of a drive, energy
          savings do not occur until average pump operation is  under a
          certain percentage of pump speed.  Several sources estimate
          this break-even point to be about 80-90% of full speed.   A
          comparison of variaole speed drives with throttling valves is
          shown in Figure 8.6.
         PRESSURE
 ^-    PUMP WITH
Jf  THROTTLING VALVE
                                                         SYSTEM
                                                          CURVE
                               V/S PUMP «    • I-
                               MORE  EFFICIENT |
                                             I
                              	L
                C/S PUMP WITH
                VALVE MORE
                EFFICIENT
                                             as
                                             Q
                                             AVE
                IOO
                Q
                                                     MAX
                                       FLOW
Figure 8.6.  Variable speed versus  throttling of centrifugal pumps.


                             209

-------
         These control methods also apply to multi-pump  systems,   in
         addition, starting and stopping pumps  is a way  to  alter  trie
         output of a pump station.  When more than one pump is  in
         operation, station output can be calculated  from the curves
         of the individual pumps.  In general,  pumps  in  parallel  need
         similar curves and will have their capacities added together
         which produces a longer, flatter curve,  pumps  in  series will
         have their heads added together which  results in a higher,
         steeper curve.

         For example, consider a two pump system, with identical  pumps
         in parallel.  The pump station output  is controlled by a
         throttling valve.  A flow meter on the station  discharge is
         used to shut off one of the pumps when flow  falls  below  80%
         of one pump's capacity and start a pump when flow  rises  above
         100% of one pump's capacity.  The system is  shown  on Figure
         8.7.  In  this example, head losses at  the' throttling valve
         are a substantial portion of the pump  curve.  Could the  use
         of variable speed pumps save energy somewhere below 100% of
         station output?
    PRESSURE
                                                  100
                                  FLOW.% 0
                                         MAX
Figure 8.7.  Two identical pumps  in parallel with throttling valve.
                             210

-------
      Now look  at  the  sane  pump  curves  wnere the pumps are variable
      speed.  Assume that pump turndown is limited to 70% of
      maximum speed by the  construction of the variable speed
      drive.  Speed is related to  pump  performance approximately as
      follows:
      Flow capacity
      Head
      Speed    x  Maximum capacity
    Max Speed

      Speed  2  x  Head at maximum  speed
    Max Speed
      Horsepower     =     Speed   3  x  Horsepower at maximum speed
                        Max Speed

      Therefore, the turndown  limit  on  capacity is from 100% to 70%
      of maximum capacity.   This  system is shown in Figure 8.8.
      Using  just variable  speed and  start/stop control is not
      enough  to provide a  continuous range of control from one pump
      at minimum speed to  two  pumps  at  maximum speed.  A control
      gap occurs from 50-70% of maximum station output.  Either a
      recycle valve or throttling valve is needed to eliminate this
      gap.  Energy savings  should be expected if the average flow
      is less than about 80-90% of maximum.
      PRESSURE
                            TWO PUMPS.MAX
                                      REGION
                                      OF NO
                                      FLOW
                                      CONTROL
REGION OF
NO FLOW
CONTROL
                              35
                                    5O      7O

                                   FLOW. X MAX
                                     IOO
Figure 8.8.  Two identical variable speed  pumps  in parallel.
                          211

-------
     When used for controlling wet well level in raw plant
     influent, centrifugal pumps are normally constant speed;
     started and stopped at selected level trip points.  Usually
     tight level control is not needed, and flow is allowed to
     swing between wide limits.  Once inside the plant, level
     control is often more stringent, and variable rate pump
     stations are more common.

E.   References

     1.   Poynton, James, p.  "Basics of Reciprocating Metering
          Pumps."  Chemical Engineering, May 21, 1979, p. 156.

     2.   Bristol, John M.  "Diaphragm Metering Pumps."  Chemical
          Engineering, September 21, 1981, p. 124.

     3.   Coughlin, John L.  "Control Valves and Pumps:  partners
          in Control."  Instruments and Control Systems, January,
          1983, p. 41.

     4.   Hilsdon, Charles W.  "Using Pump Curves and Valving
          Techniques for Efficient Pumping."  Research and
          Technology, March, 1982, p. 157.

     5.   "Energy Evaluation in Centrifugal pump Selection."
          Plant Engineering, April 5, 1979, p. 71.

     6.   DeSantis, G. J.  "How to Select a Centrifugal Pump."
          Chemical Engineering, November 22, 1976, p. 163.

     7.   Burris, Bruce E.  "Energy Conservation for Existing
          Wastewater Treatment Plants."  Journal WPCF, Volume 53,
          No. 5, May, 1981, p. 537.

     8.   Yedidiah, S.  "Make pumps with Drooping Curves Your
          Servants, Not Your Enemies."  Power, March, 1982, p. 51.

     9.   Zell, Blair.  "Pumps and Pumping Systems:  Specifying  to
          Save Energy."  Specifying Engineer, October,  1981, p.
          117.
                         212

-------
9.0  VARIABLE SPEED DRIVE


     9.1  MAGNETIC COUPLING

          A.    Application
               Variable speed drives  are used for  pumping or  other
               mechanical functions  that cannot be properly accomplished
               with a reasonable number  of  constant speed units.   Variable
               speed drives also offer increased flexibility in  control.

               A magnetic coupling variable speed  drive system uses a
               standard constant speed induction motor to drive  a coupling
               (clutch) that has an  adjustable output  speed.   This  drive
               offers good flexibility,  with such  options as braking, and
               accurate speed control by a  feedback signal produced by a
               tachometer generator  on the  output  shaft.

               Characteristics of a  magnetic coupling  variable speed drive
               are:

               1.   Uses standard constant  speed AC squirrel  cage induction
                    motor.

               2.   Generally for treatment plant  applications a wide range
                    of 10 - 750 KW (15 - 1,000 Hp) is  available.

               3.   Minimum cost, simple variable  speed drive.

               4.   Suitable for variable torque pumping or fan  loads.  Not
                    suitable for conveyors  and piston  pumps that are subject
                    to heavy vibrations.

               5.   Low efficiency at reduced speeds.   At low speed a large
                    amount of power  is dissipated  as heat in the magnetic
                    coupling.  This  requires cooling the magnetic coupling
                    by air or liquid.

                    Don't use magnetic couplings at speeds below 75% of
                    nominal speed for an extended  time because of lowered
                    efficiency.

               6,   Water cooling to  improve heat  dissipation is generally
                    required above 300 KW (400 HP).

               7.   Magnetic coupling reliability  is good, and minimal
                    maintenance is normally required.   It has brushes, but
                    unlike dc motors  and wound rotor motors,  they are on the
                    magnetic coupling and carry only small currents.
                                    213

-------
     8.   Potential proalems exist in maintaining proper alignment:
          between the motor, magnetic coupling, and pumps.

     9.   Additional floor space (for horizontal drives) or
          additional ceiling height (for vertical drives) is
          required, as compared to most other variable speed
          drives.

B.   Principle of Operation

     Magnetic coupling variable speed drives use a constant speed
     induction motor to drive a ferrous metal ring that rotates
     around a dc excited magnetic rotor connected to the load.  DC
     current in the magnetic rotor is increased or decreased to
     vary the degree of coupling force generated.  Output speed of
     the drive is a function of the strength of "the rotor magnetic
     field and the load on the output shaft.  Output speed is
     automatically controlled by a speed controller that compares
     the output speed signal from the speed transmitter to a
     setpoint and adjusts the amount of dc current to the magnetic
     rotor to maintain the desired speed.  See Figure 9.1.
                                                     CONTENT SPEED
                                                          MAGNETIC
                                                          COUPLING
               !      L
               1	SPEED FEEDBACK. _
      Figure 9.1.  11a£net±c coupling functional block diagram.
                             214

-------
C.    Speed Controllability

     Remote speed control by a signal from an external source is
     available.   See Figure 9.2,

     Controllability is good, and accurate speed control can be
     obtained.
                           215

-------
                                              *;—0^j_
                                                           MOTOR STARTER
             MS AUX
          a—i  H—a
                        TO VARIABLE

Cf















•u 3










_J

ft


) UOC



L








ISAUX


AL
a
DttSlta OEC^TE2)

.— ^ 1 r< ^•oJ_Q— j

0|NC souo STOTE G) OECa
RAMP OENERATOR a
Sjf. I «-20 MA OU
1 | 	 	 TO v*ai*ai
1 ' CONTROU.C
® ®
START C»Z
©
STOP
®
START
STOP


                                          €>
             SP€£0    (3)
           TMANSMITTtR
                                                                     START MOTOR
                                                           STOP MOTOR
                                                           MOTOR SUNNING
® LOCATED AT PUMP/MOTOR

® LOCATED AT MCC       ^ (4.jo MA)

® LOCATED AT LOCAL PANEL

® LOCATED AT COMPUTER INTERMCC

® LOCATED AT VARIAM.E SPEED CONTROLLER

12 COMPUTER INTERFACE TERMINALS
                                     SPEED    ©
                                    INDICATOR
                                        NOTE(S)
                                          11 SAFETY LOCKOUTS ANO/OR UNIQUE CONTROL
                                           FUNCTION INTERLOCKS FOR THE PARTICULAR
                                           APPLICATION
                                          2) COMPUTES OUTPUT CONTACTS  ARE
                                           MAINTAINED  CLOSED  OUR I NO CONTROL
Mgure  9.^.   Magnetic  coupling variable  speed pump.
                           216

-------
9.2  LIQUID RHEOSTAT

     A.    Application
          Variable speed drives  are used  for  pumping  or  other
          mechanical functions  that cannot be properly accomplished
          with a reasonable number  of constant speed  units.   Variable
          speed drives offer increased flexibility in control.
          Improved system efficiency can  also be obtained where
          periodic changes in the demand  allows reduced  horsepower,
          consequently,  offering an energy savings.

          A liquid rheostat variable speed drive system  uses  a  wound
          rotor motor.  The motor speed is adjusted by changing the
          rotor current as determined by  the  depth in which  the
          rheostat plates are submerged in liquid.

          Characteristics of a  liquid rheostat variable  speed drive are:

          1.   Uses wound rotor  motor.

          2.   'Available in all  standard  motor sizes  from 10 -  750 + KW
               (15 - 1,000 HP).

          3.   Not suitable for  constant  torque loads.  A reasonably
               good drive for variable torque pumping and fan loads.

          4,   In general, a 2  to 1 speed range is available.

          5.   Overall efficiencies range from about  85% at  full speed
               down to approximately 45%  at half speed.

          6,   The power factor  is  poor at low speed.

          7.   A heat exchanger, with circulating pump,  is required to
             .  dissipate from the liquid  in the rheostat the heat
               produced by the  electrical slip in the motor  used to
               obtain variable  speed operation.

          8.   Maximum speed, with  minimum resistance between plates of
               the liquid rheostat, is about 95% of full speed.

          9,   Motor starting current can be reduced  to  less than
               full-load current by having maximum resistance between
               plates of the liquid rheostat during startup.

          10.  Problems with brushes and  slip rings on the wound rotor
               motor occur with  moderate  frequency.
                                217

-------
3.   Principle of Operation

     Electrical resistance between  the  liquid  rheostat plates
     determines the wound rotor  motor current  which regulates the
     motor speed.  The motor speed  is adjusted by a change in the
     depth of the liquid in which  the rheostat plates are
     submerged.  See Figure 9.3.
          PNEUMATIC
           SPEED
           SIGNAL
                        ELECTROLYTE
                          PIPING
      Figure  9.3.  Liquid rheostat functional block diagram.

                           218

-------
C,    Speed Controllability

     Remote speed control by a  signal  from an  external  source is
     available.   See Figure 9.4.

     Controllability is  generally good,  but accurate  speed control
     is  difficult to obtain due to the slow response  inherent with
     the pneumatic interaction  required  to change  the submergence
     of  the rheostat plates in  the liquid.
                          219

-------


(—— — — _,
©

»
1ST
r




T 	 1

                                                  ©
                                                \-~/
                       I4.M M4,
(3)
0
UOCATCO AT PUMP/ MOTOR
UOC4T10 AT MCC
UOCATCO Ar LOCAI. PUKL
UOCATIO AT COMPUTER INTERFACE
UOCATEO AT VAMAILC 3PCEO CONTROLLER
COMPUTER INTERFACE TERMINALS
                                                 <^
                                                                  START MOT5*
                                                                 MOTOR HUNNMi
                                               NOTEIS)
                                                II SAFETY LOCKOUTS ANO/OR UNIOUE =
                                                  FUNCTION INTERLOCKS TOR THE ?*-~
                                                  APPL1CATION
       Figure 9.4.    Liquid  reheostat  variable speed  pump.
                                      220

-------
9.3  VARIABLE FREQUENCY

     A.    Application
          Variable speed drives  are used for  pumping or other
          mechanical functions that cannot be properly accomplished
          with a reasonable number of constant speed units.   Variable
          speed drives offer increased flexibility in control.
          Improved system efficiency can also be obtained where
          periodic changes in the demand allow reduced horsepower,
          consequently, offering an energy savings.

          A variable frequency drive (VFD) system consists of an
          induction motor where  both the voltage and frequency supply
          controlled by an electrical inverter to adjust the motor's
          speed.

          VFD's are available for a wide range of standard motor sizes.

          Characteristics of a VFD system are:

          1.   Other than the addition of thermostats in two phases of
               the stator winding, a standard squirrel cage ac
               induction motor can be used.

          2.   All standard motor sizes available from 4 - 400 KW (5 -
               500 HP).

          3.   Suitable for variable torque pumping or fan loads.
               Normally suitable for piston pumps and conveyors.

          4.   Continuous operation at constant torque is available
               over a  3 to 1 speed range.

          5.   Overall efficiencies are about 83% at full speed down to
               approximately 75% at half speed.

          6.   Multiple motors can operate off one common VFD
               simultaneously.  Also, one VFD can control more than one
               motor where it is switched between motors to give a
               combination fixed speed and variable speed system.

          7.   The VPD can convert existing constant speed motors to
               variable speed operation when retrofitting existing
               installations.

          8.   Starting current can be limited to less than full-load
               current.

          9.   Requires little maintenance; however, complex components
               and circuitry require an expert technician when problems
               do occur.
                                221

-------
Principle of Operation

The variable speed controller/power converter changes
constant frequency, constant voltage line power to variable
frequency, variable voltage power to vary the drive motor's
speed.   Raising the frequency of the power applied to  the
drive motor increases its speed.  Lowering the frequency
decreases its speed.  Voltage applied to the drive motor  is
adjusted to control the motor's output power.  The variable
speed controller compares the drive motor's speed to an
adjustable setpoint value and outputs the required frequency
and voltage to maintain the desired speed.  See Figure 9.5.

Speed Controllability

Remote speed control by a signal from an external source  is
available and is probably the most advanced" speed control
method available today.  See Figure 9.6.  Controllability  is
excellent, and accurate speed control can be maintained.
                                                    AC
                                                   POWER
PUMP  ) C PUMP  )    C PUMP ) CPUMP j C PUMP
                 >
           PUMP

         L-SIMPLEX-1
           UNIT
  Figure  9.5.   Variable  frequency drive functional diagram.
                       222

-------
                                                                          CONSTANT
                                                                          SPEED
                                                                          MOTOR
                                                                          STARTER

                              • I2O VAC  SO HZ •
                             STlRT
                        HS—i r—3
                             STOP
                      i—a—i MS
                  0-4-
u 	 • 	
a
y
®
START
i



_J 	
Kl 	 '



   ©LOfLATFQ AT PimP
   LOCATEO AT PUMF

   ©LOCATED AT MCC
   LOCATED AT MCC

© LOCATED AT LOCAL  PANEL
W
0 LOCATED AT COMPUTER INTERFACE

© LOCATED AT VFO PANEL

^ COMPUTER  INTERFACE TERMINALS
NOT El SI
 |( S4FETT LOCKOUTS 4NO/OR UH.QUJ
   FUNCTION  NTERLOCXS FOR TH£
   PARTICULAR APPLICATION
 *l INCREMENTAL SETPOINT CONTROL
   SOLID STATE RAMP OENeRATOR,
   MOTORIZED POT.OR EOUIVALEMf
                                                                          MOTOR  REOL-a
                                                                          ON VARIABLE Sa
                                                                         MOTOR RUNMXS
                                                                        I AT CONSTANT 5=
           Figure  9.6.    Simplex  VFD  variable  speed pump.
                                           223

-------
9.4  VARIABLE  PULLEY

     A.    Application

          Variable speed drives  are used for  pumping or other
          mechanical functions  that cannot be properly accomplished
          with a reasonable number  of  constant speed units.   Variable
          speed drives also offer increased flexibility in control.

          Electromechanical variable speed pulley belt drives  use a
          variable sheave ratio  principle to  change the speed  of the
          final element.

          Characteristics of a  variable pulley variable speed  drive are:

          1.    Available in all  standard motor sizes from 0.2  - 75 KW
               (1/4 -100 HP),  but are normally used only in the lower
               ratings of 0.4 -  20 KW (1/2 -  25 HP).

          2.    This is a constant torque drive.

          3.    In general, a 10  to 1 speed range is available.

          4.    Overall efficiencies are about 70% at maximum speed down
               to approximately 45% at half speed.

          5.    Additional floor  space or ceiling height is required as
               compared to most  other drives.

          6.    Belt life is typically 18 months.

     B.    Principle of Operation

          Variable pulley or electromechanical drives use a constant
          speed motor coupled to a variable belt drive system for speed
          control.  Output speed is varied by changing the diameter of
          the drive sheave or pulley.   Drive sheave diameter is
          adjusted using a reversing gear motor connected mechanically
          to the drive system.   When the gear motor operates in one
          direction, the sheave diameter is increased and the drive
          speed increases.  When the gear motor operates in the other
          direction, the sheave diameter decreases and the drive speed
          decreases.
                                224

-------
C.    Speed Controllability

     Remote speed control by a signal from an external source is
     available.   See Figure 9.7.

     Potential operational problems holding a speed setting can be
     numerous due to belt wear, belt stretching, and groove-worn
     pulleys.  Small stepless speed adjustments are difficult co
     obtain (and maintain).
                          225

-------
                               I2O VAC SO HZ
                               I2O VAC SO HZ
                                    -C	B
                                    -r     _
                                     '—a
           LOCAL   CPU
                ®
     MS

     AUX
     ®
                         SM
                             © START
                             ©  STOP

                              1—SJ-
                         STOP      ®
0   INC
                       -BH
                          ®_i
                          ®_
                             ©
                             MS
                             AUX
                            \®
                                               CR4     LS
— SI —
DEC
TX
--I2S
~'NC
~OK


	 is: 	 isr- 	 -\
® ®
CR3 LS
rs* i "** i
/^ro»
                                           START

                                           MOTOR
                                           STOP

                                           MOTOR
                                                                        INCREASE

                                                                        SPEED
                                                                            TOMOTOS

                                                                            CONTROL

                                                                            CIRCUITS
                                                                       > MOTOR RUNMNS
Q LOCATED AT PUMP/MOTOR


(|) LOCATED AT MCC


(j) LOCATED AT LOCAL PANEL


0 LOCATED AT COMPUTER NTERRCE


(3) LOCATED AT VARIABLE SPEED   (4"20

  CONTROLLER


^ CCNVUTER INTERFACE  TERMINALS
                         NOTE (SI'

                           I) SAFETY LOCKOUTS */O« UNIQUE

                            CONTROL FUNCTION INTERLOCKS AS

                            PER THE PARTICULAR APPLICATION.
        Figure 9.7.   Variable pulley  drive control  circuit.
                                           226

-------
9.5  DIRECT CURRENT SILICON CONTROLLED "ECTIFIEH (SCI)

     A.    Application

          Variable speed drives are used for pumping or other
          mechanical functions that cannot be properly accomplished
          with a reasonable number of constant speed units.   Variable
          speed drives offer increased flexibility in control.
          Improved system efficiency can also be obtained where
          periodic changes in the demand allows reduced horsepower,
          consequently, offering an energy savings.

          Variable speed control of dc motors is achieved by varying
          the armature or field voltage to the motor, or both.

          Characteristics of dc variable speed drives are:

          1.   DC motors are considerably more expensive than
               comparable ac motors.

          2.   In general, for treatment plant applications, drives are
               available from 4 - 100 KW (5 -150 HP).

          3.   Can be used for variable torque operation.  Usually
               suitable for piston pumps and conveyors.

          4.   In general, a speed range of 60 to 100% is available.

          5.   Reduced speed efficiency is very good.

          6.   The dc motor has a commutator and brushes, both
               potential maintenance problems,

          7.   Commutators on dc motors can cause problems if they are
               not well ventilated and properly maintained or if they
               are subject to a corrosive environment.

          8.   Drive requires little maintenance; however, complex
               components and circuitry require an expert technician
               when problems do occur.

          9.   Starting current can be limited to less than  full-load
               current.

     B.    Principle of Operation

          The term SCR drives is defined as variable speed drives that
          are based on the use of a dc motor.  3CR drives include a
          speed controller that uses an SCR controlled bridge circuit
          to rectify constant voltage ac line power to variable voltage
          dc power.  Variable voltage dc power is applied to the dc
          motor to regulate its speed.  As the applied voltage
          increases, the motor speed increases as the voltage
          decreases, the speed decreases,  SCR speed controllers accept
          an input signal representative of the desired motor speed and
          provide a dc output sufficient to operate the motor at the
          required speed.

                                227

-------
C.   Speed Controllability

     Remote speed control by a signal from an external source is
     available.  See Figure 9.8.

     Controllability is good, and accurate speed control can be
     maintained.
                           228

-------

c
Id
BiJ— i













•u d
x










__j



) L0<
]
'J~
1


_










:AL
*•
I — £




d



I



_
7t
LI
INC;NOTED
\& M 123 • Efl
INC OE
_L© _J
3 1 NX i
	 , I rXX. |

INC SOLID STATE
RAMP SENERATC
 I
rffi !.. _

©
START
STOP
®
START
STOP




®
XC. (NOTED
1 | ,<^
! I £y
s
-*-!

Q DEC a
in a
4-20 MA OU
TO VARIABL
CONTROU.E
®
CR2
-vj




                                        ®
                                                         START MOTCil
(T) LOCATED AT PUMP/MOTOR

(2) LOCATED AT MCC        ~(4-ZOMA)

(?) LOCATED AT LOCAL PANEL

0 LOCATED AT COMPUTER INTERFACE

® LOCATED AT VARIABLE SPEED CONTROLLER

12 COMPUTER NTERFACE TERMINALS
                                       I) COMPUTER OUTPUT CONTACTS ARE
                                        MAINTAINED CLOSED DURING CONT93..
Figure 9.8.   DC variable  speed  drive.
                         229

-------
10.0 CONTROL VALVES


     10.1 MODULATING SERVICE

          A.   Application
               Control valves for modulating service are used in all
               wastewater treatment processes.  Excluded from this
               discussion are valves used in isolation or routing service in
               two states; open or closed.  Commonly used control valves are
               compared in Table 10.1.  Their applications are presented
               later in the text and in Tsl^e 10.2.
           TABLE 10.1.  COMPARISON OF CONTROL VALVES  IN WASTEWATER
                             TREATMENT PROCESSES
     Valve Type

     Ball (Rotary)
     Butterfly
     (Rotary)
     Gate (Linear)
     Globe (Linear)
     Eccentric plug
     (Rotary)
High pressure recovery
Tight shutoff
Equal percentage flow
  characteristic
Available with flangeless
  connection
1-24 inch sizes

High pressure recovery
Equal percentage flow
  character is tic
Good shutoff
Usually a flangeless connection
2-144 inch sizes
                                     Cost
Low cost
Lowest cost
Low pressure recovery
Choice of flow characteristics
Good shutoff
Usually small size applications
1/2 - 16 inch sizes

Equal percentage and linear
  flow characteristics available
Good shutoff
Moderate pressure recovery
2-24 inch sizes
Not usually
used for
modulating
service

High cost
Moderate cost
                                 230

-------
BALL VALVE





  Figure  10.1.   Ball valve.
          231

-------
B.   Principle of Operation

     Control valves  (modulating  service  is  implied  in  this  term)
     are made in a wide variety  of designs.  Five designs used in
     wastewater control applications  are presented  here.  There
     are many, many  other designs, but this  discussion will make
     you aware of some of the problems encountered  in  control
     valves.

     1.   Ball valves.

          Valves are classified  as either  "rotary"  or  "linear."
          In a rotary valve, the ball, disk, or  plug is rotated to
          open or close the  flow stream. A  linear  valve  lifts the
          gate, disk or plug up  or down  to open  or  close  the flow
          stream.  Ball valves are rotary.   Flow goes  through a
          port in the ball.  To  shut  off flow, the  ball is  rotated
          until the  port is  closed.   The ball  may be a complete
          sphere, full ball, as  shown in Figure  10.1,  or  a  partial
          sphere.  Standard  port diameters  range from  80% of
          inside pipe diameter to 100% or  full port.

          Ball valves have high  friction resistance to rotation
          due to valve body  and  trim  contact with the  ball
          surface.   This gives a tight shutoff at  the  expense of
          needing larger actuators.   In  some designs the  ball is
          allowed to "float" in  its seat so  that line  pressure
          will assist keeping a  tight shutoff  by pushing  the ball
          against the downstream seal ring.  This freedom of
          movement introduces a  deadband between the actuator and
          the ball.  The deadband will make  this design unusable
          for many control applications.  For  control  valves, a
          rigid call to actuator connection  is preferred.
                        232

-------
   2.   Butterfly.

        Butterfly valves  are  rotary  type valves that use an
        axially pivoted disk  to  restrict or  open the flow
        stream.  The disK may be flat or contoured in shape and
        mounted to the atem  (pivot)  in several ways.  An example
        is profiled in Figure 10.2.
                                            DISK
                                            iASKET
                                 BOLT OR STUD
Figure 10.2.  Butterfly valve, swing-through  type  with
             flangeless pipe connection.

        One problem with butterfly valves  is  obtaining a tight
        shutoff.  The seal must be made  along the  entire inner
        circumference of the valve body.   Upper  and  lower half
        seats must be matched and the  pivot point  must be
        sealed.  Liners and seals used for good  shutoff increase
        the opening and closing torque requirements  of the
        actuator.

        Another problem encountered  in butterfly operation is
        torque applied by the fluid.   During  rotation of the
        disn, torque reaches a maximum at  about  70 degrees (from
        full open).  This is shown in  Figure  10.3.  In some
        applications this pea* may exceed  the opening or closing
        torques.  To overcome this problem, disks  are contoured
        for low torque in the near closed  positions.
                     233

-------
     TORQUE
                                                    BRcAK AWAY
                                                      TORQUE
                                                    CLOSED

                      VALVE POSITION (DEGREES)  "



         Figure 10.3.   Butterfly torque.

3.   Gate.

     Gate valves are  linear  valves in which the gate's disk
     is raised or lowered  past a port by the actuator.  The
     disk is a flat or  wedged-shaped plate.  The valve may
     have one or several ports for flow which can be sealed
     by the plate.  A gate valve is shown in Figure 10.4.  in
     knife-gate valves, plates are made with a sharp edge for
     service with solids bearing streams including dry
     solids.  Gate valves  are  not usually used for modulating
     service.
                   234

-------
    Figure 10.4.  Gate valve, multi-orifice.

4.   Globe.

     Globe valves are linear valves  in which  the  plug moves
     up or down into a port.  Some valves  have  two sets of
     plugs and ports, these are called double ported.  In
     order to reduce stem size and to obtain  better seating
     of the plug on the port, the stem or  plug  is
     mechanically guided.  An example of a globe  valve is
     shown in Figure 10.5.
                    235

-------
           Figure 10.5.  Globe valve.

     Actuator size can also be reduced for double  ported
     valves with balanced flow.  The ports and plugs  are
     aligned such that the flowing stream tends  to close  one
     port and open the other, thus balancing the fluid  forces.
5.   Plug.
     Plug valves ara rotary type valves with  a conical  or
     cylindrical shaped plug wnich has an orifice.  Rotating
     the plug at a right angle to flow causes tight shutoff
     while full flow occurs when the orifice  of the plug  is
     parallel to the flow axis.  A simple plug valve  is shown
                    236

-------
          in Figure 10.6.  In the same figure  is  a  popular version
          of the plug valve, the eccentric  spherical plug or
          "camflex" valve.  Just as a traditional plug valve is
          similar to a traditional ball  valve,  the  eccentric
          spherical plug is similar to the  segmented ball valve.
          Both newer designs provide large  flow for the valv« size
          and high pressure recovery yet have  reduced friction
          through most of the valve travel.
                                            TAPERED
                                              PLUG
                                                         STEM
                                 BODY
         AN ECCENTRIC ROTARY VALVE PLUG
                                           TRADITIONAL PLUG VALVE
                Figure  10.6.  Plug  valves.

C.   Valve Size

     Control valves are  rated by  a  "Cv"  factor which is the amount
     of water at 15°C  (60°F) or any liquid  with a specific
     gravity of 1.0, that goes through a full open valve at a
     pressure differential of 6.89  KPa  (1 psi).  The Cv factor is
     found in the general flow equation  below.
                Cv
 A P
S.G.
     Q    = flow, gpra
     Cv   = valve factor gpm/(psi)  V2
      P   = pressure differential,  psi
     S.G. = specific gravity

     While this flow equation  is  not restricted to English units
     of measure, the Cv values  available for valves in this
     country are only for English units.  To use kpa for pressure
     multiply manufacturer's English Cv values by conversions in
     Table 10.2.
                          237

-------
        TABLE 10.2 Cv CONVERSION FACTORS

Cv x conversion factor  =  flow in units

     1.44               =          1pm
     0.0862             =          m  3/h
     0.00144            =          m  3/ra
     0.0000239          =          m  3/s

The metric conversion factors also convert  to  a  specific
gravity at 4°C.  For most wastewater  treatment processes
tne liquid is water at 5-25°C  (41-77°F) so  the specific
gravity factor will cause less than 0.5% correction  and wi 11
be deleted from further discussion hers.  Additional
correction factors for viscosity and  critical  flow and
compressibility for gas flow may De needed.  These factors
and how to apply them are found in manufacturer ' s
literature.  For a complete explanation of  valve sizing see
the ISA text books referenced at the  end of  this section.
In sizing a valve for wastewater  treatment  processes,
the range of flows is known.  A safety  factor  of  110%  of
maximum flow, or 130% of average  flow is  commonly used in the
sizing calculations.  Another way to add  a.  safety factor is
to make calculations using  100% of maximum  flow,  but
selecting a valve that will do the job  at 90%  of  its rated
capacity  (i.e., 0.9 Cv) .  Once the pressure drop  over  the
valve is determined, the valve size can be  calculated  by
rearranging the above equation.   Traditional sizing  rules for
control valves in pump systems call for 33% of system
pressure loss to be at the  valve. This and other rules of
thumb are shown in Figure 10.7.   The lost energy  is  not
wasted, but is used to reduce flows to  the  control setpoint.
                     238

-------
  FOR APD< 1000 kpo (ISOpsi)
 PUMPS
  FLOW < 750 gpm
  FLOW > 750 gpm
                                       -Apn
                                              •^
AP £ 0.25 APQ a > 100 kpa (ISpsi)
AP > 0.2 APn
 GRAVITY FEED
                                -APD-
                                    -AP-H
                          AP> 0.33AP 8 2 O.I
                                            pa
                                                       pa
                                 -APO-
 COMPRESSORS
                          AP > 0.5 AI  a > o.os pa
Figure  10.7.  Traditional pressure drops for control valves.
                               239

-------
This rule of  thumb  is  not  particularly energy efficient and
should be replaced  for  large  sized  flow streams where the
energy cost is  significant.   Allotting less head loss to the
control valve will  tend to increase the valve size up to full
line size, and  will restrict  the  choice of valves to those
with high capacity  (e.g.,  butterfly or ball).  Reducing head
loss at the valve calls for more  careful design than
otherwise because there is less safety factor.  The risk is
that the valve  will be oversized  for the application.  In a
severe case,  the valve  may have to  operate nearly closed to
achieve the setpoint flow, which  may make satisfactory flow
control impossible.  To help  understand sizing of valves,
lets review two fundamentals:  pressure drop and valve gain
and characteristic.

Pressure differential  or drop across a valve is proportional
to the square of flow.   This  is the same relationship that
occurs in differential pressure flow meters:  orifices and
Venturis.  The  pressure profile across a valve is similar to
an orifice or venturi,  and is shown in Figure 10.8.
Similarly the flow  is  dependent on  the pressure difference
measured from upstream to  the vena  contracta.  Due to the
impracticality  of measuring vena  contracta pressure, control
valve flow equations and sizing principles are established
based on upstream and  downstream  pressures.  The relationship
between vena  contracta and downstream pressure is normally a
constant proportion expressed as:
                 -  pvc)
 where:

A P    =   Difference between upstream and downstream pressures,
         kpa (psi)
 Pj_    =   Upstream pressure, kpa (psi)
 Pvc   =   Pressure at vena contracta, kpa (psi)
 FL    =   Pressure recovery factor, unitless

 This  relationship does not hold during conditions of
 cavitation or  flashing in liquids or at sonic velocities in
 the vena contracta in gases.  In these cases choked or
 partially choked flow occur.  When sizing valves for low head
 loss, choked flow and related phenomena are not likely
 problems except where the vapor pressure of a liquid
 approaches the vena contracta pressure as in hot water for
 example.  See  the reference publications for further
 information.
                     240

-------
                               pvc
             pi
  PRESSURE
  PROFILE
    Pi
                J I
                                           I  I
                                   pvc» PRESSURE AT VENA CONTRACTA
                         FL IS THE PRESSURE RECOVERY FACTOR
   Figure 10.8.  Pressure drop across  a  valve.

The recovery factor,  FL,  is combined with other factors  to
form the Cv numbers  reported in  manufacturer's literature.
Therefore, the pressure  difference of most use in sizing
valves is the permanent  pressure loss, A p.

The second fundamental for  review is valve gain and
characteristic.  Valve gain is defined as the change  in  flow
caused by a change  in valve position and may be dependent on
valve position.  The  way in which valve gain changes  with
valve position falls  into three  basic characteristics:

•    Equal percentage -  equal changes of valve position  cause
     equal percentage changes in flow.
                     241

-------
•    Linear - flow changes  linearly  with valve position.

•    Quick opening - flow changes  rapidly with valve position
     at low valve position,  but  only slightly at higher valve
     positions.  Most of the valve capacity is reached after
     opening just a small amount.

These three characteristics are  shown in Figure 10.9.
       100%
    FLOW
   CAPACITY
                                                   IOO% OPEN
                          VALVE POSITION
 Figure 10.9.  Intrinsic valve characteristics.

When these terms are used  to describe  a valve they are called
intrinsic or inherent flow characteristics.   They represent
the gain dependence on position  in  cases where the total
dynamic head loss of a system occurs at the  valve.  As less
proportion of system head  loss occurs  at the valve,  the flow
characteristic shifts to a relationship called the installed
characteristic.  This shift is shown in Figure 10.10 for
linear and equal percentage valves.  Shift  in gain is shown
in Figure 10.11.

At control valve head losses traditionally  used  for  valve
sizing,  p/ PD  - 0.2 to 0.33, "linear" valves approach
quick open response, and "equal  percentage"  valves approach
linear response.  In cases where head  loss  at the valve is to
be reduced to a minimum, the shift  in  valve  response is even
greater.  When viewing Figures 10.10 and 10.11 Keep in mind
that the ratio of valve head loss to total  dynamic head loss
will not be the same at all flows.  This is  shown in Figure
10.11.  For most of the flow range  a valve  will  be close to
its intrinsic characteristic or  gain,  but near maximum flow
the installed characteristic or  gain will shift.
                     242

-------
            loor.
      FLOW
    CAPACITY
      %CV
                                             IOO%
                         VALVE POSITION
             100%
      FLOW
     CAPACITY
       %cu
                                             IOO%
                          VALVE POSITION
 Figure 10.10.   Valve character is tic  shift witii
decreasing ratio of  valve pressure  loss to system
                 dynamic pressure.
                       243

-------
 G
GAIN
                               EQUAL PERCETAGE
                                   VALVE
                                    IOO%
               VALVE POSITION
 G
GAIN
              AP
             *Apn
0.33
050~
I.OO
              VALVE POSITION
LINEAR
VALVE
                                   100 %
  G
GAIN
               VALVE POSITION
                               QUICK OPENING
                                  VALVE
                                    100%
     Figure 10.11,   Installed  valve  gain.
                        244

-------
        100
         80--
         60--
PRESSURE
         40--
         20--
           0
           I
           I
                   20
  40
       I
                                   60
FLOW   I
       I
                                                      .PUMP
                                                       CURVE
                                                      -DYNAMIC
                                                       SYSTEM
                                                      -LOSSES
                                                       STATIC
                                                       LOSSES
                                           80
                                                   100
                                                         VALVE
                                                       CONDITION
                            — AP —
  Figure  10.12.   Valve pressure drop in a  pumping  system.
                               245

-------
Gain analysis  is further  complicated  by  the  behavior of real
valves which although  they  may  exhibit a general type of
characteristic, the actual  installed  characteristic will
deviate from the ideal.   This is  specially true at the limits
of valve  travel.  Generally, a  valve  will only provide
acceptable control over a range of  performance.  This range
may be expressed as a  ratio of  high to low flows,  high to low
valve position, or high to  low  valve  capacity, Cv.  The last
measure of rangeability is  the  most useful in  selecting a
valve.  Using  the sizing  equation,  rangeability requirements
may be calculated by:
     Rangeability
                     CVL    QL       APH
Where the subscrips H and L  indicate high  and  low  flow rate
conditions.

Putting together all valve gain considerations discussed so
far results in a plot of gain versus valve capacity as shown
in Figure 10.13.  The valve  is a cage-guided,  equal
percentage globe valve with  flow tending to open which is
used to throttle a centrifugal pump.  The  application  called
for two thirds of the total  system dynamic pressure losses  at
maximum flow to occur at the valve.  Therefore, the valve
should be close to its intrinsic characteristic throughout
its operation.  Note that the installed characteristic is
only equal percentage from about 7 to 70%  of valve  capacity.
If the change in characteristic outside of this region of
equal percentage is detrimental to control of  the process,
the rangeability is 70 to 7  or 10 to 1.

The concern for predicting valve gain centers  around
obtaining stable control.  That is, the system should  respond
to'load and setpoint changes with desired  dampening and
response time.  A general rule to follow is that the valve
gain should act opposite to  the process gain to produce as
linear a combination as possible.  For example, consider a
flow control situation where the flow rate is  measured by a
differential pressure element.  This follows the previously
stated principle that flow is proportional to  the square root
of pressure difference.  Therefore its gain increases  with
flow.  A quick opening valve has a gain that decreases with
flow and would be a suitable valve choice.  A  linear valve
could also be used if the system operated  near  the  maximum
flow, in which case the installed linear valve characteristic
would be similar to quick opening.  If the flow transmitter
signal was sent to a square  root extractor  and  then to the
controller, the meter's gain would be constant.  In this
case, select a linear valve  for operation  near  the  intrinsic
characteristic, or select an equal percentage  valve for
operation near the maximum flow.
                     246

-------
        2--
      G
    GAIN
                       EQUAL-PERCENTAGE
                       CHARACTERISTICS
                                                   100
                        VALVE CAPACITY, % cv
Figure 10.13.  Gain of  a single ported globe valve. •

 Table 10.3 contains a recommendation  of  valVe characteristic
 for  several control applications.   If there is doubt about
 how  much installed characteristic  to  allow for, or which
 condition overrides choose equal percentage over linear/ and
 linear  over quick-opening.
                        247

-------
         TABLE  10.3.  VALVE CHARACTERISTIC SELECTION GUIDE
CONTROL APPLICATION
Flow
Level

pressure
     D.
              CONDITIONS OF APPLICATION

              o Linear flow signal
              o Differential pressure
                signal
              o Small flow range, large
                pressure drop changes

              o Most applications

              o Liquid
              o Gas with large pressure
                drop
              o Gas in fast responding
                system
              o Gas in slow responding
                system
VALVE CHARACTERISTIC

Linear
Quick-opening

Equal percentage
Linear

Equal percentage
Equal percentage

Equal percentage

Linear
Manufacturer's Options

1.   Body styles are available as presented above and in a wide
     selection of variations.  Consult manufacturer's
     literature for available valve bodies.

2.   Materials of body construction:

     a.   Iron,

     b.   Carbon steel,

     c.   Stainless steel, and

     d.   Hastelloy.

3.   Materials of trim and plug construction!

     a.   Carbon steel,

     b.   Stainless steel,

     c.   Brass,
                               248

-------
          d.    Copper,

          e.    Monel, and

          f.    Other speciality materials are available.

     4.   Stem packing materials:

          a.    TEE, and

          b.    Graphite at high temperatures.

     5.   Pipe connections:

          a.    Threaded,

          b.    Flanged, and

          c.    Plangeless (wafer).

     6.   Body liner material:

          a.    Teflon,

          b.    Buna-N, and

          c.    Viton.

     7.   Trim:

          Trim is available in many configurations for each valve
          type and varies by manufacturer.

     8.   Bonnet:

          Bonnet designs are also varied according to manufacturer.

E.   References

     1.   "Advances in Water and Wastewater Valves." Consulting
          Engineer, September, 1982, p. 105.

     2.   Boger, Henry W.  "The Effect of Installed Flow
          Characteristic on Control-Valve Gain." ISA Transactions,
          Vol. 3, Ho, 4, 1969, p.  265.

     3.   Ramsey, John R. and Charles D. Fournier.  "Matching Valves
          with Process Requirements." Instrument and Control
          Systems, June 1973, p. 65.

     4.   Hammit, Donn.  "Choosing a Control Valve is Easy."
          Instrument and Control Systems, December 1976, p. 28.
                         249

-------
5.   Moore, Ralph W.   "Allocating Pressure  Drops  to  Control
     Valves."  Instrumentation Technology,  October 1970,  p.  102.

6.   Baumann, Hans D.   "How to Estimate Pressure  Drop Across
     Liquid - Control  Valves."  Chemical Engineering, April  29,
     1974, p. 137.

7.   Kern, Robert.  "Control Valves in process plants."
     Chemical Engineering, April 14,  1975,  p.  85.

8.   Rezac, Mark A. and Kevin P. Bornhoft.   "Choose  the  Right
     Control Valve for the Job."  In-Tech,  October,  1980, p. 59.

9.   Vendor Literature from:  Fisher  Controls, Masoneilan
     International and Pratt Valve.

10.  Driskell, Les, Control Valve Sizing, ISA, 1982.

11.  Driskell, Les, Introduction to Control Valves,  ISA,  1981.

12.  Driskell, Les, Selection of Control Valves,  ISA, 1982.

13.  Chaflin, Sanford.  "Specifying Control Valves."  Chemical
     Engineering, October 14, 1974, p. 105.

14.  Wolter, D. G.  "Control valve Selection."  Instrumentation
     Technology. October, 1977, p. 55.

15.  Wing, Paul.  "Plain Talk on Valve Rangeability."
     Instrumentation Technology, April, 1978,  p.  53.
                     250

-------
11.0 CONTROL VALVE OPERATORS


     11.1 ELECTRIC

          A.   Application

               Characteristics of an electric control valve operator  are:

               1.   Normally economical only in relatively small  torque
                    requirements.

               2.   Large units requiring high torque generally operate
                    slowly.

               3.   Large units weigh considerably more  than  their pneumatic
                    counterparts.

               4.   Normal fail-safe position action is  loclc-in-last-state.

               5.   Major advantage is in remote  installations where  no
                    other power source  (e.g., air supply for  pneumatic
                    operators) is available.
                     TABLE 11.1.   ELECTRIC VALVE OPERATORS
                            APPLICATION GUIDELINES

                    Recommended                     Not Recommended
          In remote, nonhazardous            In explosion-hazard  locations
          installations                        - Digesters
            - Pump stations                    - Oxygen  plants
          In nonexplosion-hazard               - Incinerators
          processes                          For not  environment
            - Primary treatment
            - Most secondary  treatment
            - Tertiary treatment
            - Chlorination
          For cold or damp environment

          B.   principle of Operation

               1.   On/off operation.

                    Electrically actuated  valves use  a. reversing  electric
                    motor to  drive a gear  box or other mechanical
                    positioning mechanism  to open  or  close  a valve.   The
                    motor is  controlled by relay contacts or a  reversing
                    motor starter  that is  interlocked to stop  the valve
                    motor once the valve reaches a fully open  or  closed
                    position.  Adjustable  limit switches detect the  fully
                    open or closed position of the valve.
                                    251

-------
          Electrically operated valves generally require
          high-torque cutout switches in series with the reversing
          starter to prevent damage to the motor and operating
          mechanism if the valve becomes obstructed or jammed.

     2.   Modulating operation.

          Electrically actuated modulating valves use a reversing
          electric motor to operate the valve.  The motor  is
          controlled by a solid-state reversing motor starter that
          starts the valve positioning motor in the required
          direction when a contact closure is initiated.   The
          motor will continue to operate and change the valve
          position as long as the contact closure is maintained.
          When the operating contact is opened, the valve
          positioning motor will stop.  A valve position
          transmitter provides signal condition-ing to generate an
          output signal proportional to the valve position.

C.   Valve Operation

     Valves can be operated using optional pushbuttons mounted in
     the operator or from a remote position control.
     Controllability is good, and accurate position control can  be
     obtained.

     Figure 11.1 provides an example of a typical electrically
     actuated modulating valve interface.

D.   Manufacturer's Options

     1.   Open/Close limit switches:

          a.   Cam-operated, or

          b.   Snap action.

     2.   Position potentiometer typically 0-1000 OHMS to
          correspond to 0-100% open.

     3.   Housings:

          a.   NEMA 12, dustproof,

          b.   NEMA 4, weatherproof, and

          c.   NEMA 7, explosionproof.
                          252

-------
                                        ©
                                     SOLID STATE
                                REVERSING MOTOR STARTER
                                   TRIGGER CIRCUIT
                                      (NOTE 2)

©
LS




CSC
lg—1 p— 13


©
'©x

® POSITION j(D
TRANSMITTER /^>

, 	 INDICATOR
.. L
                                            14-20 MA)
                                          NOTE(S)

                                            I) COMPUTER OUTPUT CONTACTS ARE MAINTAINED
                                             CLOSED QURINO CONTROL.
                                            2) POWER WIRING FOR VALVE MOTOR MAS
                                             MOT BEEN SHOWN
     Q LOCATED »r «LVC

     (f) LOCATIO AT LOCAL PANEL

     d) UJCATCO AT COMPUTER INTERFACE

     g COMPUTER INTERFACE TERMINALS
Figure  11.1.   Electric  operator  control  circuit-modulating service,
                                            253

-------
     4.   power supply:

          a.   115 VAC, two phase, 60 Hz,

          b.   208 VAC, three phase, 60 Hz,

          c.   240 VAC, three phase, 60 Hz,

          d.   480 VAC, three phase, 60Hz, or

          e.   48 VDC.

     5.   Mechanical brakes to lock a valve in position..

     6.   A solid state position controller with an analog
          (usually 4-20 mA) remote setpoint.

     7.   Housing heaters  to prevent condensation, reduce relative
          humidity, and keep lubricants at proper viscosity.

     8.   Motor rated for continuous modulating duty.

E.   Installation

     1.   Size operator for the corresponding valve and  service
          conditions.  Operators are rated by torque which  is
          determined for each application.  Reference  the sections
          on control valves.

     2.   The operator torque rating must exceed the highest
          expected valve torque, and the motor must not  overheat
          in the maximum stroke time under the average expected
          torque.  Furthermore, the motor must perform adequately
          at ^10% of rated voltage.  Most operator manufacturers
          have tables that build in safety factors for the  various
          types of valves.  These tables let you select  operator
          size directly from valve size or from valve  torque data.

     3.   Frequently, placement of the valve in piping galleries
          or new process equipment restricts the operator
          dimensions and weight.  Most often, the smallest  and
          lightest operator with sufficient torque is  selected for
          the application.

F.   Designer Checklist

     Ask the following questions when reviewing or planning an
     electric valve operator installation.  If an answer is "no,"
     an electric operator may not be appropriate.

     1.   Is there a reason pneumatic operators are not  suitable
          for the application?

     2.   Is the highest valve torque in the range of  200 - 5500  J
          (150 - 4000 in-lbs)?

                          254

-------
     3.   Is a positioner required?  Note:  Many manual  loading
          stations provide similar functions with contact  closure
          or triac interfaces, so the positioner is not  required.

     4.   Is adequate power available?

     5.   Are limit switches or position  feedback specified  for
          remote monitoring?

     6.   Is the gear train between the actuator motor and valve
          stem adequate?

     7.   Is the fail-safe condition to hold the last position?
          If not, backup power such as batteries is required.
          Some spring return electric operators are available,  but
          review the application to check on merits of electric
          operators versus other types of opera-tors.  Also
          consider plumbing changes in the valve's location  so  a
          maintained position is a fail-safe position.

G.   Deficiencies

     1.   Modulating service operators overheat due to too small
          operator size.

     2.   Modulating service operators fail frequently.
                          255

-------
11.2 HYDRAULIC

     A.   Application

          Characteristics of a hydraulically actuated valve operator
          are:

          1.   High-pressure hydraulic fluid is generally supplied from
               a common pumping unit.

          2.   Actuator control is accomplished through a valve
               positioner or a system of hydraulic pilot valves.

          3.   Excellent throttling control features due to high
               stiffness (e.g., resistance to changing valve body
               forces).

          4.   Capable of high-torque outputs.

          5.   High initial cost.

          6.   Normal fail-position action of hold, fail open or fail
               close.

     B.   Principle of Operation

          Hydraulically actuated valves use a piston operator to open
          or close the valve.  Separate solenoid pilot valves direct
          hydraulic fluid to one side of the piston to operate the
          valve.  Adjustable limit switches on the valve actuator close
          the pilot valve when the valve reaches its desired position.
          Hydraulic pressure in the cylinder is maintained or vented
          mechanically to hold the desired valve position.  SEE FIGURE
          11.2,
                                 256

-------
             RETURN
             SPRING
                                  SUPPLY
                                   PORT
                                      STEM
                                             •PISTON
                                              0-RING
                           SPRING RETURN
                SUPPLY
                PORT
                                       GUIDE ROD
          DRIVE
          SHAFT
                                           PISTON
                                        SCOTCH
                                         YOKE
                SUPPLY
                 PORT
                       DOUBLE ACTING
    Figure  11.2,   Hydraulic piston actuator.

Hydraulically  actuated modulating valves are  typically
butterfly,  ball,  and  plug type valves.  Solenoid  control
valves direct  regulated hydraulic fluid to either  side of
piston operator  or  a  valve positioner to position  the valve.
When a contact closure is initiated, the appropriate solenoid
valve port  will  open,  and the cylinder will move  the valve
operator until the  limit contact is opened or  the  desired
position is reached.
                       257

-------
     Adjustable limit switches detect the fully open or closed
     position of the valve.   A valve position potentiometer
     provides a resistance output signal proportional to the valve
     position for remote monitoring.

C.    Valve Operation

     Operation is normally from a local or remote panel external
     of the valve.

     Controllability is good, and accurate position control can be
     obtained.
     For interfacing,  see Figure 11.3 for example of valve actuators
     that use solenoid control valves.   Contact closure signals would
     be connected directly to the solenoid valves.located on or near
     the modulated valve.
                           258

-------
                      HYDRAULIC OR    <«-»> «•*'
                     "PNEUMATIC SUPPLY
O LOCATED AT VALVE

(D LOCATED AT LOCAL PANEL

© LOCATED AT COMPUTER INTERFACE

fxl COMPUTER INTERFACE TERMINALS
                                              NOTE(S)
                                                I) COMPUTER OUTPUT MAINTA!N£L
       Figure  11.3.    Piston actuator  control  circuit -
                         incremental  modulating  service.
                                    259

-------
11.3 PNEUMATIC

     A.   Application

          Pneumatic valve operators are available in two types.  First
          is the piston actuator, shown in Figure 11.5, which  is the
          same as the hydraulic actuator  (Figure 11.5).  Second is  a
          diaphragm actuator as shown in Figure 11.6.

          Cnaracteristics of a pneumatic control valve operator are:

          1.   pneumatic piston.

               a.   Used open/close or modulating duty.

               b.   Used when thrust or torque requirements exceed  the
                    capaoility of spring-and-diaphra
-------
                                     • SUPPLY PORT
               SPRING
                           %3 Y///////77/77,
                                          STEM
                                                  O-RING
                              SPRING RETURN
     PISTON
      
-------
              UPPER CASING
DIAPHRAM
   SPRING
                                      SUPPLY PORT
                                           LOWER CASING
                                         STEM
                           LINEAR ACTUATOR
                                        SUPPLY PORT
                                          SPRING

                                         LOWER CASING
DIAPHRAM
                 DRIVE ARM
               DRIVE SHAFT-


                    ROTARY OR QUARTER-TURN ACTUATOR
             Figure 11.5.  Diaphragm actuator.

     Adjustable limit  switches detect the fully open or  closed
     valve position.   A  valve position transmitter with
     appropriate signal  conditioning provides a 4 to 20  ma output
     signal, proportional  to the valve position, for control
     purposes.

     Pneumatically actuated  modulati.^ valves are typically
     mechanically operated butterfly,  ball, and plug type  valves
     or bladder type pinch valves.   Separate solenoid  control
     valves direct regulated compressed air to the valve
     positioner to position  the valve.  When a contact closure is
     initiated, the appropriate solenoid valve opens and the
     cylinder moves the  valve operator until the contact is opened.

C.   Valve Operation

     Remote position control from an external source is  available.

     Controllability is  good, and accurate position control can be
     obtained.

-------
                                  APPENDIX A

                               TITLE 3Y SUBJECT

                                REFERENCE LIST
Activated Sludge Wastewater Treatment Plants, Design Handbook for
     Automation of.  Manning, A,W., Dobs, D.M.  EPA-600/8-80-028 1980.

     Reference Order 120, Appendix B
Analog & Digital Control, Combined.  Murray, J.J.  Chemical Engineering,
     June 1976.

     Reference Order 16, Appendix B
Automatic Control—Reprint from Chemical Engineering.  Soule, L.M.
     Foxboro Company, 1970.

     Reference Order #13, Appendix B
Automatic Process Control.  Johnson, E.F.  McGraw-Hill, 1967.

     Reference Order 118, Appendix B
Automatic Process Control, Principles of.  Instrument Society of  America.
     ISBN 87664-108-7, 1968,

     Reference Order #17, Appendix 3
Closed Loop Control System:  Operation of a Direct-Digital On-Line Closed
     Loop Control System for Wastewater Treatment.  Nelson, J.K.,
     Mishra, B.B.  Conference Presentation, Oct.  1978.

     Reference Order #26, Appendix B
Control Theory Notebook.  Wilson, H.S., Zoss, L.M.  Reprinted from  ISA
     Journal.

     Reference Order #19, Appendix B
                                     263

-------
                               TITLE BY SUBJECT
Control Valves, Allocating Pressure Drops to.  Moore, Ralph W.
     Instrumentation Technology, Oct. 1970, p. 102.

     Reference Order #17, Appendix B
Control-Valve Gain, The Effect of Installed Flow Characteristic on.
     Boger, Henry w,  ISA Transactions Vol. 8, No. 4, 1969, p. 265.

     Reference Order 117, Appendix B
Control Valves and Pumps:  Partners In Control.  Coughlin, -John L.
     Instruments and Control Systems, Jan. 1983, p. 41.

     Reference Order 116, Appendix B
Control Valve:  Choosing a Control Valve is Easy.  Hanunit, Donn.   Instrument
     and Control Systems, Dec. 1976, p. 28.

     Reference Order #16, Appendix B


Control Valve, Choosing the Right Control Valve for the Job.  Rezac,  Mark  A.,
     Bornhoft, Kevin F.  In-Tecn, Oct. 1980, p. 59.

     Reference Order 117, Appendix B
Control Valves In Process Plants.  Kern, Robert.  Chemical Engineering,
     April 1975, p. 85.

     Reference Order 16, Appendix B
Control Valves, Introduction to.  Driskell, Les.  Instrument Society of
     America, 1981.

     Reference Order #17, Appendix B
Control Valve Selection.  Wolter, D.G.  Instrumentation Technology,
     Oct. 1977, p. 55.

     Reference Order #17, Appendix B
                                     264

-------
                               TITLE BY SUBJECT
Control Valves, Selection of.  Driskell, Les.  Instrument Society of  America,
     1982.

     Reference Order #17, Appendix 3
Control Valves, Sizing.  Driskell, Les.  Instrument Society of America,  1982.

     Reference Order #17, Appendix B


Control Valves, Specifying.  Chaflin, Sanford.  Chemical Engineering,
     Oct. 1974, p. 105.

     Reference Order #6, Appendix 3


Digital Computer Process Control.  Smith, C.L.  In-Tech, 1972.

     Reference Order #17, Appendix B
Dissolved Oxygen Field Test Protocol, Evaluation of.  Kulin, G.,
     Schuk, W.W.  EPA 78-D-X0024-1, 1978.

     Reference Order #25, Appendix B
DO Analyzers, Comparison of Field Testing on.  APWA Research  Foundation,
     Sept. 1982.

     Reference Order #1, Appendix B


Effluent Specs:  Tight Effluent Specs Met With Digital Control.
     Robbins, M.H.  Water/Engineering & Management, Oct. 1983,

     Reference Order #22, Appendix B
Electromagnetic Flow Meters In Wastewater Treatment Plants, Recommended
Practice For The Use of.
     Kulin, G.  EPA-600/2-34-187, November, 1984

     Reference Order #20, Appendix B
                                      265

-------
                               TITLE BY SUBJECT
Energy Conservation for Existing Wastewater Treatment Plants.
     Burns, Bruce E.  Journal WPCF, Vol. 53, No. 5, May 1981, p. 5.

     Reference Order #26, Appendix B


Flow;  Its Measurement and Control in Science and Industry, Vol.  2.
     Instrument Society of America, 1981.

     Reference Order f!7, Appendix B
Flow Measurement HandbooK, Open Channel.  Grant, D.M.   ISCO,  Inc.
     2nd Edition, 1981.

     Reference Order #15, Appendix B


Flow Measurement;  Parsnall Plume, Standard Method for Open Channel Flow
     Measurement of Industrial Water and Industrial Wastewater.
     ASTM D1941-67.

     Reference Order #4, Appendix B


Flow Measurement In Wastewater Treatment Plants with venturi  Tubes and
     Venturi Nozzles, Recommended practice For.
     Kulin, G.  EPA-600/2-84-185, November, 1984.

     Reference Order #20, Appendix B.


Flow Meter Engineering Handbook.  Honeywell, Inc., 5th Edition,  1977.

     Reference Order #14, Appendix B


Flow Meter Engineering, Principles and Practice of. Spink, L.K.
     Foxboro Co., 9th Edition, 1967.

     Reference Order #13, Appendix B


Flow Meters In Wastewater Treatment plants, Recommended Practice For The Use
     of Electromagnetic.      ——-
     Kulin, G.  EPA-600/2-84-187, November, 1984.

     Reference Order #20, Appendix B
                                   266

-------
                               TITLE BY SUBJECT
Flow Monitor Device, Choosing.  Hall, J.  Instruments and Control Systems,
     June 1978.

     Reference Order #16, Appendix 3
Flcwmeter Accuracy, piping Arrangements for Acceptable.  Sprenkle, R.E.
     ASME Transactions 67:345, 1945.

     Reference Order #10, Appendix B
Flowmeters to Water Management Systems,  Application of.   Brown,  A.E.
     Instrument Society of America,  Oct. 1981.

     Reference Order |17, Appendix B
Flowmeters, Ultrasonic;  Basic Design, Operation and Criteria Application.
     Powell, D.J.  Plant Engineering, May 1979.

     Reference Order #21, Appendix B
Fluid Meters, Their Theory and Application.   ASME Report on Fluid Meters.
     6th Edition, 1971.

     Reference Order 13, Appendix B
Flumes In Wastewater Treatment plants,  Recommended Practice For The Use of
     Parsnail Flumes and Palroer-Blowlus.
     Kulin, G.  EPA-600/2-84-186,  November,  1984.

     Reference Order #20, Appendix B
Industrial Pressure Measurement.  'Gullum,  R.   Instrument Society of America
     Publications,  1982.

     Reference Order 117, Appendix B
Industrial Process Control.   Lloyd,  S.G.,  Anderson,  G.D.   Fisher  Controls,
     1971.

     Reference Order 112, Appendix B
                                   267

-------
                               TITLE BY SUBJECT
Instrument Engineers Handbook, Process Measurement.  Liptak, B.C.,
     Venczel,  K.   Chilton Book Co., 1969, Revised 1982.

     Reference Order 17, Appendix B
Instrumentation In Wastewater Treatment Plants.  Manual of Practice No. 21.
     Water Pollution Control Federation, 1978.

     Reference Order 126, Appendix B
Liquid Plow Instruments, Meter Runs.  Foxboro Technical Bulletin 8-110,
     Feb. 1943,

     Reference Order #13, Appendix B
Liquid Flow Measurement.  Foxboro Technical Bulletin 8-251, Aug. 1965.

     Reference Order #13, Appendix B
Magnetic Flow Meter.  Fischer & Porter Instruction  Mo.  10D1435  A,,
     Revision 1, 1969.

     Reference Order til, Appendix B
Magnetic Flow Meter—Application.  Sybron/Taylor Corp.   Product  Data,
     PDS-15E002, Issue  3.

     Reference Order #23, Appendix B
Magnetic Flow Meter—Basic Theory.  Sybron/Taylor Corp.  Product  Data,
     PDS-15E001,  Issue 3.

     Reference Order #23, Appendix B
Magnetic Flow Meter—Installation.  Sybron/Taylor Corp.   Product  Data,
      PDS-15E003,  Issue  2,

      Reference  Order #23,  Appendix  B
                                      268

-------
                               TITLE BY SUBJECT
Minicomputers in Industrial Control.  Harrison, T.V.  Instrument Society of
     America, 1978.

     Reference Order $17, Appendix B


Orifice and Venturi Meters, Survey of Information Concerning the Effects
     of Nonstandard Approach Conditions.  Starret, P.S., Halfpenny, P.F.,
     Noltage, H.B.  ASME 1965.

     Reference Order flO, Appendix B


Orifice Plates for Flow Measurement, Flange Mounted snarp Edged,  instrument
     Society of America, RP 3.2-1978.

     Reference Order $17, Appendix B
Parshall Plumes and Palmer-Bowlus Flumes in Wastewater Treatment plants,
     Recommended Practice For The Use Of.
     Kulin, G.  EPA-600/2-84-186, November, 1984.

     Reference Order 120, Appendix 3
Process Control;  Basic Concepts, Terminology and Techniques for.
     Gordon, Lewis M.  Reprinted from Chemical Engineering, May 1983, p.  58.

     Reference Order $13, Appendix B
Process Control Computer Systems Guide for Managers.  Stire, T.G.
     ISBN 250-40488-5.

     Reference Order #5, 9, Appendix 3
Process Control Systems.  ShinsXy, F.M.   McGraw-Hill,  2nd Edition, 1979,

     Reference Order $18, Appendix B
Process Instrumentation Manifolds.   Benson,  J.E.   Instrument Society of
     America, 1978.

     Reference Order |17, Appendix B
                                   269

-------
                               TITLE BY SUBJECT
Process Instruments and Control Handbook.  Considine, D.M.  McGraw-Hill,
     2nd Edition, 1974.

     Reference Order 118, Appendix B
Refinery Instruments and Control Systems;  Manual on Installation of.
     Part I—Process Instrumentation and Control, Section 1—Flow.
     API RP550, 3rd Edition, 1977.

     Reference Order 12, Appendix B
Refinery Instruments and Control Systems;  Manual on Installation of.
     Part I—Process Instrumentation and Control, Section  2—Level.
     API 1974.

     Reference Order #2, Appendix B
Refinery Instruments and Control Systems:  Manual on Installation of.
     Part I, Section 6—Control Valves and Accessories.  API, 3rd Edition,
     1976.

     Reference Order 12, Appendix B
Refinery Instruments and Control Systems:   Manual  on  Installation  of.
     Part  II—Process Stream Analyzers.  API RP550, 3rd  Edition,  1977.

     Reference Order #2, Appendix B


Three Mode Controllers, Fundamentals of.   Jury,  P.O.   Technical  Monograph  28,
     Fisher Controls, 1973.

     Reference Order *12, Appendix B


Tuning Controllers for Noisy Processes.  Fertik, H.A.   ISA  Transactions,
     Vol.  14, No. 4, 292-304,  1975.

     Reference Order 117, Appendix B
Ultrasonic  Flowmeters;   Basic  Design,  Operation  and  Criteria  Application.
     Powell,  D.J.   Plant  Engineering,  May 1979.

     Reference  Order  121,  Appendix  B

                                      270

-------
                               TITLE BY SUBJECT
Valve;  Advances In Water and Wastewater Valves.  Consulting Engineer,
     Sept. 1982, p. 105.

     Reference Order #8, Appendix B


Valve Rangeability, Plain Talk on.  Wing, Paul.  Instrumentation Technology,
     April 1978, p. 53.

     Reference Order |17, Appendix B


Valves With process Requirements, Matching.  Ramsey, Jonn.R.,
     Fournier, Charles D.  Instrument and Control Systems, June 1973, p. 65.

     Reference |16, Appendix B
Venturi Meter Tube, Standard Methods of Flow Measurement of Water.
     ASTM D2458-69.

     Reference Order $4, Appendix 3


Venturi Tubes and Venturi Nozzles, Recommended practice.For Flow Measurement
     In Wastewater Treatment Plants With.
     Kulin, G.  EPA-600/2-84-185.  November, 1984.

     Reference Order #20, Appendix B
Water Measurement Manual.  U.S. Department of the Interior, Bureau of
     Reclamation, 2nd Edition, 1981.

     Reference Order |24, Appendix B
                                   271

-------
                                   APPENDIX B

                             REFERENCE LIST SOURCES



Reference f                       Available From;

     1                            American Public Works Association
                                  1313 East 60th Street
                                  Chicago, IL  60637

                                  (312)  667-2200
                                  American Petroleum Institute
                                  Publication and Distribution Section
                                  2101 L Street NW
                                  Washington, DC  20037

                                  (202) 457-7160
                                  American Society of Mechanical Engineers
                                  Order Department
                                  United Engineering Center
                                  P.O. Box 3199
                                  New York, NY  10163
                                  American Society for Testing and Materials
                                  1916 Race Street
                                  Philadelphia, PA  19103

                                  (215) 299-5400
                                  Butterworth Publishers
                                  c/o EMA, Inc.
                                  Hanover Building
                                  480 Cedar Street
                                  St. Paul, MN  55101

                                  (612) 298-1992
                                  Chemical Engineering, 43 PL
                                  1221 Avenue of the Americas
                                  New York, NY  10020
                                     272

-------
Reference t                       Available From:

     7                            Chilton Book Company
                                  Chilton Way
                                  Radnor, PA  19039

                                  (215)  964-4729
                                  Consulting Engineer
                                  1301 S. Grove Avenue
                                  P.O. Box 1030
                                  Harrington, IL  60010

                                  (312) 331-1840
                                  EMA, Inc.
                                  Hanover Building
                                  480 Cedar Street
                                  St. Paul, MN  55101

                                  (612) 298-1992
      10                           Engineering Societies Library
                                  345th East 47th Street
                                  New York, NY  10017

                                  (212) 705-7606
     11                           Fischer & Porter
                                  25 Jacksonville Road
                                  Warminster, PA  18974
      12                           Fisher Controls Company
                                  205 South Center Street
                                  Marshalltown,  IA  50158
      13                            Foxboro Company
                                   Literature  Stock Department 544
                                   P.O. Box  568
                                   Foxboro,  MA   02035

                                   (617)  543-8750
                                     273

-------
Reference f                       Available From:

     14                           Honeywell, Inc.
                                  Publications
                                  Fort Washington,  PA  19034

                                  (215) 641-3000  '
     15                           ISCO, Inc.
                                  P.O.  Box 82531
                                  Lincoln, ME  68528

                                  1-800-228-4373
                                  (402) 464-0231
     16                           Instrument & Control Systems
                                  (Chilton's I&CS)
                                  •-nilton Co.
                                  Radnor, PA  19089

                                  (215)  964-4496
     17                           Instrument Society of America
                                  67 Alexander Drive
                                  P.O. Box 12277
                                  Research Triangle Park, NC  27709

                                  (919) 549-8411
     18                           McGraw-Hill Publications Co.
                                  1221 Avenue of the Americas
                                  New York, NY  10020

                                  (212) 997-1221
     19                           Moore Products Co,
                                  Sumney Town Pike
                                  Springhouse, PA  19477

                                  (215) 646-7400
      20                           National Technical Information Service
                                  5285 Port Royal Rd.
                                  Springfield, VA  22161

                                  (703)  487-4650

                                     274

-------
Reference #                       Available From:

     21                           Plant Engineering
                                  1301 S.  Grove Avenue
                                  P.O. Box 1030
                                  Harrington,  IL  60010

                                  (312) 381-1840
     22                           Water,  Engineering & Management
                                  Scranton Gillette Communications, Inc.
                                  380 Northwest Highway
                                  Des Plaines,  IL  60016
     23                           Sybron/Taylor Corp.
                                  100 Midtown Tower
                                  Rochester, NY  14604

                                  (716)  546-4040
     24                           Superintendent of Documents
                                  U.S. Government Printing Office
                                  Washington,  DC  20402
     25                           United States Environmental Protection Agency
                                  26 West St.  Clair Street
                                  Cincinnati,  OH  45268

                                  (513)  684-2621
     26                           WPCF
                                  2626 Pennsylvania Avenue NW
                                  Washington,  DC  20037

                                  (202)  337-2500
                                     275

-------
                                   GLOSSARY
access time:  1. The time it takes a computer to locate data or an
     instruction word in its storage section and transfer  it to its
     arithmetic unit where the required computations are performed.   2.  The
     time it takes to transfer information which has been  operated on from
     the arithmetic unit to the location in storage where  the  information is
     stored.

accuracy:  The maximum error in the measurement of a physical  quantity in
     terms of the output of an instrument when referred  to the individual
     instrument calibration.  Usually given as a percentage of full  scale.

actuator:  A mechanism for translating an electronic or pneumatic  signal
     into a corresponding movement or control.  Example:   an actuator moves
     a valve based on a control signal.  See also final control element.

address:  A numerical expression which designates a specific location in
     stored memory (software), or a specific card and pin  number  (hardware).

alarms:  Devices which signal the existence of abnormal conditions.   See
     also annunciator.

algorithm:  A prescribed set of rules or procedures for  tiie solution of  a
     problem in a finite number of steps.

alphanumeric:  Pertaining to a character set that contains both letters  and
     numerals and other characters such as punctuation marks.

amplifier:  A device that enables an  input signal  to control power from a
     source independent of the input  signal and thus be capable of
     delivering an output that bears  a relationship to,  but is generally
     greater than, the input signal.

analog:  Pertaining to representation of numerical quantities  by  means of
     continuously variable physical characteristics.  Contrast with digital.

analog control:  Implementation of automatic control loops with analog
      (pneumatic or electronic) equipment.

analog device:  A mechanism which represents numbers by  physical
     quantities, i.e., by lengths, as in a slide  rule, or  by voltage or
     currents as in a differential analyzer or  a  computer  of  the  analog type.

analog signal:  A continuously varying representation of  a physical
     quantity,  property, or condition such as  pressure,  flow,  or
      temperature.  The signal may be  transmitted  as pneumatic, mechanical,
     or  electrical energy.
                                    276

-------
analog-to-digital converter  (ADC):  A device used  to convert  an  analog
      signal to approximate corresponding digital  data.

annunciator:  A visual or audible signaling device and  the  associated
      circuits used for indication of alarm conditions.

application software:  Programs which are unique  to a specific process
      control system installation or other specific installations,  rather
      than general purpose and of broad applicability.

assembler:  A software program that translates symbolic  language into
      machine language by the substitution of operation  codes for symbolic
      operation codes and absolute or relocatable  addresses for  symbolic
      addresses.

asynchronous transmission:  Transmission in which  each  information
      character, word, or block of data is individually  synchronized,
      usually by the use of start and stop elements.  Time  between
      transmission of characters can vary.

automatic:  Pertaining to a process or device that under specified
      conditions, functions without intervention  by a human operator.

background processing:  A processing method whereby some computer programs
      with a low priority are executed only when  the computer is not busy
      with execution of higher priority programs.

backup:  provisions for an alternate means of operation  in  case  of
      unavailability of the primary means of operation.

batch processing:  1. pertaining to the technique  of executing a set of
      programs, such that each is completed before the  next program of the
      set is started.  2. Loosely, the execution  of programs  serially.

baud rate:  A unit of signaling speed indicating  the number of signal
      changes per second.  Most signal schemes have two  states representing
      a bit equal to 1 or 0.  In this case bit rate equals  baud  rate.  Some
      signaling schemes have multiple states.  In these, baud rate  is less
      than bit rate.

binary coded decimal (BCD):  Describing a decimal  notation  in which
      individual decimal digits are represented by a group  of binary bits,
      e.g., in the 8-4-2-1 coded decimal notation  each  decimal digit is
      represented by a group of four binary bits.  The  number twelve is
      represented as 0001 0010 for 1 and 2, respectively, whereas in binary
      notation it is represented as 1100.

binary number:  A number usually consisting of more than one  figure,
      representing a sum, in which the individual  quantity  represented by
      each figure is based on a radix of two.  The figures  used  are 0 and 1.
                                    277

-------
bit:  1. An abbreviation of binary digit.  2. A single character  in  a
      binary number.  3. A single pulse in a group of pulses.   4. A  unit of
      information capacity of a storage device.  The capacity  in  bits is the
      logarithm to the base two of the number of possible  states  of  the
      device.  Related to storage capacity.  5. One binary digit, the
      smallest piece of information in a computer system.  A bit  can be
      either 1 or 0.

bit rate:  Rate at which binary digits are transmitted over a  communications
      link.  (See baud rate.)

block transfer:  The process of transmitting one or more groups of data.

boiler plate:  Common expression referring to standard written requirements
      or regulations, usually inserted in the front of a contract or
      specification.

Boolean:  An algebraic system formulated by George Boole for formal
      operations on true/false logic.

buffer:  1. An internal unit of a computing device which serves as
      intermediate storage between two storage or data handling operations
      with different access times or formats; usually to connect  an  input or
      output device with the main or internal high-speed storage.   2. An
      isolating component designed to eliminate the reaction of a driven
      circuit on the circuits driving it, e.g., a buffer amplifier.

bumpless transfer:  A characteristic of a controller which permits control
      mode changes  (such as automatic or manual selection) to  be  made
      without producing a discontinuity in the controller  output.

byte:  1. A generic term to indicate a measurable portion  of a string of
      two or more binary digits, e.g., an 8-bit byte.  2.  A group of binary
      digits usually operated upon as a unit.

cascade control:  The use of two conventional feedback controllers  in series
      such that two loops are formed, one within  the other.  The  output of
      the controller in the outer loop modifies the setpoint of the
      controller in the inner loop.

cathode ray  tube  (CRT):  1. An electronic vacuum  tube containing  a  screen
      on which information may be stored for visible display by means of a
      multigrid modulated beam of electrons  from  the  thermionic emitter.  2.
      Loosely, a computer terminal using a cathode  ray tube as a  display
      device.

central processing  unit  (CPU):  A unit of a  computer  that  includes  circuits
      controlling the interpretation and execution  of  instructions.

character:   One alphanumeric symbol, e.g., letter,  figure, number,
      punctuation or other  sign.  Characters  are  usually represented by a
      code of binary digits, e.g., ASCII.


                                    278

-------
closed-loop:  A signal  path  which  includes a forward path,  a feedback path,
       and  a  summing  point, and forms a closed circuit.

common mode  rejection (CMR):   The  ability of a circuit  to discriminate
       against a common  mode  voltage.  CMR may be expressed as a
       dimensionless  ratio, a  scalor  ratio, or in decibels.

common mode  voltage:  A voltage relative to ground of the same polarity on
       both sides of  a differential input.

compiler:  A program that  translates a problem-oriented language to a
       machine oriented  language, such as FORTRAN, and substitutes
       subroutines  and single  machine instructions for symbolic inputs.

computer:  1. A data  processor that  can perform substantial computation,
       including numerous arithmetic  or logic operations,  without
       intervention by a human operator during the run.   2.  A device capable
       of solving problems  by  accepting data, performing described operations
       on the data, and  supplying the results of these operations.  Various
       types of  computers are  calculators, digital computers and programmable
       controllers.

control:   1. in process control, this refers to actions taken to achieve a
       desired result  in the process.   2.  In some applications, a mathematic
       check.  3. In  computer  programs,  instructions which determine
       conditional  jumps are often  referred to as control  instructions, and
       the  time  sequence of execution of instructions is called the flow of
       control.

control loop:   Several  control devices connected in series  to perform a
       specific  control  function.

control mode:   A specific  type of  control action such as  proportional,
       integral  or  derivative.

control sequence:  See  sequence control program.

control strategy:  A  sequence  of instructions (program) executed by a
       computer  to  achieve a desired  control objective.

control system:  1. A system  in which deliberate  guidance or  manipulation is
       used to achieve a prescribed value  of a variable.   2. Refers to a
       system of  hardware and  software components  including  computers,  disks,
       printers,  instruments, control  panels,  operator facilities,
       communications  channels,  systems  programs,  development  programs,  and
       applications programs.

controller:  A device which operates  automatically  to regulate a controlled
       variable by comparing a measurement of  the  variable with a reference
      value representing the desired  level  of operation.
                                       279

-------
cursor:  A marker which moves over a surface  to delineate position.   A dot
      on a CRT screen, for example.

OAS:  Data acquisition system.

DEAC:  Digitally emulated analog control.

data base:  A collection of stored data  in memory  that  is application
      specific for use by the control software - for  example,  remote station
      files that contain input/output point description data  for  each remote
      station.

data highway:  Refers to a coax cable data link connecting  remote processors,
      operator facilities and the central computer  to provide information
      exchange.

deadband:  1. A specific range of values within which the incoming signal
      can be altered without also changing the outgoing response.  2. The
      range of values of a process variable where  no  control  action is
      taken,  if the process variable exceeds the  deadband  high or low
      limits, control action is started,

deadman control:  Continuous manual action  (e.g.,  depressing  a pushbutton)
      is required to modulate device position or speed. Device maintains
      status quo when control action is  absent.

dead time:  The interval of time between initiation of  an  input change or
      stimulus and the start of the resulting observable response.

derivative action:  A controller mode which contributes an  output
      proportional to the rate of change of the error.

development software:  Software which provides a means  for  creation of
      application software, such as a data base generator.

diagnostic:  A computer routine designed to test a hardware or software
      function and identify malfunction  or error.

digital:  Pertaining  to representation of numerical quantities by discrete
      levels or digits conforming  to a prescribed  scale of  notation.

direct acting controller:  A controller  in which the  value  of the output
      signal increases as the value of the  input  (measured  variable)
       increases.

direct digital control  (DDC):  1. A control  technique in which a  digital
      computer  is the controller and  its output  is connected directly to the
      final control element.  Used  to distinguish  from analog control.  2.
      Implementation of analog PID control  using computer  software rather
       than conventional analog controllers  (DEAC).

disk  (or  disc):  A memory storage  device using one or more  rotating plastic
       discs coated with a magnetic material  for  recording  information.

                                   280

-------
distributed control:  Location of controlling equipment  (either  computer  or
      conventional controllers) at remote locations  throughout  the  process.

disturbance:  A change in the operating condition of a process,  most
      commonly a change in input or output loading.

download:  a process by which a CPU in a computer control  system network
      transfers a program (task) image to another CPU in the  network and
      causes it to be executed.

duplex:  See full duplex.

dynamic data:  Data whose value depends on conditions or parameters that
      change with time.  Contrast with fixed or static data.

engineering unit (EGU):  Units of measure of process variables.

error:  The difference between the setpoint reference value and  the value of
      the measured signal.

expendables:  Items expected to be consumed such as print  paper,  lubrication
      fluids, and air filters.  Distinguished from spare parts used for
      replacement of failed components such as printed circuit boards, power
      supplies, and fuses.

failure:  Loss of ability to perform a specified function.

feedback:  The signal in a closed-loop system representing the condition  of
      the controlled variable.

feedback control:  Control in which a measure variable is  compared  to its
      desired value to produce an actuating error signal which acts upon  the
      process to reduce the magnitude of the error.

feedforward control:  Control in which information concerning one or more
      conditions that can disturb the controlled variable  is  converted,
      outside of any feedback loop, into corrective action to minimize
      deviations of the controlled variable.

final control element:  The device used to directly change the value of the
      manipulated variable.

firmware:  A series of computer instructions (programs)   permanently stored
      in BOM (read only memory).

floppy disk:  A small flexible inexpensive magnetic disk commonly used for
      data storage in small computer systems.

flowchart:  1.  A system analysis tool that provides a graphical presentation
      of a procedure.  Includes block diagrams, routine  sequence  diagrams,
      and data flow symbols.  2. A chart to represent for a problem,  the
      flow of data,  procedures, growth, equipment, methods, documents, and
      machine instructions.   3. A graphical representation of a  sequence  of
      operations by using symbols to represent the operations such  as
      compute,  substitute, compare, jump, copy, read, and write.


                                 281

-------
foreground processing:  A nigh-priority processing method where  real-time
      control programs and process inputs are given preference  (tnrough  the
      use of priority interrupts) over other programs being executed  by  the
      computer system.  See bac leg round processing.

full duplex:  A communications channel with separate circuits for
      transmission and reception, so that both can occur simultaneously.
      Also referred to as duplex communications.

graphic:  Pertaining to representational or pictorial material,  usually
      legible to humans and applied to the printed or written form  of data
      such as curves, alphabetic characters, and  radar  scope displays.

naif duplex:  A communications channel where transmission and reception
      share the same circuit so that both cannot  occur  simultaneously.

hand/off/automatic (HDA):  Refers to a 3-position selector switch on  a
      control panel.  In AUTOMATIC a computer or  logic  in the panel control
      the associated device.  In HAND, the device is turned on from the
      local panel.  In OFF, the device state is turned  off from  the local
      panel.

hard coded:  A programming practice whereby application-related  information,
      such as point names, and ranges, are not represented symbolically
      within a program such that recompilation is necessary in order  to
      change the information.

Hertz:  Abbreviated Hz.  A unit of frequency equal to one cycle  per second.

hierarchy:  Refers to levels of supervision and control responsibility
      within a centralized control system.

hierarchical network:  A computer network in which processing and control
      functions are performed at different levels tyy several computers
      especially suited to the functions performed.

incremental control:  Use of short pulses to increase or decrease the value
      of  the controlled variable.  Contrast with  positional control.

input/output list:  A list that describes remote  station and satellite input
      and output signal points containing information such as point label,
      type, address, and limits.

instruction set:  A listing of the instructions or operations a  particular
      computer can execute.

instrumentation:  The application of devices for  the measuring,  recording,
      or  controlling of physical properties and movements.

interlock:  A mechanical or electrical device or  wiring which  is arranged  in
      such a manner as  to allow or prevent operation of equipment only in  a
      pre-arranged sequence.


                                   282

-------
integral action:  A controller mode which contributes  an  output proportional
      to the integral of the error.

integral time:  The time required after  a step  input  is applied for the
      output of a proportional plus integral mode  controller  to change by an
      amount equal to the output duo  to  proportional  action alone.

isolation:   a physical  and electrical  arrangement of the parts of a
     receiving instrument to prevent interference currents within or
     between input and output of the instrument.
lead-lag compensation:  An electronic  network or software used to influcence
      the response of a control loop.

line conditioning:  The addition of equipment to a leased voice-grade
      channel to provide minimum line  characteristics  necessary for data
      transmission.

linearity:  Ability to achieve a straight-line  response to an input signal.

load shedding:  starting and stopping  of equipment to  reduce  electrical
      power demand.

local control:  Control operations performed either manually  or automatically
      at a control panel located near  the process  or  equipment.

logging:  Recording values of process  variables for later use in trending,
      report compilation, or historical  records.

loop:  See control loop.

loop gain:  The ratio of the change in the  return  signal  to the change in
      its corresponding error signal  at  a specified frequency.  Note:  the
      gain of the loop elements is frequently measured oy opening the loop,
      with appropriate termination.   The gain so measured is  often called
      the open loop gain.

machine language:  Coding in the numeric language  form acceptable to the
      computer arithmetic and control  unit.

main frame:  1. The central processor  of the computer  system.  It contains
      the main storage, arithmetic unit  and special register  groups.
      Synonymous with CPU and central processing  unit.  2. All that portion
      of a computer exclusive of the  input,  output, peripheral and in some
      instances, storage units.

manipulated variable:  The process variable that  is changed by the
      controller to reduce or eliminate  error.

manual control:  Control operations are  performed  directly by a human
      operator and not by computer control  algorithms. Two levels of manual
      control are possible;  1. local  manual -  the process is controlled
      manually from the local panel;   2. computer  manual  - the process is
      controlled manually through computer  system  interactive CRT displays.

manual loading station:  A manual electronic controller.   Used here to refer
      to a controller whose output  is  adjusted  manually by an operator from
      the front of a panel.

                                   283

-------
menu:  A CRT screen which lists operator options  available  related to a
      given area.  For example, a graphic menu  lists  all  graphic  displays
      which may be chosen.

modem:  A contraction of modulator/demodulator.   This is  a  device that
      converts digital data into a form suitable  for  transmission ovar the
      communications media.  For example, phone line  modems convert digital
      data to audio signals.

monitoring:  The information on the conditions  of various water control
      processes, operations, levels, and security obtained  by electronic
      devices.

multi-drop network:  A type of communications  system  where  lines  are
      terminated (dropped) at intermediate  points between the end terminals
      of the system.

multiplexer  (MUX):  A device which samples  input  and/or output channels and
      interleaves signals in frequency or time.

multiplexing:  The process of combining several measurements for
      transmission over a pair of wires or  link.

multi-processing:  Pertaining to the apparent  simultaneous  execution of two
      or more programs or sequences of instructions by a  computer or
      computer network.

multi-programming:  pertaining to the  apparent  simultaneous execution of two
      or.more programs by a single computer.

multi-tasking:  The facility  that allows  the programmer to  make use of the
      multi-programming capability of  a system.

normal mode  voltage:  A voltage induced across  the input  terminals of a
      device.

OOC:  Optimizing digital control.

offset:  The steady-state deviation of the  controlled variable from the
      setpoint caused by a change  in load.

on-line:   Pertaining  to a computer  that  is  actively monitoring or
      controlling a process or operation,  or pertaining to  a capability of
      the  user  to  interact with a  computer.

on/off control:  A  system of  regulation  in which the  manipulated variable
      has  only  two  possible  values,  on and off.

open-loop:   A  signal  path without  feedback.

operating  limits:   High  and  low limits set for a process  variable.  A value
      of process variable between  these  limits is considered normal and no
      control  action  is  taken.  When  either of the limits  are exceeded an
      alarm  or  control  action is  initiated.


                                   284

-------
operating system:  Software that controls  the carrying out  of  computer
      operations such as scheduling, compilation,  storage assignment, and
      data management.

operator interface (operator process interface):   The means through which an
      operator accesses tne computer system  to  affect process  control
      actions.  Usually this consists of a CRT  and Keyboard arrangement
      along with appropriate display software.

optimization:  A process whose object is to  make one or  more variables
      assume, in the best possible manner, the  value best suited to the
      operation at hand, dependent on the  values of certain other variables
      which may be either predetermined or sensed  during the operation.

package system:  Equipment which is supplied as a  system including controls.

parallel transmission:  A mode of transmission  whereby each bit  of a data
      word is transmitted simultaneously over separate communications
      circuits.
                                                      •
parameters:  The limits or context within  which the problem is considered.

parity:  One method of error checking in data communications.  As a bit
      string is transmitted, an extra bit  is added to make  the total number
      of bits either odd or even (called odd or even parity).  The receiving
      machine checks each bit string for correct parity.

peripheral:  A machine that enables a computer  to  communicate  with the
      outside world or aids the operation  of the computer.

permissive:  A signal which permits the placing of equipment into operation.

piping and instrumentation drawing  (P&ID):   A schematic  drawing  of tne
      process showing, all liquid flow paths, location of all sensors and
      instruments, and location of backup  conventional control equipment.

point:  A single signal to or from a field device,  points  are either analog
      in, contact  (digital) in, modulating (analog) out, or contact
      (digital) out.

polling:  Periodic interrogation of each of  the terminals that share a
      communications channel to determine  whether  it needs  to  use the
      channel to transmit.  An alternate to  a contention system  of
      communication channel control.

positional control:  Use of a maintained signal output value to  modulate
      device position or speed.  Contrasts with incremental control.

power management:  Making most efficient use of operational periods for
      equipment and using tne lower cost rate non-peak electrical energy
      periods to the greatest extent possible.  See load shedding.
                                   285

-------
precision:  The quality of being exactly defined.  This  is  sometimes
      represented by the number of significant  bits  in  the  digital
      representation.  Also  related to  repeatability instruments.

primary element:  The device which converts  a portion of the  energy of the
      variable to be measured  to a form suitable  for amplification and
      retransmission by other  devices.

priority:  Level of importance of a program  or  device.

priority  interrupt:  The temporary suspension of  a program  currently being
      executed in order to execute a program of higher priority.   Priority
      interrupt functions usually include distinguishing the  highest
      priority interrupt active, remembering lower priority interrupts
      which are active, selectively enabling or disabling priority
      interrupts, executing a  jump instruction  to a  specific  memory
      location, and storing  the program counter register in a specific
      location.

process:  1. The collective  functions performed in and by industrial
      equipment, exclusive of  computer  and/or analog control  and monitoring
      equipment.  2. A general term covering such items  as  assemble,
      compile, generate, interpret and  compute.

process control:  Descriptive  of systems in  which controls  are used for
      automatic regulation of  operations or  processes.

process I/O:  Input and output operations directly associated with a
      process, as contrasted with I/O operations  not associated with the
      process.  For example, in a process control system, analog and digital
      inputs and outputs would be considered process I/O whereas inputs  and
      outputs to bulk storage  would not be process I/O.

process variable:  1. In a control loop, the variable being controlled to
      the setpoint.  2. Any parameter within the  process that is of interest
      from an operations or control standpoint.

programmable controller:  A control machine  using solid-state digital
      logic.  Used primarily for replacement of electromechanical  relay
      panels.

programmable Read Only Memory  (PROM):   A non-volatile (data won't  be lost
      when power is turned off) memory  that  is  used  to store  unchanging
      information such as programs.  The computer system cannot write
      information tc. a PPOM.   PROM's are loaded at the factory and can only
      be  changed using special equipment.

proportional action:  A controller mode which contributes an  output
      proportional to the error.

proportional band:  The range  of the controlled variable that corresponds to
      the full range of the  final control element.
                                   286

-------
protocol:  A set of rules governing  communications between computers that
      insures messages are correctly sent,  received,  and understood.

R/C filter:  An electronic filter  network made  up  of  passive components such
      as resistors and capacitors.

Random Access Memory  (RAM):  Tnat  portion of  computer memory that can be
      both written to and read from.

range:  The region between the limits within  which a  quantity is measured,
      received or transmitted, expressed by stating the lower and upper
      range values.

rate time:  For a linearly changing  input to  a  proportional plus derivative
      mode controller, the time  interval oy which  derivative action advances
      the effect of proportional action.

ratio control:  Control  in which a secondary  input to a process is regulated
      to maintain a preset ratio between the  secondary input and an
      unregulated primary input.

real time:  Tne performance of a computation  during the actual time that the
      related physical process transpires in  order that the results can be
      useful in guiding  the process.

regulatory control:  Maintaining the  outputs  of a  process as closely as
      possible to tneir  respective setpoint values despite the influence of
      setpoint changes and disturbances.

remote:  Referring to an operations point located  at  some distance from the
      field device.              »

remote/local (R/L):  Refers to a switch setting at local panel controls.
      The switch in local position means that control can be exercised at
      the local panel only, locking out control from  a remote location.   The
      switch in remote position  means  that  control is exercised frcm a
      remote location and local  controls are  locked out.

repeataoility:  The ability of an instrument  to produce the same output
      reading when a given condition  is applied repeatedly.

repeats per minute:  Controller  integral mode adjustment units.  The inverse
      of integral time.

reset windup:   In a controller containing integral action,  the saturation ot
      tne controller output at a high or low  limit due to integration of a
      sustained deviation of the controlled variable  from the setpoint.

reverse action controller:  A controller in which  the value  of the output
      signal decreases as the value of the  input (measured  variable)
      increases.
                                  287

-------
screen refresh:  A Hardware function which maintains an  image on  a CRT
      screen by the continuous generation of a composite video  signal from
      data stored in the memory of a CRT controller.

screen update:  A software function which periodically replaces the  dynamic
      data portion of a display with current real-time data.

select-before-operate:  A supervisory control system in  which a point is
      first selected and a return displayed proving the  selection after
      which one of several operations can be performed on  that point.

self-configuring:  A method of programming which eliminates  the need to
      reassemble or recompile programs after a change in configuration by
      the dynamic use of parameters external to the program  which define  the
      particular configuration.

sensor:  See transducer.

sequence control program:  A high-level program whose primary function is to
      cause a sequence of events to happen based on current  process
      requirements or operator requests.

serial transmission:  A mode of transmission whereby bits  of a  data  word  are
      sent sequentially  (starting with either the most or  least significant
      bit) over a single communications channel.

setpoint:  in a control loop, refers to the desired value  of the  process
      variable being controlled.

signal:  1. The event or phenomenon that conveys data from one  point to
      another.  2. A time dependent value attached to a  physical  phenomenon
      and conveying data.

simulation:  The representation of certain features of  the behavior  of a
      physical or abstract system by the behavior of another system, for
      example, the representation of physical phenomena  by means  of
      operations performed by a computer or the representation  of operations
      of a computer by  those of another computer.

software:  1. A set of programs, procedures, rules and  associated
      documentation concerned with the operation of a computer  system, for
      example, compilers, library routines, and manuals.  2. A  program
      package containing instructions for  tne computer  hardware.

software development system:  See development software.

software packages:  Various computer programs or  sets of problems used  in a
      particular application.

software  subsystems:  Refers  to major segments of  the  software  wnich
      performs a unique,  identifiable function.   This  includes  such
       subsystems as operating  system, logging,  scanning, graphic  displays,
      alarming, DDC and  each  separate control function.


                                   288

-------
source code:  Code used as input to a  translation  program,  such as an
      assembler or a compiler.

SCADA:  Supervisory control and data acquisition.

span:  The algebraic difference between  the  upper  and  lower  range values.

steady-state:  A characteristic of a condition,  such as  value,  rate,
      periodicity, or amplitude, exhibiting  only negligible  change over  an
      arbitrary long period of time.   It may describe  a  condition in  which
      some characteristics are static, others dynamic.

supervisory control:  1. A control technique in  which  a  digital computer is
      used to determine and fix setpoints for conventional analog
      controllers.  Used to distinguish  from direct digital  control.   2. A
      high-level program whose primary function  is to  oversee an on-going
      process and alter the general parameters of  a contcol  strategy  based
      upon mathematical relationships.

synchronous transmission:  1. Transmission in which the  sending and
      receiving instruments are operating continuously at substantially  the
      same frequency and are maintained, by  means  of correction,  in a
      desired phase relationship.  2. A  mode of  data transmission whereby
      the message is sent in a continuous bit string.

system regeneration:  The complete reconfiguration of  a  computer's main
      memory and mass memory.  This function will  typically  require talcing
      the computer control subsystem off line.

system software:  Software which includes the operating  system,  resources
      management functions, and processing functions for data acquisition
      and control.

table driven:  A programming method whereby  the  paths  of execution through a
      computer program are controlled by the contents  of a data table
      containing logical or numeric data.

telecommunication:  The use of leased  telephone  lines  for sending
      informative data and performing operational  controls at great
      distances.

telemetering:  The transmission of a measurement over  long distances,
      usually by electromagnetic means.

time constant:  The time required for the output of a  single capacity
      element to change 63.2 percent of  the amount of  total response  when  a
      step change is made in its input.

time slicing:  A technique for allocating CPU time between multiple programs
      within a multi-programming environment.  This technique allocates  a
      given segment of time to each task in a round-t;obin fashion without
      regard to task priority or importance.
                                  289

-------
transducer:  An element or device which receives  information  in the form of
      one ptiysical quantity and converts  it for transmission,  usually in
      analog form.  This is a general definition  and  applies  to specific
      classes of devices such as primary  element,  signal  transducer and
      transmitter.

transmitter:  A transducer which responds to a measured variable by means of
      a sensing element, and converts it  to a standardized  transmission
      signal which is a function only of  the measured variable.

uninterruptible power supply  (UPS):  A power supply having  backup battery
      storage.  A UPS is used to insure operation  of  critical computer
      equipment during power failures.

utility program:  A program providing basic conveniences  such as loading and
      saving programs, and initiating program execution.

watchdog timer:  An electronic internal timer which will  generate a priority
      interrupt unless periodically recycled by a  computer.   It is used to
      detect program stall or hardware failure conditions.

word:  1. A character string or a bit string considered as  an entity.  2. A
      group of binary digits treated as one unit  of information and stored
      in a single memory location.
                                  290

-------
                                  REFERENCES
American National Standards institute.  American National standard  - process
      Instrumentation Terminology.  ANSI/ISA - S51.1.   1979.

American National Standards Institute.  American National Directory for
      Information Processing.  ANSI X3/TR-1-77.

American National Standards Institute.  IEEE Standard Dictionary of
      Electrical and Electronic Terms ANSI/IEEE 100-1977.

SKrolcov, M. R. ED. Mini - and Microcomputer Control in  Industrial
      Processes.  Van Nostrand Reinhold Co.  New York.  1980.

Graf, Rudolf F., Modern Dictionary of Electronics.  Howard W. Sams  & Co.,
      Inc., 1977.
                                      Reproduced from
                                      best available copy.
                                  291

-------