&EPA
United States
Environmental Protection
Agency
Environmental Monitoring and Support EPA-600/4-78-024
Laboratory May 1978
Research Triangle Park NIC 27711
Research and Development
A Technical
Assistance
Document
Use of the Flame
Photometric
Detector Method
for Measurement of
Sulfur Dioxide
in Ambient Air
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-78-024
May 1978
USE OF THE FLAME PHOTOMETRIC DETECTOR METHOD
FOR MEASUREMENT OF SULFUR DIOXIDE IN AMBIENT AIR
A TECHNICAL ASSISTANCE DOCUMENT
by
W. Gary Eaton
Research Triangle Institute
Research Triangle Park, North Carolina 27709
Contract No. 68-02-2433
EPA Project Officer
John H. Margeson
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
Prepared for
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial prod-
ucts does not constitute endorsement or recommendation for use.
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PREFACE
Sulfur dioxide is a pollutant for which national primary and secondary ambient air
quality standards have been established by the Environmental Protection Agency. In
order to insure that the standards (as specified in the Code of Federal Regulations (CFR)
Title 40, Chapter I, Part 50) are not exceeded, continuous monitoring is sometimes
used.
This technical assistance document (TAD) is intended to serve as a sourcebook of in-
formation and outlines of good practices for operation and calibration of S02 analyzers
based on the measurement principle of the flame photometric detection (FPD) method.
Critical parameters are identified which affect the operation and calibration of FPD
analyzers. This document can be used with older analyzers which measure "total"
sulfur, as well as newer models which are improved in specificity for SO2 and have
been designated as "equivalent methods" by EPA.
The reader should note that the techniques for generation of S02 calibration stand-
ards and zero air (discussed in Section 3.0) may be used in conjunction with any am-
bient air SO2 analyzer, not just FPD S02 analyzers.
Many of the items discussed in this document are based on findings from a literature
search, interviews and communications with FPD manufacturers and users, results of
laboratory calibrations and experiments, and trial field use of the document.
This document is to be used by technical personnel in conjunction with the manufac-
turer's instruction manual and the appropriate sections of EPA Quality Assurance
Handbook for Air Pollution Measurement Systems - Volume II (EPA-600/4-77-027a).
This TAD is divided into six major sections: introduction, installation and startup of
an FPD S02 analyzer; generation of S02 calibration standards and zero air; calibration
of the FPD; procedural aids; references and index.
It is recommended that the user of this document first read it entirely and make note
of points which relate to his specific brand of analyzer. Index tabs can be attached to
pages of special interest so they can be found again quickly. Note that precautionary or
emphasized material in this document is set apart from the text by being enclosed in
"boxes."
The user's attention is called particularly to the following topics covered in this docu-
ment:
Topic Section
Nonequivalent FPD analyzers 1.3.3
Temperature and humidity control 2.2.2
Ambient air sampling 2.2.4
Safe use of hydrogen 2.3.3, 2.3.4
Generation of calibration standards and 3.0
zero air
Carbon dioxide interferences 3.6.3
Zero, span, and multipoint calibration 4.0
Airflow measurements and corrections 5.0
iii
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IV
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ACKNOWLEDGMENTS
This document was written under Contract No. 68-02-2433 for the Environmental
Protection Agency. The support of this agency is gratefully acknowledged as is the ad-
vice and guidance of the Project Officer, John H. Margeson.
Laboratory studies and preparation of this document were carried out in the Systems
and Measurements Division of RTI under the general direction of Mr. J. J. B. Worth,
Group III Vice President, and Mr. J. B. Tommerdahl, Division Director. Mr. C. E. Decker,
Manager, Environmental Measurements Department, was Laboratory Supervisor for
this contract. RTI staff members G. Maier, E. Pedudo, F. Smith, D. Strait and R. Wright
reviewed the document and made many helpful suggestions. Messrs. R. Denyszyn, F.
Dimmock, and L. Hackworth each aided in the laboratory trials and experiments.
Special acknowledgment is made to Messrs. R. Baumgardner, F, McElroy, F. Smith,
and D. vonLehmden, members of EPA's Environmental Monitoring and Support
Laboratory, for their advice and critical review of the document. Dr. M. Cher; Mr. D.
Brittain, EPA Region IV; and Mr. B. Towns, EPA Region X are also acknowledged.
Grateful appreciation is also extended to representatives of manufacturers of
analyzers, calibration equipment, permeation devices, and specialty gases who were
most cooperative in discussing many topics in the document and reviewing the
manuscript itself. Included in this group are Mr. C. Laird of the Bendix Corporation,
Dr. Q. Stahel of Meloy Laboratories, Inc., and Mr. D. Lucero of Monitor Labs, Inc.
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VI
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ABSTRACT
This Technical Assistance Document is intended to serve as a source-book of infor-
mation and outlines of good practice for operation and calibration of ambient air SO2
detection analyzers based on the measurement principle of Flame Photometric Detec-
tion (FPD). This is accomplished through the identification and control of critical
parameters affecting the operation and calibration of FPD analyzers. The document
may be used with analyzers which measure total sulfur, as well as with new S02-
specific models which have been designated as equivalent methods by EPA,
This document is to be used in conjunction with the instrument manufacturer's in-
struction manual. The document consists of six sections: (1) Introduction to FPD prin-
ciple, (2) Installation and startup of the analyzer, (3) Calibration sources and their air
supplies, (4) Procedures for multipoint dynamic calibration, (5) Procedural aids, and (6)
References and Index.
This report was submitted in fulfillment of Contract No. 68-02-2433 by Research
Triangle Institute under the sponsorship of the Environmental Protection Agency.
VII
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VIII
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CONTENTS
Preface r iii
Acknowledgments v
Abstract vii
Figures xiii
Tables xv
Section 1.0 - Introduction 1
1.1 Flame Photometric Detection of Sulfur: Basic Principles . . 1
1.2 Application of FPD to Continuous Detection of S02 in
Ambient Air 4
1.2.1 Background: Principles of Operation 4
1.3 Commercially Available FPD Ambient Air S02 Analyzers .... 8
1.3.1 Manufacturers and Their Instruments 8
1.3.2 Compliance Monitoring-Reference and
Equivalent Methods 9
1.3.3 Recommendations for Use of Nonequivalent
FPD Sulfur Analyzers 10
1.4 Calibration Gas Delivery System: Sources of S02 ....... . .......... .14
1.5 Recordkeeping, Maintenance, and Quality Control 14
Section 2.0 - Installation and Startup of the FPD S02 Analyzer .... 17
2.1 Introduction 17
2.2 Requirements of the Facility Which Houses the Analyzer ... 17
2.2.1 Electrical Requirements 18
2.2.2 Temperature and Humidity Control Requirements .... 18
2.2.3 Spatial Requirements 20
2.2.4 Ambient Air Sampling Requirements ... 20
2.3 Installation of an FPD S02 Analyzer 22
2.3.1 Unpacking the Analyzer 22
2.3.2 Electrical and Pneumatic Connections 22
2.3.3 Guidelines for the Safe Use of Hydrogen Cylinders . . 26
2.3.4 Procedures and Safety Precautions for Use of
Electrolytic Hydrogen Generators . . 29
2.4 Startup of an FPD S02 Analyzer 31
2.4.1 Power On; Warmup Times 31
2.4.2 "Peaking Up" Response Prior to Calibration 32
Section 3.0 - Generation of S02 Calibration Standards and Zero Air . . 35
3.1 Introduction 35
3.2 Clean Air Sources for S02 Calibration Systems 36
3.2.1 Zero Air Generators 36
3.2.2 Compressed Air Cylinders . 39
IX
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3.3 Permeation Tubes and Devices Containing Liquefied
S02: Characteristics and Use 39
3.3.1 Introduction '•'-'.'.'.'.'.'.'.'.'. 39
3.3.2 Description of NBS Permeation Tubes ......... 40
3.4 Calibration Systems Based on Permeation Devices:
Description and Explanation of Use 45
3.4.1 Custom-built Laboratory Systems Employing
Permeation Tubes 45
3.4.2 Commercial Systems Employing Permeation Tubes
or Devices 49
3.4.3 Explanation of Use of Permeation Device
Calibration Systems 54
3.4.4 Computation of S02 Concentrations From
Permeation Tubes 58
3.5 Calibration by Use of Compressed Gas Cylinders
Containing S02 in Nitrogen or Air 60
3.5.1 General 60
3.5.2 Equipment Specifications and Use 61
3.5.3 Guidelines for Use of S02 Dilution Systems 65
3.6 Other Factors Affecting the S02 Output From Dynamic
Calibration Systems and/or the Response of FPD S02
Analyzers 67
3.6.1 Temperature at Which the Permeation Tube is Used ... 67
3.6.2 Air Flow Rate and Clean Air Supply 67
3.6.3 Carbon Dioxide Interference in the FPD
Method for Sulfur Dioxide 68
3.6.4 Percentage of Oxygen in Calibration Air 72
3.7 Summary of FPD S02 Calibration Source Parameters Which
Must be Operator-Controlled 73
Section 4.0 - Calibration of the Flame Photometric Detector for
S02 in Ambient Air 81
4.1 Introduction to Calibration 81
4-1.1 Qualitative and Quantitative Analyses 81
4.1.2 Definition of Calibration; Requirements for
Calibration 82
4.1.3 Recordkeeping 83
4.2 Preliminary Steps . . 84
4.3 Zero and Span Check ' ' ' g^
4.4 Maintenance and Replacement Operations 95
4.5 Multipoint Calibration of an FPD S02 Analyzer Equipped
with a Linearized Output gg
4.6 Supplementary Instructions for Particular FPD Analyzers 113
4-6.1 Bendix Model 8300: Electronic Zero and '
Operational Zero -,-,0
4.6.2 Use of the Optional Log-Linear Output of Meioy
FPD Analyzers 115
4.6.3 Data Correction Due to Baseline Offset of the
Meloy Lab's Model SA 185 Output 118
4.7 Summary of FPD Analyzer Parameters Which Must Be
Operator-Controlled
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Section 5.0 - Procedural Aids 131
5.1 Introduction 131
5.2 Soap Film Flowmeter, SFFM, or Bubble Flowmeter 132
5.3 Mercury Column Barometer, Fortin Type 136
5.4 Water Manometer, U-Tube 139
5.5 Steps for Correcting Airflow to Standard Temperature and
Pressure^ 141
5.6 Ascarite Method for C02 Determination 141
5.6.1 Procedure 143
References 145
Index 147
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FIGURES
Number Page
1.1 S2 emission bands observed in a shielded air-hydrogen flame ... 3
1.2 Gas flow diagram of continuous flame photometric detector
for S02 in ambient air 5
1.3 Flame photometric detector (FPD) sulfur response
characteristics (Monitor Labs FPD) 7
2.1 Detailed views of various ways for connecting 1/8 in. o.d. Teflon
sampling lines to manifold 21
2.2 Typical installation of FPD S02 analyzer 23
2.3 Hydrogen regulator assembly and CGA cylinder connector #350 ... 27
3.1 Zero air generator suitable for FPD S02 zero and calibration ... 37
3.2 National Bureau of Standards standard reference material
S02 permeation tube 41
3.3 National Bureau of Standards sulfur dioxide permeation
tube certificate 42
3.4 Example of custom made laboratory permeation tube assembly for
calibration of S02 analyzers ..... 46
3.5 Laboratory clean air supply 47
3.6 Schematic diagram of a portable S02 calibrator with internal
air supply 50
3.7 Schematic diagram of multipollutant calibrator 51
3.8 Concentration of S02 versus time. Low-level S02 in air;
treated aluminum cylinder 62
3.9 Assembly for dilution of S02 from cylinder of S02
for use in calibration or span check 64
3.10 Variation of FPD analyzer response with air oxygen
content at a fixed S02 concentration of 0.0806 ppm 74
4.1 Sampling line filter holder and filter of all-Teflon
construction 97
4.2 Calibration trace of linearized output. FPD ambient air
S02 analyzer 101
4.3 Calibration curve for linearized FPD S02 analyzer 110
4.4 Log-log output of the Meloy Mode] SA 185 FPD S02 analyzer .... 116
4.5 Log-linear plot of calibration data, Meloy Model SA 185-2A
FPD S02 analyzer 117
5.1 Soap film flowmeter 133
5.2 Water manometer, "U" tube 140
5.3 Ascarite sampling train for C02 determination 144
xn i
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XIV
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TABLES
Number
1.1 Performance specifications for automated methods for S02 11
3.1 Certified permeation rates for National Bureau of Standards
permeation tube No. 33-64 44
3.2 Typical errors due to temperature variation of an S02
permeation tube 68
3.3 Evaluation of C02 interference in total sulfur measurements
using FPD analyzers 70
3.4 FPD analyzer response, ppm S02, in the presence and
absence of carbon dioxide 71
3.5 Retention of C02 on commonly employed scrubber materials 73
3.6 S02 calibration source parameters which must be operator-
controlled in order to obtain valid data 76
4.1 Barometric pressure at various altitudes 92
4.2 Typical effect of an offset of 0.065 V (0.01 ppm) 120
4.3 Typical effect of an offset of 0.147 V (0.015 ppm) . . 121
4.4 FPD analyzer parameters which must be operator-
controlled in order to obtain valid data 122
5.1 Vapor pressure of water at various temperatures, mm Hg 142
xv
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XVI
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SECTION 1.0
INTRODUCTION
1.1 FLAME PHOTOMETRIC DETECTION OF SULFUR: BASIC PRINCIPLES
Many elements give characteristic emission spectra when burned in a
flame. Absorption of energy from the flame allows a ground-state atom or
molecule to reach a higher energy level or an excited state. The excited-
state atom or molecule contains excess energy and may return to its ground
state by emitting light. The wavelength and intensity of this light are the
basis for selective and quantitative analysis of different elements or com-
pounds.
When a sulfur-containing compound (inorganic or organic) is burned in a
flame, a minor product is the excited-state diatomic molecular sulfur spe-
cies, S2*. The asterisk (*) indicates the species is excited, that is, has
energy in excess of that of the unexcited, ground-state, S2 species. The
S2* species is inclined to seek a lower energy level and one mechanism by
which S2* reverts to its ground state is by a chemiluminescent process. By
this process light energy is emitted with the spectral characteristics shown
in Figure l.l.1'2'3 Two equations describing this are:
sulfur-containing molecules ^. S2* (1)
in flame
S2* + S2 + light, hv (2)
(excited electronic state) (normal electronic state)
The left-hand side of equation 2 shows the excited state S2* species.
The right-hand side shows the products of the decomposition of S2*. The
products are the unexcited S2 species and a quantity of light energy, i.e.,
photons (hence the name "photometric" detector). The "detector" portion of
the flame photometric detector is a photomultiplier tube, which senses the
light energy emission intensity and converts it to an equivalent electrical
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current which is proportional to the original concentration of S02 (or other
sulfur-containing gas) in the air sample.
The S2 emission system is broad-based and falls mainly in the region
2,769 to 6,166 A. Figure 1.1 shows a portion of the emission spectrum. The
peak of the spectrum is around 380 nm (3,840 A). Narrow-band pass filters
are commonly used in detector assemblies to allow only light near the peak
region to pass.
The formation of the S2 molecule in the flame occurs when two S atoms
combine in the presence of a "third body" (denoted by M), equation 3:
S + S + M S2 + M. (3)
Hydrogen and hydroxyl radicals, also produced by the flame, react with
S2 to produce the excited state S2* species4'5'6 (equations 4,5).
H + H + S2 S2* + H2 (4)
OH + H + S2 S2* + H20 (5)
The intensity of the chemi luminescence or light produced by S2* as
described by equation 2 is proportional to the S2* concentration, [S2*],
equation 6:
light intensity = k [S2*]. (6)
As stated above, formation of S2 depends on reaction between two S
atoms in the presence of a third body, M (another gaseous atom or molecule).
For reaction to occur, the two S atoms must collide simultaneously with M.
It can be shown that the number of collisions (and therefore potential
reactions between two sulfur atoms) is proportional to the square of their
concentration. 7
Therefore the rate of formation of the S2* molecular species will be
proportional to the square of the S atom concentration, equation 7, which in
turn depends on the concentration of the sulfur-containing molecule.
Thus, for a continuous S02 analyzer based on flame photometry, the
light energy produced by decaying S2* and received by the photomultiplier
tube is predicted to be proportional to the square of the S02 concentration
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384
374
364
C/3
yt
LU
<
_l
LU
CC
355
350
394
405
415
427
WAVELENGTH, nm
Figure 1.1. 82 emission bands observed in a shielded air-hydrogen flame.
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The exact theoretical exponential factor of 2 is not usually found.
Instead, a lower value is found. This diminishment is caused by variation
in flame conditions and by self-collisional quenching processes without
chemiluminescence.
1.2 APPLICATION OF FPD TO CONTINUOUS DETECTION OF S02 IN AMBIENT AIR
1.2.1 Background: Principles of Operation
Application of the flame photometric technique to measure sulfur gases
in air was first disclosed in a German patent issued to Draegerwerk and
Drager.8 Crider9 in 1965 and Brody and Chaney10 in 1966 further optimized
the FPD technique for analysis of a variety of sulfur-containing compounds.
Ambient air FPD S02 analyzers are designed to supply a sample of air
continuously to the flame photometric detector. The air sample serves as
the source of oxygen to support the combustion of the hydrogen fuel and to
maintain the flame. To achieve sensitivity, stability, and selectivity, the
continuous analyzer must possess certain pneumatic, electronic, and physical
features.11
Figure 1.2 illustrates the gas flow pathways of a typical continuous
FPD analyzer for S02 in ambient air. A vented evacuation pump, located
downstream of the burner, pulls the air sample or calibration gas into the
analyzer through TeflonT tubing. The sample passes through a 5-micron pore
size Teflon particulate filter (caution: use only the manufacturer's spec-
ified filter arrangement), a rotameter, a three-way solenoid valve, an
optional H2S scrubber assembly,12 and finally enters the burner block where
it combines with hydrogen and supports the flame. The sample rotameter is
used only when flows are checked; normally it is bypassed by use of the
solenoid valve. The H2S scrubber is a required item on EPA-designated
"equivalent method" units. It removes H2S and allows S02 to pass. This
improves the specificity of the analyzer. Without the scrubber, the unit is
a "total sulfur" analyzer and responds to almost all sulfur compounds that
reach the flame.
The fuel, hydrogen, enters through stainless steel tubing from a pres-
surized source. It first passes through a solenoid valve (which will close
Co.
^"Teflon" is a registered trademark of E.I. Du Pont de Nemours &
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ADJUSTABLE NEEDLE
VALVE OR LIMITING
ORIFICE
PARTICULATE FILTER
(-100 MICRON)
EVACUATION PUMP
VENT
f I-
DILUTION AIR IN
H2GAUGE
0 60 PSIG
FLAME PHOTOMETRIC
DETECTOR ASSEMBLY
SHUT-OFF
SOLENOID VALVE (H2)
HYDROGEN IN
en
H2SSCRUBBER
ASSEMBLY EPA
DESIGNATED EQUI
VALENT UNITS
ONLY
HYDROGEN
ROTAMETER
HYDROGEN
PRESSURE
REGULATOR
TFE SAMPLE
SOLENOID VALVE
SAMPLE
ROTAMETER
I—I
5 MICRON TEFLON
PARTICULATE FILTER
AIR SAMPLE OR
CALIBRATION
GAS IN
Figure 1.2. Gas flow diagram of continuous flame photometric detector
for S02 in ambient air.
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automatically if the flame should go out, thus preventing a hazardous build-
up of hydrogen), then through a pressure regulator and gauge, through a
flow-indicating rotameter, and then through a flow-1imiting plug or capil-
lary tube to the burner. To achieve a steady flow of hydrogen, the plug or
capillary is usually located within an oven, where it is maintained at a
constant temperature.
The third flow of gas is dilution air. Room air is pulled into the
analyzer by the evacuation pump. It first passes through a particulate
filter, then through an adjustable needle valve or limiting orifice, and
finally meets and dilutes the vapors that are being pulled from the flame
chamber. This dilution prevents condensation of unwanted water vapor and
corrosive products from the flame.
The flame photometric detector itself is housed in a temperature-
controlled cell. It is made up of three functional subsystems: the burner
or flame holder, the flame chamber, and the photomultiplier tube. Air
carrying sulfur-containing molecules enters through the bottom of the
burner. The burner provides a support for the flame. The flame is sur-
rounded by hydrogen, which is enclosed by the flame chamber. This arrange-
ment produces a cool hydrogen-air flame, which is well-suited for the forma-
tion of the S2* molecular species. It is a hydrogen hyperventilated dif-
fusion flame. One wall of the flame chamber is a clear optical window and
narrow bandpass optical filter through which the photomultiplier tube (PMT)
measures the light emission intensity from the S2* species at wavelengths
near 394 nm and converts it to an equivalent electrical current. The PMT is
temperature controlled. A regulated high-voltage power supply stabilizes
the PMT output.
The output current of the PMT is approximately proportional to the
square (the 2nd power) of the concentration of the sulfur present in the
sample.13
response ~ (sulfur atom concentration)2
The actual exponential value is generally somewhat less than 2, usually
between 1.7 and 1.9. Figure 1.3 illustrates the chemiluminescent S * emis-
sion intensity - sulfur concentration relationship for the 400-380 nm (4 000-
3,800 A) region. Note that the PMT currents and sulfur dioxide concentr -
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1,000
s 100 _
O
X
10-
DETECTOR RESPONSE FACTOR (n) -1.86
I
n-B
n-7
n-6
,0-10 10-9 10-° ID'7 10"° 10
CHEMILUMINESCENT S2 EMISSION INTENSITY EXPRESSED AS PHOTOMULTIPLIER TUBE OUTPUT CURRENT, AMPS
,-B
Figure 1.3. Flame photometric detector (FPD) sulfur response characteristics
(Monitor Labs FPD).
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tions are plotted on a log-log graph. Note that the slope of the line is
1.86, fairly near the theoretical slope of 2.00. Beyond concentrations of
about 1 ppm, the S2* species returns to its ground state without chemi-
luminescense by a self-collisional quenching process. At sulfur dioxide
levels of 1 ppm and higher, the FPD signal current begins to deviate from
the square relationship and the slope of the line in Figure 1.3 increases
rapidly. In other words, the response of the analyzer does not change much
as the sulfur dioxide concentration increases.
The log-log output form of Figure 1.3 is seldom used with ambient air
analyzers. Instead the signal is treated electronically such that a linear-
ized signal is obtained. This enables a linear relation between analyzer
response (e.g., output volts) and sulfur dioxide concentration (ppm) to be
plotted on linear graph paper. See Figure 4-3 for an example of such a
plot.
1.3 COMMERCIALLY AVAILABLE FPD AMBIENT AIR S02 ANALYZERS
1.3.1 Manufacturers and Their Instruments
At the present time (1978) there are three major U.S. manufacturers of
continuous-type FPD analyzers for total sulfur and/or sulfur dioxide in
ambient air. These are:
1. The Bendix Corporation, Environmental and Process Instruments
Division, Drawer 831, Lewisburg, WV 24901
2. Meloy Laboratories, Incorporated, 6715 Electronic Drive, Spring-
field, VA 22151
3. Monitor Labs, Incorporated, 4202 Sorrento Valley Blvd., San Diego,
CA 92121
A fourth manufacturer, Tracer, Incorporated, 6500 Tracer Lane, Austin
TX 78721, offers a gas chromatography-flame photometry analyzer, which
separates sulfur compounds prior to FPD detection. A "total sulfur" mode is
also available wherein the sample bypasses the column and goes directly to
the FPD.
Performance, operational, and configurational specifications are avail-
able from each manufacturer on a full line of FPD analyzers and options
Each of the manufacturers of continuous analyzers has one or more analv
which has been designated as an "equivalent method" by EPA or i<= a r. ^-j /
«• is a candidate
8
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for designation. This designation is discussed in Section 1.3.2. Such
designation means only that the analyzer meets certain minimum standards.
Competitive differences exist between FPD analyzers. Thus, the need for a
careful selection process based on the individual air-monitoring situation
is very important.
Indeed, if new S02 ambient air monitoring equipment is to be purchased,
consideration should also be given to other methods of S02 detection that
have been designated as equivalent methods or are candidates for designa-
tion. Such measurement methods include amperometric analyzers (Phillips
Instruments, Incorporated), second derivative spectroscopy (Lear-Siegler
Corporation), and pulsed UV fluorescence analysis (Thermo-Electron Corpora-
tion and Beckman Instrument Corporation).
1.3.2 Compliance Monitoring-Reference and Equivalent Methods
Certain air pollution control agencies, such as State agencies, are
required to monitor the ambient air to determine compliance with National
Ambient Air Quality Standards. The standards are given in Title 40, Chapter
1, Part 50 of the Code of Federal Regulations. Specific monitoring require-
ments are given in Part 51. An amendment to Part 51 was issued on February
18, 1975 (40 CFR 7043), and requires that for purposes of compliance monitor-
ing "each method for measuring S02, CO, or photochemical oxidant . . . shall
be a reference method or equivalent method ..." An exception to this
requirement allows automated analyzers purchased prior to February 18, 1976,
to be used until February 18, 1980.
The definitions and qualifications of reference and equivalent methods
are given in 40 CFR Part 53. For S02, the reference method is a manual
method and is completely specified in Appendix A of 40 CFR Part 50. Thus,
all other methods for S02 compliance measurement must be designated as
equivalent methods by EPA. A notice of each method designated as equivalent
is published in the Federal Register. A current list of all designated
reference and equivalent methods is maintained by EPA and may be obtained
f
from EPA Regional Offices or from the Environmental Monitoring and Support
Laboratory, Department E, MD-76, Research Triangle Park, NC 27711.
Sellers of designated methods for sulfur dioxide must comply with
certain conditions, one of which is that the analyzer must function within
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the limits of the performance specifications given in Table 1.1 for at least
1 year after delivery when maintained and operated in accordance with the
operation manual. Aside from occasional breakdowns or malfunctions, consist-
ent or repeated noncompliance with any of these specificatons should be
reported to EPA at the address given previously.
For automated methods, a designation applies to any analyzer that is
identical to the analyzer described in the designation. In many cases,
analyzers manufactured prior to the designation may be upgraded (e.g., by
minor modification or by substitution of a new operation or instruction
manual) so as to be identical to the designated method and thus achieve
designated status at a modest cost. The manufacturer should be consulted to
determine the feasibility of such upgrading. Any modification to a refer-
ence or equivalent method made by a user must be approved by EPA if the
designated status is to be maintained.
1.3.3 Recommendations for Use of Nonequivalent FPD Sulfur Analyzers
As was mentioned in the last section, older FPD analyzers may be up-
graded and, thus, achieve designated status at modest cost. Any modifi-
cations should be done after consultation with the manufacturer and obtain-
ing EPA approval.
This section contains recommendations for modifications and procedural
changes to make older FPD sulfur analyzers more sensitive and more specific
for S02. It must be emphasized that making these modifications yourself
does not make your analyzer an equivalent method. However, for noncom-
pliance monitoring and until such time as an equivalency-designated instru-
ment is necessary, these steps should help give better data.
Replace all sampling lines. All sampling lines leading from the moni-
toring station ambient air manifold to the rear of the analyzer should be
cleaned or replaced entirely with new cleaned Teflon tubing. This mainte-
nance is necessary because the S02 in the sample can be adsorbed or reduced
chemically be dirt, oil, and other debris on the tube wall. Frequency of
tubing replacement should be determined by visual inspection of the line.
Any fittings which are made of metal or plastic and come into contact with
the sample should be either replaced with Teflon fittings or bored out so
the Teflon tube passes continuously through the fitting. Tubing inside the
10
-------
Table 1.1. Performance specifications for automated methods for S02
Performance parameter
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Caen i nueryerenu — — —-_—-— —
luuai interierent ——__-— — .
limit
OUA> OT upper range
limit
Lag time
limit
80% of upper range
limit
Units!
.
do
____/-i,-,___________
___.4.->__ ___ _
do
do
_H/\-_— _
~ao
.
Parts per million
do
Sulfur
dioxide
0-0.5
0.005
0.01
±0.02
0.06
±0.02
±20.0
± 5.0
20
15
15
0.01
0.015
Definitions
and test
procedures
§53.23(a).
§53.23(b).
§53.23(c).
__ ££."} O'ifri}
SDJ. £3{Q).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
_ 0 CO OO f r\ "\
s^-j- ^ov.ej.
Table 1.1 is reproduced from a portion of Table B-l of CFR 40 Part 53.
fTo convert from parts per million to micrograms per cubic meter at 25° C and 760 mm Hg, multiply by
M/0.02447, where M is the molecular weight of the gas: M = 64 for SO,
-------
analyzer that leads to air flow rotameters and to the burner block should
also be removed and replaced. The sample should not pass through the rotam-
eter during normal sample monitoring operations since S02 gas is removed by
the rotameter components; it should bypass the rotameter. Any solenoid
valves which are in the sample line should have Teflon interiors and should
be cleaned or replaced if dirty. A Teflon holder with membrane filter, such
as the "Mace" filter (available from the Mace Corporation, S. El Monte, CA
91733), mounted in the sampling line will minimize particulate accumulation.
Clean burner block and "window." The burner block of most FPD analyz-
ers can be removed and disassembled. Accumulated dust and corrosion are
removed (use fine steel wool) and the surfaces and fittings are cleaned with
mild soap and water. It is advisable to replace any "0" rings with new ones
at this time. Use only the manufacturer's recommended "0" rings since
others may tend to cold-flow or otherwise lose their sealing properties.
For example, the Me Toy model SA-285 requires Viton "0" rings. Next, rinse
the parts with deionized water and then allow them to dry. It may be nec-
essary to replace the thermocouple sensor and the ignitor wire or glowplug
at this time. If the thermocouple is removed or replaced, be sure it is
re-installed identically to the original thermocouple. If the polarity of
the leads is reversed, the circuitry controlling the H2 solenoid may actuate
and stop the hydrogen flow, giving a flame-out. Also check the operability
of burner block heating elements and replace them if necessary. Between the
flame and the photomultiplier tube are a clear "window" and a 394 ± 20 nm
optical filter. Examine each for cloudiness, staining, or pitting, and
clean or replace them as necessary. This will allow more light to reach the
PM tube. Some manufacturers suggest that the burner block be flushed with
certain solvents and then dried. This procedure is outlined in the manu-
facturer's instruction manual and may be used.
Overhaul or replace sample pump. If the analyzer contains a pump, it
is probably a small bellows pump or diaphragm pump. Over long periods of
use, these pumps develop problems in the diaphragm area (due to dust and
general fatigue), and variable flows result. Replace any worn parts and
reseal the pump properly. A new valve assembly may be required for bellows
pumps. Consult the pump manufacturer's maintenance instructions regarding
allowable vacuum pressure and flow rate limits. If an external pump is
12
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used, be sure it is of sufficient capacity to do the job and that it oper-
ates smoothly.
Install filter on dilution air entry. Older models may not have par-
ti cul ate filters on the dilution air entry at the rear of the analyzer. To
minimize particle and dust entrainment, which might alter the dilution flow
rate, install a simple in-line filter. The filter should pass air easily so
that adequate flow is maintained. Porous paper filters mounted in small
plastic holders work well.
Install H2S scrubber. The H2S scrubber is an item which seldom accom-
panied older FPD analyzers since they were designed as "total sulfur" moni-
tors. Today, each of the three major FPD analyzer manufacturers provides
separate H2S scrubbers, which can be purchased and installed on older ana-
lyzers. These scrubbers remove H2S but allow S02 to pass unaffected.
Clean or replace and recalibrate rotameters. Most analyzers have
hydrogen fuel and air sample rotameters to indicate flow rates. After long
usage, these rotameters may become dirty and dusty and require disassembly
and cleaning. Methanol is suggested as a cleaning solvent. Use it in a
ventilated area since methanol is toxic. After drying and reassembly, the
rotameter should be calibrated (or the certified calibration curve, which
accompanied the rotameter, should be verified) by comparison to a certified
soap film flowmeter, spirometer, or wet test meter. For normal ambient air
monitoring, the air sample should bypass the rotameter and flow directly to
the flame compartment.
Electronic checks. If there is reason to suspect that the electronics
need repair or coarse adjustment, a qualified electronic technician or
service representative should examine and test the analyzer. Adjustments
may be made prior to the calibration procedure.
Calibration procedure. Some users of older FPD analyzers may be accus-
tomed to calibrating an analyzer by simply "zeroing" and "spanning" the ana-
lyzer. This practice is discouraged.
To operate an analyzer designated as an "equivalent method," a more
detailed monthly calibration, which includes a zero point, span point, and
three or more intermediate concentration points, is initially recommended.
If possible, one or more of the calibration points should be representative
of the concentration levels that are actually being experienced in the
13
-------
ambient air. Use of multiple calibration points shows the linearity (or
lack of linearity) of the analyzer's response. A lack of linearity can be
corrected by adjustment of the linearization circuitry as specified by the
manufacturer. The use of graphical display of calibration data and least
squares regression equation computations are suggested. Details for carry-
ing out such a calibration are given in Section 4.0 of this document.
1.4 CALIBRATION GAS DELIVERY SYSTEM: SOURCES OF S02
A reliable and accurate system of delivering known concentrations of
S02 calibration gas to the FPD analyzer is a necessity. Several commercial
systems are available. They usually employ permeation tubes or devices as
S02 sources. The temperature of the tube or device is controlled by use of
a thermostatted water or air bath or other method. Calibrators may also be
fabricated by the user. Desirable characteristics of dynamic S02 calibra-
tors and general instructions for their use are given in Section 3.0 of this
document.
The source of S02 should be an NBS-certified permeation tube or another
tube or device whose permeation rate is traceable to an NBS Standard Refer-
ence Material tube. Sources of air for dilution of permeation tube effluent
are also discussed in Section 3.0. Particular attention should be given to
both the C02 and 02 content of diluent air. The use of S02 in air from
compressed gas cylinders is also discussed in Section 3.0.
1.5 RECORDKEEPING, MAINTENANCE, AND QUALITY CONTROL
Proper recording of all data from calibrations, zero and span checks,
etc., is essential to overall data quality. This document does not give a
format for data recording, but does emphasize when data should be recorded.
Preventive maintenance and major maintenance items are only noted in
this document. The user should refer to the analyzer's instruction manual
for details of maintenance and troubleshooting procedures.
Quality control and quality assurance are most important to insure
production of good data. A major aspect of quality control is calibration.
This is treated thoroughly in this document. For other aspects of quality
control and assurance, the reader is referred to the EPA publications
"Quality Assurance Handbook for Air Pollution Measurement Systems, Volume I,
14
-------
Principles" (EPA-600/9-76-005, March, 1976) and "Quality Assurance Handbook
for Air Pollution Measurement Systems, Volume II, Ambient Air Specific
Methods" (EPA-600/4-77-027a, May, 1977).
15
-------
16
-------
SECTION 2.0
INSTALLATION AND STARTUP OF THE FPD S02 ANALYZER
2.1 INTRODUCTION
Correct installation and startup of an FPD S02 analyzer is the first
step of an ambient air monitoring program for S02- In addition to a well-
equipped tool box, brass, stainless steel and Teflon tubing, compression
fittings, signal cable, hydrogen fuel, and a hydrogen regulator will be
required. Flow-measuring devices such as a selection of rotameters and a
soap film flowmeter are necessary. A wet test meter and a mass flowmeter
are useful, especially in the laboratory. A stopwatch, hand calculator, and
a recorder or digital voltmeter will also be required.
If the analyzer is to be installed and used in a laboratory, the neces-
sary equipment for calibration, etc., will generally be available. If the
analyzer is to be installed at a field station (unattended operation), it is
recommended that the analyzer first be unpacked, checked, set up, cali-
brated, and operated for several days at the central laboratory. This
procedure will contribute to better understanding of the analyzer and will
demonstrate its proper calibration and operation before field usage. The
analyzer is then taken to the field site, installed, and calibrated.
VERY IMPORTANT: before beginning any installation procedures,
first read the manufacturer's operation and maintenance
manual for your FPD analyzer. Become familiar with the lo-
cation and function of all controls and gas and electrical
connections. If the original manual is lost or misplaced,
order a replacement.
2.2 REQUIREMENTS OF THE FACILITY WHICH HOUSES THE ANALYZER
The room, trailer, or shelter which houses the analyzer will probably
also house other ambient air monitors, calibration systems, meteorological
17
-------
systems, strip chart recorders, and perhaps a magnetic tape data acquisition
system.
The physical facility housing the FPD analyzer should meet certain
requirements so that optimum analyzer performance is obtained.
2.2.1 Electrical Requirements
Note: before connecting any power to your FPD analyzer, be
certain that all switches for power, pump, etc., are in the
OFF position. Unusual power surges have been known to cause
damage to photomultiplier tubes and other analyzer components.
Commercial instruments operate over the voltage range 105-125 on 60 Hz,
single phase power. Be sure there are no voltage fluctuations in the line.
If such fluctuations are suspected, the power company can detect and perhaps
correct the problem. Power requirements vary from 250 to 500 W. For rea-
sons of safety (prevention of electrical shock), proper operation of the
analyzer, and warranty requirements, it is essential that adequate power be
present for the monitoring site and that power be supplied to the analyzer
through the conventionally grounded 3-pin power plug supplied with the
analyzer. This ground must not be defeated by cutting off the round pin on
the power cable. If the instrument must be operated from the two-contact
outlet, grounding is preserved by using a three-conductor to two-conductor
adapter and connecting the adapter wire to a suitable ground such as a cold
water pipe or a grounding rod (embedded in soil). The use of extension
cords is not recommended unless they are of the heavy duty type.
2.2.2 Temperature and Humidity Control Requirements
Each of the commercially available instruments is designed to operate
(with minimal effect on instrument drift) over the temperature range 20° -
30° C (74° - 86° F) and over the range 10° - 40° C with possibly signifi-
cant degradation in the noise, precision, and drift specifications
Other ambient air monitors will have similar temperature range require-
ments. The best environment is an air-conditioned/heated room with a ther-
mostat that maintains the room temperature somewhere in the range 20°
30° C. A temperature of 25° C (77° F) is ideal since this is the "standard"
temperature for air sampling. If the instrument is rack-mounted, it is
18
-------
important that the rack enclosure be properly ventilated. The temperature
inside enclosed relay racks which are not ventilated may be as much as 15° -
25° C above laboratory ambient temperatures.
One must be careful not to let the temperature inside the laboratory or
sampling site facility fall too low, as this can cause water from the moist
ambient air to condense in the station air sampling manifold and possibly
condense in the sampling lines leading to the instruments. This will cause
removal of S02. Deflect the cold air from air conditioners or relocate the
air conditioner away from the manifolds and sampling lines. If condensation
problems persist, it may be necessary to insulate and slightly heat the
station sampling manifold and instrument sampling line.
All of the above variations in temperature may cause the instrument to
respond in an erratic, drifting, manner, due to temperature changes across
the burner block assembly.
Another note on temperature effects concerns the exhaust or vent line
from the flame photometric detector. Since hydrogen is being burned in the
flame chamber, water is produced and exhausted from the instrument. Dilu-
tion air mixes with the water-laden hot exhaust gases to reduce the amount
of water per volume of air to a point below the dew point at normal room
temperatures. If the temperature of the facility is low enough to cause
condensation of this water, a "plug" of water may form in the vent line.
This will cause the sample flow of the analyzer to vary since both dilution
air and sample air are pulled in with the same pump and disturbance of one
flow affects the other. To avoid this, a 6.4 mm (0.25 in.) o.d. exhaust
line (polyethylene is acceptable) should be installed in such a way that
drainage of water always occurs and no points exist where water can stand in
the line.
The exhaust line should be vented to a point outside the building or to
a vent system whose ultimate exit is well away from the sample inlet source
and occupied enclosed areas. In this way excess hydrogen will be safely
vented to the ambient air if the instrument's flame is extinguished and the
instrument has no hydrogen solenoid shutoff or the solenoid fails. The
length of the exhaust line should be minimal. If the length is changed it
should be done just prior to a multipoint calibration. If the exhaust line
leads to the outside ambient air, proper drainage should be maintained
19
-------
outside, too. Extremely cold weather may cause condensation and freezing of
water in the line with subsequent disruption or change of air flows. The
tube may be insulated by covering it with plastic tubing having an inside
diameter slightly larger than the outside diameter of the exhaust tube.
2.2.3 Spatial Requirements
Adequate space should be allotted for analyzer operation and calibra-
tion. If the instrument (or instrument modules) is rack-mounted, there
should be sufficient space around the rack to allow free circulation of air
to provide good heat dissipation. The bench mount configuration is quite
handy as it allows convenient access to the interior of the analyzer for
maintenance and adjustment.
In either case, sufficient room should be available adjacent to the
analyzer to locate a sulfur calibration source and associated equipment such
as bubble flowmeters and mass flowmeters. It is a good idea, if space
permits, to have easy access to the rear panel of the analyzer so that
electrical and pneumatic lines and in-line filters and scrubbers can be
easily checked or changed.
2.2.4 Ambient Air Sampling Requirements
Air should be brought into the sampling station through an ambient air
sampling manifold of glass or Teflon construction. A 60-100 cfm (free air)
blower motor is located at one end to pull the air sample into the station
at the rate of several cubic feet per minute and exhaust the excess air to
the outside. The blower motor should be easily accessible for periodic
checks of its proper operation. The glassware of the manifold itself should
be disassembled and cleaned from time to time, especially when dust and dirt
buildup becomes noticeable. Clean it with warm water and rinse with deion-
ized water. The Teflon sampling line of the analyzer is connected to the
manifold. Figure 2.1 illustrates several ways to make this connection.
Whatever way is used, it should be compatible with both the ambient air and
calibration manifolds. Air inlets of calibration systems which "manufac-
ture" zero air for use with permeation tubes or other calibration gas
sources are also connected to the sampling manifold. In this way, ambient
20
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SAMPLING OR CALIBRATION MANIFOLD
BALL/SOCKET JOINT ^
HELD BY SPRING- "
LOADED CLAMP
1/4 IN. OD
GLASSTUBE-
1/4 IN. TO 1/8 IN.
TEFLON REDUCING
UNION
1/8 IN. OD TEFLON
SAMPLING LINE TO
INSTRUMENT
•SAMPLING TUBE EXTENDS THROUGH THE
GLASS CONNECTOR INTO THE MANIFOLD
V
1/4 IN. OD GLASS TUBING, DRAWN DOWN
AT ONE END SO THAT A 1/8 IN. OD TUBE
JUST PASSES THROUGH
LARGER TYGON TUBING (OR EQUIVALENT)
(SMALLER TYGON TUBING (OR EQUIVALENT)
• 1/8" OD TEFLON SAMPLING LINE
SAMPLING OR CALIBRATION MANIFOLD
PLASTIC CAP,
*
TEFLON-COATED
COMPRESSION
GASKET
HREADED GLASS FITTING'
1/4 IN. OD TEFLON
OR GLASS TUBE
1/4 IN. TO 1/8 IN.
TEFLON UNION
1/8 IN. OD TEFLON
SAMPLING LINE TO
INSTRUMENT
1/4 IN. OD GLASS TUBING, DRAWN DOWN
• AT ONE END SO THAT A 1/8 IN. OD TUBE
JUST PASSES THROUGH
- LARGER TYGON TUBING
SMALLER TYGON TUBING
Figure 2.1. Detailed views of various ways for connecting 1/8 in. o.d.
Teflon sampling lines to manifold.
21
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levels of carbon dioxide (C02) are supplied to the instrument. Refer to
Section 3.0 for a discussion of the C02 effect on FPD analyzers.
Do not sample ambient air by running lengths of Teflon tubing from the
instrument to the exterior of the station. Such long lines give problems
with pressure balance and moisture condensation and collect dust. They also
are awkward to use during calibration and zero and span checks.
Detailed instructions for installation of sampling manifolds are given
in EPA document EPA-600/4-77-027a, "Quality Assurance Handbook for Air
Pollution Measurement Systems-Volume II, Ambient Air Specific Methods."
2.3 INSTALLATION OF AN FPD S02 ANALYZER
2.3.1 Unpacking the Analyzer
Upon receipt, the analyzer should be unpackaged and examined for damage
such as scratched surfaces, broken or bent control knobs, etc. Check the
contents of the package against the packing slip which accompanies the
parcel. If there are shipping deficiencies, report them to the manufac-
turer; if there is damage from shipping, report this to the freight carrier
and file a claim.
Prior to applying any power to the analyzer, it is a good idea to
remove the cover of the analyzer and visually inspect the interior. All
analyzers contain electronic "cards" or "boards" which plug into special
sockets; there is a chance one may be loose or not in place. Refer to the
manufacturer's operation and service manual for directions for handling and
replacing electronic boards.
Some instruments may also have the sampling pump "tied-down" for ship-
ping purposes. Remove any such tie-down straps. Again, if there is any
doubt concerning the location of components of an analyzer, refer to the
manufacturer's manual.
Save the shipping box or crate in the event the analyzer may have to be
returned to the manufacturer or be moved to another site.
2.3.2 Electrical and Pneumatic Connections
Electrical and pneumatic (gas) connecting terminals are located on the
rear panel of most FPD S02 analyzers. Figure 2.2 illustrates a typical
installation.
22
-------
PO
CO
RECORDER
SIGNAL
CABLE
PRIMARY--,
POWER ^
VENT
DIGITAL
VOLTMETER
(OPTIONAL)
1/8IN. ODSTAINL
_ STEEL TUBING
ANALYZER INLET
RECORDER AND/OR
DATA SYSTEM SIGNAL _^
OUTLET SAMPLE HJ h £
INLET 1 F
H2S SCRUBBER
1 PI IMP 1 "C3 INLET FOR
PUMP | ^DILUTION AIR
1 r^-1 PARTICULATE
v. IM nn DI-II VCTHVI PMP FILTER
TWO STAGE
REGULATOR \
HYDROGEN
CYLINDER OR
GENERATOR
ESS
_ 1/8 IN. OD TEFLON
1 « *\AMPI
TEFLON
FILTER
TUBING
DILUTION
AIR IN
Figure 2.2. Typical installation of FPD S02 analyzer.
-------
2.3.2.1 Electrical Connections
On the rear of each kind of FPD S02 analyzer will be a terminal strip
for electrical output connections to a recorder and/or data acquisition
system (DAS). Connections to the screws on this terminal strip are best
made with no. 6 spade lugs (available from electrical supply houses) which
have been carefully connected to the signal cable. The cable interconnect-
ing the analyzer to the recorder or DAS should be shielded twin lead wire
(commonly called control, instrumentation, or signal cable) and should be of
minimal length, less than 15 m (50 ft). The shield portion of the cable
should be connected to the signal low at the analyzer and left unconnected
at the recorder or DAS end. If the recorder or DAS is equipped with a
guarded input, refer to its manual for proper interconnection instructions.
Special connectors or plugs may be required for connection to the
recording device. Avoid any sort of wire splicing that involves twisting
wires together and wrapping with tape. A continuous length of wire is
preferred. If splicing is necessary, a good quality soldering job should be
done and the wire reinsulated. The use of the mechanical compression con-
nectors, such as "sta-kons," is acceptable.
2.3.2.2 Pneumatic (Gas) Connections
Any of the commercial FPD S02 analyzers will require connection of at
least three gas lines to the rear panel of the analyzer. These are the
ambient air sample line, the hydrogen fuel line, and the exhaust gas line.
Be sure to follow the manufacturer's directions for use of tube connectors
and compression fittings so that a leak-free assembly is obtained.
Ambient air sample line and filter. All manufacturers specify the use
of 3.2 mm (1/8 in.) o.d. x 0.76 mm (0.030 in.) thick wall Teflon tubing. A
roll of this should be available. Be sure this tubing is clean and has not
been used previously. Do not use copper, steel, polyethylene or other
plastics for sample tubing! Tubing of uncertain cleanliness may be cleaned
by passing reagent grade methanol (methyl alcohol, a poison) through it and
then drying the tube interior with clean, dry nitrogen or air. Certain tube
connecting fitting (Swagelok , Parker-Hannifin®, Gyrolok®, etc.) may be
needed. Use only Teflon fittings or all-glass connecting devices.
24
-------
The length of the sampling tube should not be excessive. Usually a
length of 1.5 m (4 to 6 ft) is ample to reach the station sampling manifold.
Use this line for both sampling and calibration.
It is recommended that an all-Teflon particulate filter be installed in
the instrument sampling line. The filter should be a Teflon membrane with 5 u
or less pore size. Its holder should be constructed from a solid piece of
Teflon or metal which is completely lined with Teflon. A suggested model is
the Mace filter holder, series 930 (available from the Mace Corporation,
S. El Monte, CA 91733) used in conjunction with 5 u Teflon membrane filters,
catalog no. 425-0001 (see Figure 4.1). Use of non-Teflon filters can de-
stroy the S02 sample and may cause pressure problems in the analyzer's
pneumatic system. Consult the manufacturer for his specific recommenda-
tions. The membrane filter should be replaced at the time of calibration,
or more often if the instrument is located in a particularly dirty environ-
ment.
Exhaust gas line. The instrument's exhaust line should be 6.3 mm (1/4
in.) or greater o.d. polyethylene tubing. Since moisture may accumulate in
this line, be sure it is installed in such a way that drainage will always
occur. In some older FPD models, the exhaust line is connected to an exter-
nal pump which has its own exhaust line. Any exhaust lines should be of the
minimum length required to exhaust gases from the station.
Hydrogen fuel line. It is recommended for safety reasons that connec-
tion of the hydrogen supply (from a compressed gas cylinder or an electro-
lytic hydrogen generator) to the analyzer be made only through clean, dry
stainless steel tubing. The tubing should be 3.2 mm (1/8 in.) o.d. Use
stainless steel fittings. The hydrogen, if supplied from a cylinder, should
be of "prepurified" grade or an equivalent or better grade. Percent purity
is 99.95 or better.
The regulator used with the compressed hydrogen cylinder should be a
two-stage metal diaphragm brass regulator with a delivery pressure range
between 0 and 150 psig and should be equipped with CGA no. 350 cylinder
valve outlet. This regulator must be free of sulfur-containing materials in
its construction. Brass, stainless steel, and Kel-F or Teflon are suitable
materials for internal construction. This regulator should be dedicated to
use with H2. A shut-off valve should also be included. A very important
25
-------
safety consideration would be the installation of a flow-limiting orifice
near the regulator to limit the flow in case a leak or rupture occurs. A
hydrogen regulator assembly is shown in Figure 2.3.
Observe the following safety requirements in the handling and use of
hydrogen since it is an explosive material.
2.3.3 Guidelines for the Safe Use of Hydrogen Cylinders
Hydrogen is a highly flammable gas which is colorless, odorless, and
tasteless. It burns in air with a flame that is almost invisible. Its
chemical formula is H2, its molecular weight is 2.016, and it is flammable
in the 4 to 75% (by volume) range in air. A temperature of 585° C (1,085° F)
is required for auto-ignition in mixtures of air or oxygen at atmospheric
pressure. A spark can of course cause ignition at ambient temperatures.
Electrical relays, contact closures, etc. are causes of sparks.
Precautions for handling and storing of hydrogen cylinders
The major hazard associated with the handling of hydrogen is its flam-
mability. Be certain to follow these rules when handling hydrogen cylin-
ders:
1. Never use cylinders of hydrogen in areas where flames, excessive
heat, or sparks may occur.
2. Utilize only explosion-proof equipment, and spark-proof tools in
areas where hydrogen is handled.
3. Ground all equipment and lines used with hydrogen.
4. Never use a flame to detect hydrogen leaks—use water or a
aj>fc
commercial liquid leak detector such as "SNOOP ."
5. Do not store reserve stocks of hydrogen with cylinders containing
oxygen or other highly oxidizing or combustible materials.
Precautions for H9 cylinder use with FPD analyzers
1. Never move a hydrogen cylinder unless the regulator is removed
and the cylinder cap is in position. Use a cylinder cart and
chain the tank to it. Gloves and safety glasses or full face
shield should be worn when moving tanks.
2. Do not expose the H2 tank to mechanical stress by dropping it
to the ground or dropping it from truck tailgates.
26
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SHUTOFF
VALVE
NOTE THE INDENTIONS IN THESE FITTINGS -
INDICATES "LEFT-HANDED" THREADS
COMPRESSION
FITTINGS
FLOW LIMITING
ORIFICE
CYLINDER VALVE
SAFETY NUT
(DO NOT REMOVE)
CLEAN 1/8" O.D.
STAINLESS STEEL
TUBING
TWO STAGE METAL
DIAPHRAGM
REGULATOR
CYLINDER
OUTLET CAP
CYLINDER VALVE
OUTLET CGA #350
•^—
\
HYDROGEN
CYLINDER
Figure 2.3. Hydrogen regulator assembly and CGA cylinder connecter #350.
-------
3. Locate the hydrogen cylinder in a well-ventilated area. If this
is inside a building, be sure the tank is separated from nearby
oxygen- or air-containing tanks. The H2 tank may also be located
outside the building. If outside, keep the tank protected from
the weather, from sources of heat, flame, or sparks, and separate
from oxygen or air cylinders.
4. Properly secure the hydrogen cylinder to a permanent or semi-
permanent structure (such as a railing attached to the wall studs
or to a laboratory benchtop) using a cylinder clamp with strap or
chain. Be certain to have the cylinder properly secured before
removing the cylinder cap and attaching a regulator.
5. The hydrogen cylinder and all equipment and lines associated with
it should be electrically grounded. The three-wire grounding
system of the analyzer grounds the analyzer and connections.
6. Never open the tank output valve or the regulator valve before
connection is made to the analyzer. Self-ignition (auto-ignition)
of the escaping hydrogen may occur. When the cylinder valve ^s
open, open it all the way (counterclockwise) until turning stops.
Leakage may occur at intermediate positions.
7. Connect the H2 cylinder to the fuel entry port at the rear of the
analyzer using only 3.2 mm (1/8 in.) o.d. stainless steel lines.
Leak test the lines only with water or commercial leak check solu-
tions such as "SNOOP ." To pressurize the line for a leak test:
(a) verify that all connections are made and are tight from the
cylinder outlet to the rear of the analyzer (test by snugging the
fittings with wrenches); (b) be certain the analyzer is off so
that the H2-shut-off solenoid is closed, be certain the hydrogen
regulator is closed (i.e., the pressure-adjusting knob or handle
is rotated counterclockwise until it moves freely); (c) quickly
open or "crack" the cylinder regulator's main valve, watch the
pressure rise in the gauge nearer the tank (the pressure in a new
H2 tank at 21° C (70° F) is about 2,200 psig), and then immedi-
ately close the cylinder valve. If the gauge pressure decays as
you watch, there is a leak in the regulator's connection to the
cylinder or a leak through the regulator. If no leaks are indi-
28
-------
cated, the pressure on the second gauge should be set to some
point (say, 40 psig or the FPD analyzer's suggested setting).
This will pressurize the line up to the instrument H2 shutoff
solenoid. Any major leaks will be indicated by a rapid decay of
pressure in the regulator gauge. Check for small leaks by apply-
ing leak-detector solution around each connection and watching for
small bubbles to form as the hydrogen escapes.
8. Never loosen or disconnect any hydrogen fitting or connector while
the hydrogen is under pressure. Always cut the hydrogen off at
the tank and allow the system to "bleed" down to ambient pressure.
9. In the event a major leak occurs while the hydrogen is under pres-
sure, turn off the cylinder valve if possible and leave the sta-
tion. Leave the door open for ventilation. Cut off electrical
power at the breaker box outside the station.
10. When connecting the regulator to the cylinder, do not confuse the
cylinder safety nut with the metal outlet cap which is frequently
installed on the cylinder outlet. The safety nut connects di-
rectly to the valve inlet and once it is removed, the flow of gas
cannot be stopped. Refer to Figure 2.3.
2.3.4 Procedures and Safety Precautions for Use of Electrolytic
Hydrogen Generators
Electrochemical hydrogen generators produce hydrogen (H2) (and oxygen
(02)), by electrolysis of water. As with any hydrogen supply, one must be
cautious in the use of the generator. Become thoroughly familiar with the
manufacturer's operation and maintenance manual before using your hydrogen
generator. Practice preventive maintenance.
It is recommended that the hydrogen generator be dedicated to use with
the flame photometric detector and not shared with other analyzers. If two
or more analyzers do share the same hydrogen generator, be sure that ade-
quate pressure regulation and flow control is maintained to each analyzer.
All hydrogen generators, of course, produce oxygen concurrently. In
some generators the oxygen is vented and not used. In others, the oxygen is
dried and stored (under pressure) for laboratory use. The most trouble-free
29
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operation for FPD analyzers has been found with generators intended for
hydrogen production only.
Certain precautions must be observed for successful, long-term, and
safe use of hydrogen generators. Important points are:
1. Do not defeat the grounding three-wire power cord.
2. Fill the solution reservoir of the generator only with
the manufacturer's specified solution.
4.
5.
Exercise caution not to overfill the reservoir. If
it is overfilled, water may be forced through the
hydrogen line to the instrument. Follow the manufac-
turer's instructions.
Some generators use only deionized distilled water. If
water containing metallic impurities is used, the electro-
chemical cell will be damaged or contaminated. Deionization
of the water may be required in the generator reservoir.
Keep deionization bags or cartridges fresh.
Other generators use caustic solutions of sodium hydroxide,
or acidic solutions. Exercise care in handling these
solutions.
Do not operate a hydrogen generator in a sealed or unvented room.
Do not use near open flames or other sources of ignition.
Never allow the 02 vent line to be obstructed.
Check the water or electrolytic solution level often. If the
level gets low, the generator will cut off.
When first turning on the generator, allow it to develop a normal
internal pressure before connecting to analyzers.
Change the desiccant cartridge often to maintain dry hydrogen gas.
Be careful to reseal the desiccant cartridge carefully so it is
leak-tight. Do not apply pressure to plastic parts with wrenches
or other tools. To do so may cause cracking or stress lines and
H2 leakage could result.
Minimize the volume of hydrogen stored in lines and desiccant
cartridges by minimizing the size of the line and the hydrogen
pressure.
30
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2.4 STARTUP OF AN FPD S02 ANALYZER
2.4.1 Power On; Warmup Times
With newer models of FPD S02 analyzers, only the main power switch (and
perhaps an electronics switch) needs to be turned on. The air and fuel
ignite automatically in a preprogrammed sequence. Since hydrogen gas does
not flow to the analyzer until the power is turned on (the safety solenoid
is closed in the power off mode), it may take several attempts before the
flame lights. Most analyzers have a front panel lamp which indicates when
the flame is lighted.
With older model analyzers, it is necessary to ignite the flame man-
ually by depressing a switch which activates a "glow-plug" in the burner
chamber. At times, it may be difficult to ignite the flame. One procedure
to follow is this: engage the flame-out override feature; turn the hydrogen
flow rate almost off by adjusting the hydrogen needle valve or rotameter on
the instrument's front panel; depress the ignite switch; slowly increase the
hydrogen flow while you continue to activate the ignite switch; when a "pop"
is heard, or the ball of the hydrogen rotameter "bounces," release the
ignite switch. Complete this operation in 5 seconds or less. Do not at-
tempt to start ignition when any flow of hydrogen is present. Rapid igni-
tion may damage the combustion chamber. If the flame is burning, the indi-
cator lamp will be unlighted and the hydrogen rotameter will continue to
indicate flow. Reset the rotameter ball to the desired or preset position.
A significant change in hydrogen flow can alter the calibration.
Some older models of Meloy analyzers have the following feature which
should be noted: a flame-out occurs (i.e., the H2 solenoid closed) when the
analyzer response voltage became negative. New models have a temperature
sensor to detect an actual flame-out and cause the H2 solenoid to close.
Other early models lacked the hydrogen shut-off solenoid feature. If the
flame went out, H2 continued to flow. For such analyzers, be sure to vent
the exhaust to the outside of the station.
A certain length of time will be required for the hydrogen to purge the
air which may be present in the lines and give a mixture suitable for igni-
tion at the burner tip. Other flame-out problems may be due to irregular or
mismatched H2/air sample flows, water condensation in the burner compart-
31
-------
ment, or a damaged or corroded burner tip, or mis-adjusted cams on instru-
ments equipped with timers. Refer to the manufacturer's instruction manual
for servicing and cleaning of burner compartments.
Warmup times may vary from instrument to instrument. It is a good idea
to allow 24 hours before beginning calibration. A stable zero air or span
gas trace on a strip chart recorder is a useful indicator of instrument
stability.
Some analyzers have a flowmeter (rotameter) which indicates the flow of
sample air through the instrument. Use this only for establishing or veri-
fying a flow rate. Bypass this rotameter (by deactivating a solenoid valve)
during the time of calibration or ambient air sampling.
2.4.2 "Peaking Up" Response Prior to Calibration
After the flame has burned for a few minutes, the air flow and the
hydrogen flow should be adjusted to the manufacturer's recommended settings.
The hydrogen flow is generally set by use of a rotameter. The sample air
flow may also be set with a rotameter. This sample air rotameter should be
bypassed in normal operation. A soap film flowmeter or mass flowmeter may
also be used to determine and set the sample flow rate. Flow rates are
generally around 150-200 cmVmin.
Certain early models of Bendix analyzers have a burner tip whose height
can be altered. The tip is threaded and can be moved up and down. This
height is set at the factory. However, if the burner block is disassembled
and cleaned, it may be necessary to test the analyzer with the burner tip at
several different heights to optimize the signal. Consult your Bendix
service representative for advice on the most efficient way to optimize the
signal.
After the analyzer has warmed up, the operator proceeds to the calibra-
tion of the analyzer, described in Section 4.0 of this document. Calibra-
tion devices to generate known S02 concentrations are described in Section
3.0.
With new analyzers, the manufacturer supplies a "checkout sheet," which
gives the results of the manufacturer's calibration and electrical constants
for the particular analyzer. This sheet should be consulted during the
initial calibration procedure. If your results do not agree fairly closely
32
-------
with the checkout sheet, the instrument may be damaged or improperly in-
stalled or your calibration and measurement system may be in error.
33
-------
34
-------
SECTION 3.0
GENERATION OF S02 CALIBRATION STANDARDS AND ZERO AIR
3.1 INTRODUCTION
The accuracy and validity of data derived from any air monitoring
instrument is dependent upon the type and extent of quality control prac-
tices and procedures. Instrument calibration is the first element of data
quality control and is the key to comparison and utilization of data pro-
duced by federal, state, local, and private air sampling networks.
Any monitoring instrument, such as the continuous FPD S02 analyzer, is
subject to drift and variation in internal parameters and will need periodic
calibration.
The recommended method of calibration is a direct, dynamic calibration
utilizing the same pollutant species in the same air diluent as is being
monitored. In the dynamic method, a known amount of pure or concentrated
gaseous pollutant is mixed with diluting air as the mixture is used. A
dynamic calibration of ambient air analyzers should generally be a multiple
point calibration. That a multipoint calibration be performed is especially
important in the case of the FPD, since its response is approximately propor-
tional to the second power of S02 concentration and the more points, the
better the calibration curve can be established. This calibration should be
performed at the site of the analyzer (i.e., "in the field"). Reliable,
portable equipment makes this possible. Many FPD analyzers now have linear-
ized responses. Multipoint calibration is still important since in this way
the operator will know that the linearization circuitry is properly ad-
justed. Another way to determine linearity is by simulating S02 response
with a picoamp source. Consult the manufacturer's literature for details.
This section of the technical assistance document will discuss cali-
brator systems which may be used for generation of S02 gas standards for
35
-------
calibration of FPD as well as other types of S02 analyzers. The reproduci-
bility, reliability, and accuracy of any system depends heavily on four
aspects: reliable, known, certified sources of S02 (preferably NBS certi-
fied or NBS traceable); stable and accurately known temperatures of S02
permeating devices; known flow rates of dilution air; a proper source of zero
or diluent air.
3.2 CLEAN AIR SOURCES FOR S02 CALIBRATION SYSTEMS
A source of clean, dry, sulfur-free air is necessary for various uses
in all dynamic calibration systems. With FPD S02 analyzers, it is obvious
that air, rather than nitrogen or some other inert gas, must be used since
otherwise the detector flame would be extinguished. The nomenclature de-
scribing diluent air varies. Zero air is the name used when the clean air
is sampled by the analyzer to allow the setting of the zero concentration
signal output. Diluent air is the name given to air used to dilute a stream
of air containing relatively high concentrations of S02. Sweep air or purge
air is the term used when clean air sweeps or purges the effluent from a
permeation tube or device.
This air must have certain characteristics in order to be employed in
calibration of FPD S02 analyzers. Its water vapor content must be at levels
where condensation does not occur; it must possess the ambient percentage
(20.94) of oxygen found in air (since the flame of an FPD is sensitive to
the oxygen/nitrogen ratio); it must retain ambient concentration levels of
carbon dioxide, C02, (since the FPD has some degree of sensitivity to C02);
and of course it must be free of all sulfur-containing compounds.
Since the same source of air is often used to prepare zero and cali-
bration gas for other pollutant monitors, removal of other pollutants is
another desirable feature.
3.2.1 Zero Air Generators
Figure 3.1 shows the basic components and general specifications of a
zero air generator which will produce air suitable for use in calibration of
FPD S02 analyzers.14 Greater details on this system are given in the refer-
ence. Such a system is suitable for 99 percent removal of nitric oxide, NO,
N02) S02, H2S, and other pollutant gases. It allows C02 in ambient air to
pass through unaffected.
36
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OUTDOOR AMBIENT
AIR IN
(1) INERT SURFACES,
METAL OR
TEFLON.
PUMP SUCH
AS METAL
BELLOWS OR
DIAPHRAGM
PUMP
(DUV LAMP
(2) [03] a 0.3
ppm AT 16
6pm IN AIR
(3) INERT INTERNAL
SURFACES
(4) LOW PRESSURE
DROP, <10cm
H20
(1) ACTIVATED CHARCOAL;
6-12 MESH ACTIVATED
COCONUT SHELL
CHARCOAL
(2)TURBULENT FLOW
(3) LENGTH TO DIAMETER
RATIO >5
(4) LOW PRESSURE DROP,
<10 cm H20
(5) LONG SCRUBBING
CAPACITY LIFETIME-
40 HOURS OR
LONGER WITH
CONTINUOUS
OPERATION
co
000
HPARTICULATELJ |_| DRYING LJ OX|D|ZER
FILTER
o
(1) LOW PRESSURE DROP,
<10 cm H20.
FILTER SUCH AS
15 MICRON BRASS
OR TEFLON
MATERIAL
"""" COLUMN 1 1
o
(1) INDICATING
SILICA GEL,
ACTIVATED,
3-8 MESH
(2) TURBULENT FLOW
(3) LENGTH TO
DIAMETER RATIO
>5
(4) LOW PRESSURE
DROP, <1 Ocm
H20
u — u
O
(1) INERT INTERNAL
SURFACES.
(2) LONG AIR RESI-
DENCE TIME
@16 £pm
(3)>98% REACTION
COMPLETION
(4) LOW PRESSURE
DROP, <10 cm
H20
S02 SCRUBBER
(ONE OR MORE)!
ZERO A
TO FLO!
CONTRC
ROT AMI
AND PEI
TION DE
COMPAR
Figure 3.1. Zero air generator suitable for FPD S02 zero and calibration.
-------
The oxidizer and reactor components are not required for zero gas
production for S02 analyzers; they are present to remove NO by reaction with
ozone and conversion to N02 which is removed by the charcoal. Thus the
system may be used as a zero air source for calibration of NO monitors.
/\
There are many types of clean air supplies in use which process ambient
air. Unfortunately, not all of them can be used to supply zero or diluent
air to any type of ambient air analyzer. The definition of zero air has a
meaning not only in terms of the pollutant response of the analyzer, but
also in terms of the analyzer's interferent molecular responses. For the
case of the FPD S02 analyzer, zero air must not contain sulfur compounds but
must contain ambient C02 levels. For instance, it has been found that
heatless air dryer clean air systems are not suitable as calibration air
sources for the FPD analyzer. This is because the heatless air dryer system
selectively retains C02 on the molecular sieve dryer column, and the back-
flush cycle prevents C02 from passing through the system.
If the air supply requires drying, a Drierite (TM) or silica gel scrub-
ber is suggested. These materials have been shown to pass C02 without
diminishment. The Perma-Pure (TM) dryer is also an acceptable alternative.
Any air supply which contains Ascarite, soda lime or other air scrub-
bers known to remove C02 cannot be used. Regenerative molecular sieve
dryers cannot be used. Activated alumina dryers or scrubbers should also
not be used since alumina is partially selective in absorption of C02.
If the C02 content of the air produced by the clean air system(s) in
your laboratory is unknown, it should be determined and compared to ambient
air concentrations determined simultaneously.
Ambient air for the clean air system should be obtained
from outside the station (the station's sampling manifold
is a convenient source) not from within the station or
laboratory since room air will have elevated concentra-
tions of C02. The C02 content of the air produced by the
clean air supply should be determined and compared to the
C02 content of ambient air.
A gravimetric procedure for determination of C02 concentration in air
(by absorption of C02 on Ascarite) is given in Section 5.0 of this document.
Determinations done simultaneously on air from the calibration system and
38
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from ambient air should match fairly well. If the C02 content from the
calibration system is much lower than that of ambient air, the system should
be improved.
3.2.2 Compressed Air Cylinders
Compressed air cylinders or other compressed air supplies are also used
to supply air for calibration purposes. It is important that this air have
the following properties for use with FPD analyzers:
a. The same 02 and N2 percentage composition as ambient air (20.94%
02, 78.08% N2).
b. A C02 content similar to that of ambient air, somewhere between
300 and 350 ppm. If the average C02 at a particular monitoring
site is significantly greater than 350 ppm, then the cylinder
should contain the higher level. One way to specify this when
ordering would be to order a specialty gas mixture of C02 (350
ppm) in zero air.
If this air contains sulfur compounds and/or particulate matter, it must be
cleaned by passage through an activated charcoal scrubber system and/or a
particulate filter.
For calibration systems based on dilution of high level cylinder con-
centrations of S02 in air or nitrogen, the presence of ambient concentra-
tions of C02 within the S02 standard cylinder is not necessary if the sam-
ple: air dilution ratio is small (such as 1:500) and the diluent air is zero
air containing ambient concentrations of C02.
On the other hand, if low-level S02 in air cylinders are used for
calibration or audit checks, the cylinder should contain ambient levels of
C02 since the contents of the cylinder will be routed directly to the cali-
bration manifold with little or no dilution.
3.3 PERMEATION TUBES AND DEVICES CONTAINING LIQUEFIED S02:
CHARACTERISTICS AND USE
3.3.1 Introduction
A liquifiable gas, when enclosed in an inert plastic tube (i.e.,
Teflon), escapes by permeating the wall at a constant, reproducible,
temperature-dependent rate. The rate of escape of gaseous S02 from a
39
-------
permeation tube is determined gravimetrically. The weight loss of the tube
is equated to the weight of the escaping material. Further background
information concerning the theory, construction, and behavior of permeation
tubes or devices can be found in the literature.15'16'17'18'19
Today, most S02 permeation tubes are purchased directly from suppliers
with the rate of permeation (stated in micrograms/minute or nanograms/minute)
pre-established. For ambient air calibration work, a reliable source of
permeation tubes in the United States is the National Bureau of Standards
(NBS). The NBS permeation tube is in fact a Standard Reference Material,
SRM. If another supplier is employed, be sure to request a calibration
certificate which states that the tube's permeation rate is traceable to NBS
Standard Reference Material.
Some calibrators may use only special permeation devices. These are
not tubes but are wafers or cylinders. Such devices should also be pur-
chased with certificates of traceability to NBS standards or be compared in
the laboratory to an NBS Standard Reference Material.
3.3.2 Description of NBS Permeation Tubes
The National Bureau of Standards supplies three different size S02
permeation tubes. A diagram of a tube is shown in Figure 3.2. Each tube is
calibrated individually and is certified as a Standard Reference Material
(SRM). They are:
SRM No. Size Nominal Permeation Rate at 25° C
1627 2 cm 0.56 micrograms/minute
1626 5 cm 1.4 micrograms/minute
1625 10 cm 2.8 micrograms/minute
Figure 3.3 is a copy of the NBS Certificate for SRM No. 1626. It lists
the method of calibration of the tube and gives use and storage information.
Table 3.1 is a copy of a table which shows the relationship between
temperature and permeation rate for an actual NBS permeation tube. The
table also gives an equation of the form log R = mt + b which can be used to
compute permeation rates at other temperatures within the range of certifi-
cation. Caution! This equation applies only to tube number 33-64.
40
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TEFLON TUBE
\
'5mm
TEFLON PLUG
RETAINING COLLAR INDICATING
TUBE I.D. NUMBER "33-64"
LIQUEFIED SO2 GAS
RETAINING COLLAR
INDICATING TUBE
CONTENTS, "SO2"
Figure 3.2. National Bureau of Standards standard reference material
S02 permeation tube.
-------
National Bureau of Standards
Certificate
Standard Reference Material 1626
Sulfur Dioxide Permeation Tube
(Individually Calibrated)
E. E. Hughes and W. P. Schmidt
This Standard Reference Material consists of a 5 cm sulfur dioxide permeation tube, individually calibrated, for use in the
preparation of gases of known sulfur dioxide content. It is intended for standardization of apparatus and procedures used in air
pollution and related chemical analyses. Permeation rates for temperatures in the range of 20 to 30° C are given in the table ac-
companying each tube.
The tabulated values result from determinations of the permeation rates for the specified tube, using the method described on
the reverse of this certificate. The uncertainty of the certified permeation rates, based on the results of the calibration of approx-
imately 25 tubes, is less than ± 0.5 percent at 25° C and does not exceed ± 1.0 percent at 20 and 30° C. respectively.
Experiments in this laborabory have shown that the calibration remains valid as long as visible amounts of liquid sulfur diox-
ide remain in the tube.
The calibration measurements were made by E. E. Hughes and W. P. Schmidt, Analytical Chemistry Division, NBS Institute
for Materials Research.
The overall direction and coordination of the technical measurements leading for certification were performed under the chair-
manship of J. K. Taylor.
The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference Material
were coordinated through the Office of Standard Reference Materials by T. W. Mears.
Washington, D. C. 20234 j. Pau| Cali( chief
August 12, 1971 Office of Standard Reference Materials
Figure 3.3. National Bureau of Standards sulfur dioxide
permeation tube certificate
42
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CALIBRATION
This tube was individually calibrated by gravimetric determination of weight losses at 20, 25, and 30° C, respectively. The
tube was held at constant temperature for several days at each level, and the permeation rate was determined by weighing the
tubes at 24-hour intervals, using a micro-balance. The measured rates were fitted by the method of least squares to an equation of
the type log R = mt + b. The resulting equation, given on the table accompanying the tube, was used to calculate the values of
the permeation rates.
The precision of calibration was estimated from measurements on approximately 25 tubes in this lot at each calibration
temperature. The uncertainties indicated are the approximate half width of the 95 percent confidence interval. It is believed that
the systematic errors concerned with the calibration are negligible.
USE
This tube can be used to produce known concentrations of sulfur dioxide in a gas stream when both the temperature and flow
rate of the gas stream are known. Apparatus and techniques for this purpose are described in references [3] and [4] and should be
consulted for operational details. Because of the large temperature coefficient of the permeation rate, approximately 9 percent
per degree Celsius, the temperature must be maintained constant and measured accurately to 0.1° C to provide concentrations
consistent with the calibration uncertainty.
It is recommended that the tube temperature be held constant during use and that desired concentration levels be achieved by
adjustment of the flow rate. If it is necessary to vary the concentration by changing the tube temperature, a suitable time interval
must be allowed for equilibrium of the permeation rate to be re-established. For changes of 1 or 2 degrees Celsius, a period of 3
hours should suffice. For changes of 10 degrees or when removed from low temperature storage, a period of 24 hours is advisable.
This permeation tube is a stable and relatively rugged source of sulfur dioxide and no extreme measures are necessary to en-
sure that the calibration of the tube will be maintained during its useful life. However, it should be treated with the care
necessary to assure the user that no change occurs in the character of the tube. Precautions should be exercised to prevent con-
tamination of the outer surface during handling. The tube should be protected from high concentrations of water vapor during
storage and use. A relative humidity of 10 percent should have no effect on the permeation rate within the calibration uncertain-
ty.
STORAGE
The useful life of this certified sulfur dioxide permeation tube is about 9 months. Storage at lower temperatures will prolong
the life. However, it should be protected from moisture during storage. On removal from low temperature storage, the tube
should be equilibrated at the operating temperature for at least 24 hours, before use as an analytical standard.
PRECAUTION
This permeation tube contains liquid sulfur dioxide at a pressure of about 4 atmospheres at room temperature. While no
failures have occured during use, there is the possibility of rupture due to internal pressure. However, it is believed that normal
handling of the tubes at temperatures up to and slightly exceeding 35° C does not constitute a hazard.
SELECTED REFERENCES
[]] A. E. O'Keeffe and G. C. Ortman, Anal. Chem. 38, 760 (1966).
[2] F. P. Scaringelli, S. A. Frey, and B. E. Saltzman, Amer. Ind. Hyg. Assoc. J. 28, 260 (1967).
[3] Health Laboratory Science 7, No. 1, 4 (1970).
[4] F. P. Scaringelli, A. E. O'Keeffe, E. Rosenberg, and J. P. Bell, Anal. Chem. 42, 871 (1970).
[5] J. K. Taylor, Ed., NBS Technical Note 545, December 1970.
Figure 3.3. National Bureau of Standards sulfur dioxide
permeation tube certificate (con.)
43
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Table 3.1. Certified permeation rates for National Bureau of
Standards permeation tube No. 33-64.
CERTIFIED PERMEATION RATES FOR TUBE NO. 33- 64
TEMPERATURE C PERMEATION RATE, SO2
MICROGRAM/MIN
20.00 .832
21.00 .899
22.00 .972
23.00 1.050
CAUTION! 24.00 1.135 CAUTION!
EXAMPLE 25.00 1.227 EXAMPLE
ONLY! 26.00 1.326 ONLY!
27.00 1.433
28.00 1.549
29.00 1.674
30.00 1.810
THE PERMEATION RATE IS REPRESENTED BY THE EQUATION
LOG R = M(273.15+T)-B
WHERE M = .033759, B = 9.97634 AND T IS TEMPERATURE IN DEGREES C
THIS EQUATION MAY BE USED TO CALCULATE RATES AT INTERMEDIATE
TEMPERATURES, NOT TABULATED, AND TO ESTIMATE VALUES AT
TEMPERATURES NOT MORE THAN 2 DEGREES C. BEYOND THE RANGE OF THE
TABLE. HOWEVER, THE TUBE IS NOT CERTIFIED FOR TEMPERATURES
OUTSIDE THE RANGE GIVEN IN THE TABLE.
-------
3.4 CALIBRATION SYSTEMS BASED ON PERMEATION DEVICES: DESCRIPTION
AND EXPLANATION OF USE
3.4.1 Custom-built Laboratory Systems Employing Permeation Tubes
Many S02 calibration gas sources have been custom-built for laboratory
use. Such systems generally employ water baths for temperature control and
glass condensers as permeation tube holders. Such systems are inconvenient
for use in the field because of their bulk and fragility. A system suitable
for generation of S02 atmospheres (and with minor modification, H2S and N02)
is shown in Figure 3.4. A schematic of a laboratory clean air supply is
shown in Figure 3.5. The numbered components of the system are discussed
below.
The system shown in Figure 3.5 is built around a "Forma Temp Jr."
constant temperature water circulating bath (1), which has an approximate 8
liter (2 gallon) capacity, controls water temperature to ±0.1°C, by alternate
heating and cooling, has a variable temperature range of 15 to 35°C, and has
a positive displacement type recirculating pump (2) with a 1 1/min liquid
flow rate. The heating/cooling portion of the bath is modified by adding a
proportional temperature controller No. 71 (3) and control dial manufactured
by RFL Industries, Boonton, New Jersey 07005. The electronic components of
the controller are somewhat temperature sensitive. By mounting the con-
troller on a block of aluminum through which water circulates, temperature
stability is achieved. The water returns to the bath through tube (4). For
temperature control at or near 25° C, approximately 30 volts is supplied to
the heater (5) at all times to "buck" the effect of the refrigerated cooler
(6) and cooler coils (7) which are on at all times. The temperature con-
troller applies varying smaller voltages in response to the platinum sensor
(8). If the need for additional water circulation in the tank is indicated,
a motorized stirrer (9) should be added.
Water from the constant temperature bath flows through rubber tubing to
one or more water-jacketed, large-bore glass condensers (10). The glass
condensers are at a constant temperature and keep the airstream moving
through them at a constant temperature too. Keep the length of tubing used
to supply water to a minimum. The straight condenser (Liebig or West type)
houses the permeation tube (11) and the glass thermometer (12). The ther-
mometer gives the temperature of the air and the permeation tube. An NBS
45
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SWEEP AIR FROM
CLEAN AIR
SUPPLY
CALIBRATION MANIFOLD
VENT
SAMPLING LINE
TO ANALYZER
1 LITER VOLUME
MIXING BULB
Components are described by number in the text.
Figure 3.4. Example of custom-made laboratory permeation tube assembly
for calibration of S02 analyzers.
-------
Catalytic
Converter
Iron-Constantan
Sensor
Heater
\
Temperature
Readout
Proportional
Temperature
•Controller
(Temp. Set for
315° C; 600° F)
Vent (Avoids Pressure Buildup
"" if Valves are Closed Downstream)
Critical Orifice
200 ml/min
Air Bleed
ShutofT
Valve
Pressure
Regulator
Pressure
Gauge
Drierite
• Purafil
o
Shutoff
Valve
Permapure.
Dryer
Pressure
* Regulator
Two Stage
Pressure
Regulator
Oil-less
Compressor •
Pump
Canister of Activated
Charcoal and Filter
f
Mass Flow
Controller
->- Air
Out for
Zero or
Dilution
T
Ambient
Air In
Air Out to
Permeation
Tube System
Figure 3.5. Laboratory clean air supply.
47
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certified thermometer or one traceable to NBS standards should be employed.
A useful thermometer is one having a range of 24 to 25° C in 0.005° C divi-
sions, since many commercial as well as NBS S02 permeation tubes are cer-
tified and used over the range 20-30°C. The all glass thermometer may be
placed in the same compartment as the permeation tube. The water flows- from
the condenser to a sealed glass cylinder (13). Attached to the cylinder is
a stainless steel thermocouple well (14) and, within the well, a platinum
sensor (8). Water leaves the glass cylinder, goes through an aluminum block
beneath the temperature controller, and then returns to the bath.
Air from the laboratory clean air supply enters the bath through a
length of 6.3 mm (1/4 in.) o.d. copper tubing (15). Approximately I meter
(3 feet) of the tubing is coiled and submerged beneath the water of the
bath. The coil serves as a heat exchange element to bring the flushing or
carrier air to nearly the same temperature as the permeation tube. Appro-
priate fittings connect the copper tube to the clean air supply and to a
precision needle valve (16). The needle valve connects to a precision
rotameter (17) having a flow range between zero and 500 cc/minute. The air
then enters one end of the water jacketed condenser. The condenser has been
modified so that the air will be at the temperature of the permeation tube
when it enters the permeation tube compartment. This modification (18)
consists of a short length of 0.25 inch o.d. glass tube attached to a 3 inch
length of coiled 3.2 mm (1/8 in.) o.d. glass tubing. All of the coiled
glass is surrounded by water. The air then flows across the permeation tube
and exits the condenser via either a standard taper ground glass connector
(19) or a ball and socket joint. Connected to the glass fitting is a length
of 6.3 mm (1/4 in.) o.d. corrugated or conventional, straight-walled Teflon
tubing (20). Air containing S02 flows through this tubing to a mixing flask
at which point it combines with diluent air to produce the desired low
concentration of S02.
All of the water and air lines associated with this system are wrapped
in sponge rubber insulation (21) to maintain temperature stability. The
glass condensers are also wrapped in sponge rubber.
Flow across the permeation tube is adjusted to approximately 200
cc/min. Flow is maintained at all times unless the tube is removed.
48
-------
Attention should be given to the air supply used with the laboratory
system. Ambient levels of 02 (20.94%) and C02 (-350 ppm) should be present
in both the flushing or carrier air and the diluent or zero air. The air
supply system shown in Figure 3.5 is designed to run continuously. The
source of air should be "outside" ambient air to ensure that 02 and C02
levels in the calibration gas are equivalent to those levels in the actual
"outside" sample air.
3.4.2 Commercial Systems Employing Permeation Tubes or Devices
Many brands and types of S02-producing "calibrators" are available
commercially. All of them depend on control of the temperature of the
permeation tube or device and control of the flow of air across the tube and
the flow of diluent air in order to produce a known final concentration of
S02 in air within the calibration manifold. Figure 3.6 is a schematic of
the components of a typical calibrator intended for S02 production only.
Figure 3.7 is a schematic of a more elaborate calibrator system intended for
multi-pollutant calibration work. Refer to Section 3.2 for further dis-
cussion of zero air supplies for calibrators intended for use with FPD S02
analyzers.
The temperature of the permeation tube or device is set and controlled
in one of several ways. Some systems employ a small recirculating water
bath. Many systems have a thermostatted "air bath" in which the permeation
device holder is mounted. Others employ heated metal blocks. Whatever the
system, it is important that the temperature be known and controllable to
±0,1° C since the permeation rate of a tube or device is extremely sensitive
to temperature (see Table 3.2).
The flow of air across the permeation device as well as the flow of
diluent air is regulated in one or more of several ways. The simplest
systems have a rotameter and an adjustable needle valve to set and control
the air flows. Such rotameters must be calibrated and checked frequently.
A rotameter should be calibrated "in-line," that is, while it is an in-
stalled part of the system, and not separate from the calibration system.
Do not rely solely on a "calibration curve" for the rotameter. Use a soap
film flowmeter or wet test meter to check flows. More sophisticated systems
employ critical orifices or long lengths of stainless steel capillary tubing
49
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SAMPLE LINE
TO ANALYZER
;
•
(
\
IV
ROTAMETER F
MIXING
FLASK
en
o
CAPILLARY
RESTRICTOR'
PRESSURE
REGULATOR
CALIBRATION MANIFOLD
AND SAMPLE OUTLETS
VENT
HEATED PERMEATION
CHAMBER
PRESSURE
RELIEF
VALVE
s AMBIENT
\AIRINLET
PISTON COMPRESSOR PUMP.
OIL-LESS, TEFLON-LINED
FILTER CONTAINING
ACTIVATED CHARCOAL
ANDPARTICULATE
SCRUBBER
NEEDLE
VALVE
•EXCESS WATER DRAIN
Figure 3.6. Schematic diagram of a portable S02 calibrator with internal air supply.
-------
Chamber Air
Scrubber
Permeation
Tube Holder
Manifold
Connection
Air Supply
Inlet
C7I
UOOL
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
oooc
3-Way
Valve
Instrument
Outlet
3-Way
Teflon
Solenoid
Valve
Chamber
Rotameter
& Control
Permeation Oven
Chamber
Vent
#1 Dilution
Rotameter
& Control
3-Way
Teflon
Solenoid
Valve
#2 Dilution
Rotameter
& Control
ooou
oooo
oooo
oooo
oooo
ooo~
oooo
oooo
oooo
oooc
oooc
oooc
oooc
oooc
3-Way
Valve
Overflow Vent
to Outside
Dilution
Scrubber
Figure 3.7. Schematic diagram of multipoTlutant calibrator. (Adapted from
Metronics Association, Inc. "Dynacalibrator").
-------
to control air flow. Oftentimes regulators and pressure dials are present
so that flow can be re-established by "dialing in" a certain pressure on the
capillary tube or a network of tubes. Even with these systems, calibration
and frequent checks of air flow versus pressure setting are necessary. Some
calibrators have mass flow controllers which can be set to deliver pre-
determined mass flows of air. Since mass flowmeters are not infallible,
they too must be calibrated or verified and rechecked periodically. Mass
flowmeters often exhibit a temperature sensitivity; thus it is important
to operate them at controlled, reproducible temperatures.
All flow measurements taken must be corrected to standard conditions of
pressure and temperature: 760 mm Hg and 25°C for air pollution work. If a
soap film flowmeter or wet test meter is used, do not neglect to correct for
the effect of water vapor (explained in Section 5, Procedural Aids) since
the calibration air is usually quite dry and picks up water vapor while a
flow is being established.
The following features are recommended for consideration in a commer-
cial S02 "calibrator" which employs a permeation tube or device.
1. The presence of a means for temperature control and verification. Some
"calibrators" have a fixed, unchangeable temperature. If temperature
can be varied, a thumbwheel or digital system for accurately setting
and resetting temperatures should be present. A device (such as flash-
ing light or meter/needles) should be present to indicate when the
desired temperature has been attained or when the desired temperature
is not present. Attainment of the temperature of course does not mean
that the permeation tube or device has also attained equilibrium.
Generally, an additional 24 to 48 hours should be allowed for permea-
tion tube equilibrium.
Ideally, an accurate thermometer or thermistor should be embedded in
the permeation tube compartment so that any temperature variations can
be read directly. This thermometer or thermistor should be installed
in such a way that upon removal and replacement, it is seated in ex-
actly the same geometrical configuration. In other words, it should be
impossible for the operator to re-install the thermometer or thermistor
in any way except the correct way. If a temperature sensing device is
not included, the calibrator should have some way to allow the operator
52
-------
to reproducibly place a temperature measuring device in the vicinity of
the permeation device.
2. The permeation tube or device should be easily inserted and removed.
Connections to the permeation tube holder should be leak-tight and
easily retightened and repositioned. All lines downstream of the
permeation tube oven should be of Teflon or glass construction.
3. Air flow controllers and indicators should be of the highest quality
and be capable of being set reproducibly. For instance, pressure
gauges should have accurately divided fine graduations and rotameters
should be of sufficient length (12 inches preferred) to give good
resolution in reading.
4. For field use in calibration of ambient air monitors, the "portability
option" is highly recommended. This option permits a car battery to
supply power to the "calibrator" to keep the oven warm and equilibrated
and to run a small pump to allow continuous passage of air over the
permeation tube or device. If such an option is not used, it is neces-
sary to either remove the permeation tube or purge the system for some
time before use since the high concentrations of S02 which have built
up will be released slowly from Teflon components. It is also, of
course, necessary to re-equilibrate the permeation tube or device at
the desired temperature. While the permeation tube or device is warm-
ing up (equilibrating), a flow of air should pass over the tube or
device.
5. For field use, an internal source of air is desirable. Usually a small
diaphragm or bellows pump is employed. This does away with the neces-
sity of providing an external air source and gives a reproducible
source of air from site to site. Certain precautions must be taken
when using such an air supply. Necessary scrubbers and filters must be
changed periodically. The 02 and C02 content of the air produced must
be characterized and be maintained near the values for ambient air.
Provisions must be included for drying the air and venting any excess
moisture buildup caused by compression of air by the pump. The flow of
air from such internal sources must be stable. The best systems employ
differential pressure regulators. Such regulators can give very stable
53
-------
flow and can be used with internal air supplies or external air sup-
plies such as compressed air cylinders.
6. Since the "calibrator" is often used as a source of zero air, it is
recommended that some sort of zero air by-pass loop be present. In
this way the permeation tube compartment is either by-passed or its
effluent is flushed.
7. The possibility for use of an NBS Standard Reference Material permea-
tion tube in the calibrator should be considered. Not all calibrators
offer this feature since other permeation tubes or devices are either
of smaller dimensions than NBS tubes or operate at higher temperatures
than those specified for NBS tubes. If your calibrator does not have
this feature, it is recommended that a line of traceability of your
system to another system which does use an NBS tube be established.
Also, permeation tubes or devices may be purchased which are traceable
to NBS Standard Reference Materials.
8. The possible range of S02 concentrations and the range of air flows
desired is also a consideration. Various S02 analyzers require differ-
ent sample flow rates.
3.4.3 Explanation of Use of Permeation Device Calibration Systems
The instructions listed below can be applied to most permeation device
type calibration systems for S02. Use the operation manual for your par-
ticular calibrator in conjunction with these instructions and explanations.
1. Unpack and inspect the calibrator. Always perform an inspection if the
calibrator has been shipped to a new location. Inspect the apparatus
(especially the flowmeters and needle valves) for shipping damage.
Look inside the case for evidence of broken or loose mixing tees or
bulbs, loose electronic boards, etc.
2. Make electrical connections. First, be sure that all power switches
are in the "off" position or "stand by" position. Connect the power
switch to a 115V AC socket using a grounded 3-prong plug. Turn the
main power switch to "on" and check the following: internal air supply
pump is on; the fan for air circulation is on and the fan blades spin
freely; the heater for the permeation tube bath or oven is on. This
should be indicated by a temperature light or dial. Turn off the main
power.
54
-------
3- Connect the air supply to the calibrator. If the calibrator has its
own internal zero air supply, connect the inlet of the air supply pump
to the station sampling manifold so that ambient air is treated by the
cleanup system. If a separate air supply system is used, connect its
inlet to an outdoor ambient air source. Do not use room air since rt
will nave a high C02 concentration. See Sections 3.2 and 3.6.3 for
discussion of zero air supplies and the C02 interference effect.
4. Install the permeation tube or permeation device. Your commercial
calibrator unit's operations manual will list the sizes and types of
permeation devices which may be used. Before unpacking the permeation
tube or device, have the calibrator and the clean air supply on and
have a flow of air (about 100 cc/min or greater) passing through the
permeation tube holder. Under dust-free and oil-free conditions,
remove the permeation device from its shipping container in a venti-
lated area, preferably a fume hood. Immediately transfer the tube to
the permeation holder of your calibrator and seal it in. If the per-
meation device has been stored under refrigeration, allow at least 24
hours equilibration time in the case of NBS tubes and longer times with
other devices. Note that some manufacturers do not recommend storage
of permeation devices at low temperature.
It is most important to properly seal the permeation holder. If "0"
rings or other sealing devices are used, be careful not to misalign
them. Threaded Teflon parts must be tightened carefully to avoid
leaks. Avoid stripping the threads. Teflon tape may be used to insure
a good seal. Even a small leak in the permeation tube compartment will
cause a dramatic change in concentration output since relatively high
concentrations of S02 are present prior to dilution. Place the permea-
tion tube (or tubes) in the holder in such a way that the tube does not
obstruct entry or exit of sweep air.
5. Allow sufficient warmup time for oven and permeation device. Install
the permeation device in its holder, set the temperature controller to
the point recommended or desired for use with the permeation device,
and allow the oven to warmup at least 12-14 hours; 24 hours is better.
Allow the permeation tube or device to equilibrate 24 to 72 hours
55
-------
depending on initial conditions and type of device. Maintain a flow of
clean air through the permeation chamber during this time. Consult the
manufacturer's literature for specific recommendations. Once the oven
and permeation tube are equilibrated it is recommended that the system
remain "on" or in "standby" and that air be flushed across the permea-
tion device continuously.
The actual temperature of the operating permeation tube must be known
with certainty. The calibrator should be equipped with an accurate
(preferably NBS - traceable) temperature indicator of some kind - a
thermometer, thermocouple or thermistor. Thermistors or thermocouples
may be purchased and installed in most calibrators. Such devices may
be purchased from Omega Engineering, Inc., Stamford, Conn. , 06907.
6. Set and verify flows. The calibrator will have a needle valve or
pressure regulator or perhaps a mass flow controller to control the
diluent air flow. With rotameters, the position of the ball indicates
the flow. By convention, scale readings are usually taken at the
center of the ball. If your calibrator employs rotameters, a calibra-
tion curve will be provided by the manufacturer. This curve should
have been established under or related to the normal conditions of
25° C and 760 mm Hg.
When used to measure air flow rates, the main variable in rotameters is
density. Assuming that the air is dry after passage through the filter
and scrubber assembly, it is only necessary to correct the indicated
flow for temperature and pressure effects.
At an altitude of 1.5 km (5000 ft), a rotameter will read about 9% low
as compared to sea level. A reading at 25° C instead of 0° C will
cause the rotameter to read 5% low. Because the effects depend on a
variety of factors, it is recommended that for precise work you prepare
your own calibration curve. Use displacement techniques (soap film
flowmeter, wet test meter, etc.) and correct for the effect of water
vapor. These same techniques should be used to verify the flow rate on
mass flowmeters and pressure regulator-orifice systems.
7- Interface the calibration system with the FPD SO? analyzer. Disconnect
the FPD analyzer's Teflon ambient air sampling line from the station
56
-------
ambient air sampling manifold and connect it to the calibration sys-
tem's manifold. Be certain to supply excess sample flow through the
calibration manifold to prevent dilution of the calibration gas by room
air. About 500 cc/min excess (0.5 liters/rain) is suggested as a mini-
mum. Thus, if the instrument's sample flow rate is 250 cc/min, the
overall flow from the calibrator should be at least 0.75 to 1.0
liter/min. Use only cleaned Teflon or glass materials to construct the
calibration manifold. All excess calibration gas should be vented.
Refer to Figures 3.6 and 3.7.
8- Provide zero air to the analyzer. By having the diluent air bypass the
permeation tube compartment or by venting the permeation compartment
contents, zero air is supplied to the analyzer. Allow sufficient time
for a stable zero trace to be established. Set the analyzer to the
desired zero point (refer to Section 4).
9. Provide span gas and intermediate concentrations of S02 to the
analyzer. By adjusting the total flow (usually only the diluent air)
different concentrations of S02 can be generated. The concentration of
S02 at various flow rates can be computed from equations given in Sec-
tion 3.4.4. Remember that the flows should be checked by displacement
methods (soap film flowmeter or wet test meter) from time to time.
Rotameters, pressure gauges, and mass flowmeters are subject to error
and variation and need periodic verification. Also check the flow at
the output of the calibration manifold to detect possible leaks in the
calibration system.
Always remember that S02 is a hazardous pollutant. Do not expose
yourself to the calibration gas; do provide a wel1-ventilated work
environment. All excess calibration gas should be vented. This may be
done by connecting the calibration manifold to the station sampling
manifold exhaust. Use large diameter tubing; avoid high vacuum ex-
hausts.
10. Shutdown and maintenance. If the calibrator is shut down for any
length of time, the permeation tube or device should be removed and
stored in a desiccated container. The main areas for maintenance of
calibrators are: replacement of scrubber materials (such as silica gel
57
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and activated charcoal) on a time-of-use basis; cleanliness of valves
and rotameters; verification of correct operation of heaters and
temperature sensors; verification of correctness of flow and temper-
ature measuring devices.
3.4.4 Computation of S02 Concentrations From Permeation Tubes
The output of a permeation tube or device is converted to concentration
in parts per million (ppm) using the following equation:
r = (R) (MV)
(F) (MW)
where: C = Concentration in ppm by volume at 25° C and 1 atmosphere
(760 mm Hg)
R = Permeation rate, micrograms/minute (pg/min)
MV = Molar volume (24.45 liters at standard conditions of 25° C
and 760 mm Hg)
F = Total flow rate of air (purge air plus diluent air),
liters/minute (at standard conditions of 25° C and 760 mm Hg)
MW = Molecular weight of the permeating gas (MW S02 = 64).
Example Calculation A - What is the ppm output of NBS permeation tube
33-64 (see Table 3.1) under the following calibration conditions?
Permeation tube oven temperature: 22.5° C
Purge air flow rate by soap film flow rate measurement: 180
cc/min
Dilution air flow rate by soap film flowmeter measurement: 4500
cc/min
Room air temperature: 28.0° C
Barometric pressure: 750 mm Hg
Step 1: determine the permeation rate, R, at 22.5° C using the equation
given in Table 3.1.
LOG R = M(273.15 + t) - B
LOG R = 0.033759 (273.15 + 22.5) - 9.97634
LOG R = 0.004508
From a table of five-place common logarithms:
ANTILOG of 0.004508 = 1.010 micrograms/minute = R
58
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Step 2: determine the total air flow and correct it to the conditions
25° C and 760 mm Hg.
Total air flow = 180 + 4500 = 4680 cc/min
= 4.680 liters/minute
Apply this equation to convert the measured flow to the standard con-
ditions of 25° C and 760 mm Hg pressure (refer to section 5.0 for an
example):
298.15
where:
FS = Flow rate at standard conditions in liters/minute
F = Measured total flow rate of air carrying S02 from the
calibrator, liters/minute
P = Barometric pressure in mm Hg (inches of mercury may also
be used provided 29.92 inches of mercury is used in the
denominator, replacing 760 mm Hg)
P1 = Vapor pressure of water, mm Hg (or inches Hg if P is
measured in inches Hg) at temperature t (refer to table
in section 5 or to a handbook of tables). This correction
is made only when a soap film flowmeter or wet test meter
is employed. Assuming the relative humidity of the metered
air is 100%, this corrects for the vapor pressure of water.
t = Temperature of the calibration air in degrees C (or the room
air temperature of the laboratory).
Thus:
750 - 28.35 298.15
= 4.680 x
F = 4.400 liters/minute
C =
(F) (MW)
(1.010)(24.45) _ (1.010 ug/min)(24.45 ul/umole)
(4.400)(64) (4.400 l/min)(64
C = 0.088 (Jl/l or 0.088 ppm
Example Calculation B - What is the concentration of S02 expressed as
micrograms/standard cubic meter (|jg/sm3) at the conditions given in
Example Calculation A?
59
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Use this equation: Cm = R_ x 1000
where:
C = Concentration, jjg/sm3
Thus:
c = 1.010 Hfl/mlnute 1000 v 3 = 229.5
m 4.400 liters/minute
Cm = 229.5 |jg/sm3
Or, since 1 ppm S02 = 2615 ug/m3 at normal temperature and pressure
(25° C, 760 mm Hg), then:
0.088 ppm x 2615 ug/m3 = 230 ug/m3
3.5 CALIBRATION BY USE OF COMPRESSED GAS CYLINDERS CONTAINING S02 IN
NITROGEN OR AIR
3.5.1 General
At present, the permeation tube is the most reliable and accurate
source of S02 calibration gas. However, recent advances in compressed gas
technology have made available special treated cylinders of S02 in air or
nitrogen at high (50-500 ppm) or low (<1-10 ppm) concentrations. For ex-
ample, the National Bureau of Standards has produced four primary standard
S02 in N2 mixtures intended for use in the calibration of instruments used
in the analysis of sulfur dioxide in stack gases. These mixtures have been
shown to be stable for long periods of time (certified for one year) when
packaged in treated aluminum cylinders. Because the NBS Standard Reference
Materials mentioned above are at high concentration levels (480 to 2521 ppm)
and are diluted by nitrogen instead of air, they are not useful for cali-
bration of ambient air FPD analyzers. NBS is, however, studying the sta-
bility of cylinders containing lower (50 ppm or less) concentrations of S02
in air. This study may result in a new Standard Reference Material.
Today, several specialty gas producers supply mixtures of S02 in air at
concentrations ranging down to ambient levels. The higher level mixtures
(100 ppm) have been found to be quite stable,20'21 and can be diluted with
60
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clean air to ambient levels for use. Cylinders of 10 ppm (or less) S02 in
air have also exhibited temperature and pressure stability with no appre-
ciable decay in mixture concentration in one study.20 However, recent field
use of similar mixtures has revealed that low levels of S02 in air (usually
below 50 ppm) in cylinders are not always stable and tend to decay in a
short period of time.22 This decay is illustrated in Figure 3.8.
Due to such concentration uncertainties, cylinders containing very low,
ambient level S02 concentrations in air (i.e., less than 50 ppm) are not
recommended for general calibration use at this time. They are useful for
audits if standardized prior to and after field use and an accounting is
made of any decay in concentration. The higher concentration S02 in air
cylinders (50-100 ppm and greater) are useful for calibrations and audits
and a list of good practices and procedures for their use is given below.
It is recommended that the cylinder's concentration be established by com-
parison to an NBS S02 permeation tube system (i.e., establish traceability).
3.5.2 Equipment Specifications and Use
SO 9 Cylinder. At the present time, the most stable mixtures of S02 in
air or nitrogen have been prepared in treated aluminum cylinders. Conven-
tional steel cylinders are not acceptable. CGA valve outlets vary. NBS
treated aluminum cylinders have CGA 350 outlets; other tanks have CGA 330 or
660 valve outlets.
Cylinders may be shipped and stored in the same way as any other which
contains a toxic gas. If the cylinder has been shipped or stored under
temperature conditions very much different from those inside the laboratory
or air monitoring station where it will be used, an equilibration step is
required. The cylinder is placed in the laboratory or station at least 24
to 48 hours prior to use. It is a good idea to let the cylinder, the at-
tached regulator, and any dilution assemblies equilibrate in the sampling
station at least overnight, under even the best of conditions.
Regulator for SO, Cylinder. The regulator should be a high purity,
corrosion-resistant, stainless steel model with the correct CGA fitting.
Further specifications are:
Diaphragm constructed of type 316 stainless steel or other non-
corroding metal; seals and seats of Teflon or Kel-F.
61
-------
en
ro
oc
o
CJ
CM
o
00
10 -
2 = -1.9 D + 82.1
r =-0.9903
10
12
14
16
18
20
22
24
26
28
30
32
DAY (D)
Figure 3.8. Concentration of SOa versus time. Low-level S02 in air;
treated aluminum cylinder.22
-------
Two stage regulator preferred over one stage.
Pressure gauges should be as small as possible with ranges of 0 to
3000 and -30 to 100 psig.
Regulator should be equipped with a purge assembly option. The
diaphragm of the regulator should be fully supported to permit
evacuation of the regulator without damage to the diaphragm.
Examples of acceptable regulators include Matheson's Series 3800 two
stage stainless steel regulator, Airco's Model 52 and Model 57 series, and
Linde's Model UP-G. Other manufacturers offer similar equipment. This
regulator should be dedicated for use only with S02 mixtures. Furthermore,
an individual regulator should be used only with cylinders of approximately
the same concentrations. For example, a regulator used to deliver 100 ppm
concentrations should not be used to deliver much higher levels (such as
2500 ppm). To do so may cause a buildup of S02 on internal regulator parts
which would require lengthy purging prior to re-use with lower concentration
cylinders.
Dilution Assembly and Clean Air Source. Many commercial units are
available which can dilute a small flow of S02 with clean air. A system may
also be built. Such systems may employ limiting orifices or capillary
networks to achieve a steady, low flow of S02. Passage of S02 mixtures
through a rotameter is not recommended because S02 may be removed on its
surfaces.
The air supplied to the dilution assembly should be regulated so that a
series of known flow rates can be obtained. This is accomplished with
needle valves, critical orifices, capillary tubes, or a mass flow con-
troller. Clean air supplied to a flame photometric detector should contain
ambient levels of C02.
The flow rates of both the S02 and the clean air should be determined
with a calibrated soap film flowmeter or other calibrated meter. The final
concentration is established based on the corrected flow rates.
Assembly of Components. Figure 3.9 shows a suggested layout for
assembly of the cylinder, clean air supply, mixing devices and manifold.
The arrangement is quite similar to that employed in permeation tube sys-
tems.
63
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cr>
Cylinder
Containing
100 ppm
or
Greater
S02 in
Air
Stainless Steel, High Purity
Corrosion Resistant Regulator
Stainless Steel Regulator Outlet
i Valve (metal bellows toggle valve
with Teflon seat recommended)
Precision Regulator
for Critical Pressure
Adjustment
Short Length of Teflon
or Stainless Steel Tubing
Regulated Flow Clean
Air Supply and/or
Dilution Assembly
Purge Port
and Shutoff
Valve
Box Containing Flow
Limiting Orifice or
Capillary (may be
included in commercial
dilution assembly)
Excess
, ^ Sample
I ^ Vent to
Outside Air
Ambient Air In
.Sampling Line
to Analyzer
Glass Mixing
Bulbs 150 cc
Volume
Glass Calibration Manifold with
Unused Ports Capped
S02ln
Dilution
Air In
Detail of Glass Mixing Bulb
Figure 3.9. Assembly for dilution of 862 from cylinder for use
in calibration or span check.
-------
3.5.3 Guidelines for Use of SO, Dilution Systems
1. Allow the cylinder, attached regulator, and dilution assembly to equil-
ibrate in the laboratory for 24-48 hours prior to use so that tempera-
ture equilibrium is reached.
2. During this equilibrium period, the tank's regulator should be thor-
oughly flushed and conditioned with S02. It is important to remove any
gaseous or surface adhering water from the internal parts to avoid S02
removal. If the regulator is "wet," its effect on S02 concentration
will be noted by a slowly increasing signal response on the continuous
S02 analyzer. To expedite the removal of water, the purge assembly of
the regulator is used in one or both of the following ways.
a. Pressurization/Evacuation
(1) Attach a small vacuum pump to the purge assembly fitting.
Close the purge assembly valve. Close the regulator outlet
valve.
(2) Open the cylinder valve and pressurize the regulator. Adjust
the regulator control valve to pressurize the low pressure
gauge. Close the cylinder valve.
(3) Turn on the pump, open the purge assembly valve and pull a
vacuum on the regulator for 1 minute. The low pressure gauge
should read a negative value. Close the purge assembly
valve.
(4) Repeat the pressurization/evacuation procedure 4 or 5 times.
Remove the pump, and pressurize the regulator with the S02
mixture. Close the cylinder valve until ready for use.
b. Purge with dry air or nitrogen
Attach a cylinder of clean, very dry, nitrogen or air to the purge
port. Open the purge port valve and regulator outlet valve.
Allow a low flow of gas to purge through the regulator for 20-30
minutes.
After the regulator has been purged and conditioned, it should be left
attached to the S02 cylinder, and filled with the S02 mixture. If it must
be removed, the regulator may be protected from moisture by immediately
capping or plugging the CGA outlet and closing all valves.
65
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3. The concentration of a new cylinder of S02 in air (or nitrogen) should
be re-established prior to actual field use by comparing its outlet to
that of a permeation type calibration system whose permeation tube or
device is an NBS Standard Reference Material or is traceable to an NBS
permeation tube. An experienced person should conduct or oversee this
operation.
This is done by first calibrating a continuous S02 analyzer with a
permeation tube system. Next the diluted gas from the S02 cylinder is
sampled by the analyzer and, after stabilization of the signal, the
concentration value is recorded. If a FPD analyzer is used, the air
supplied to the permeation tube calibrator and the dilution assembly
must have the same C02 content as the outside ambient air. Since the
dilution factor is known, the tank concentration can be calculated and
compared to the manufacturer's analysis. If the value so obtained is
significantly lower than that stated on the cylinder, first check the
dilution system for leaks or interferences to S02 detectability. If no
fault is found, it is probable that the tank S02 level has decayed.
Example calculation:
FL S02 flow rate from tank: 10 cc/minute
F2, Dilution air flow rate: 1420 cc/min
R, Calibrated analyzer response: 0.42 ppm
Thus: [S02], ppm = (R) r*F *
[S02], ppm = (0.42) 142°Q+ 10
[S02], ppm (cylinder) = 60.06
4. The cylinder may now be taken to ambient air monitoring stations for
use as a calibration, span check, or audit device. Dilution air at
each station should be processed ambient air so that the diluent air
contains ambient levels of C02 when FPD analyzers are calibrated.
CAUTION. Allow sufficient time for temperature equilibration of
the cylinder at each monitoring station.
66
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The S02 tank is used for multipoint calibration in much the same way as
the permeation tube. The dilution air flow is varied to give different
concentrations of S02; when the S02 supply line is disconnected or
vented, the dilution air serves as a source of zero air.
5. The concentration stability of such S02 cylinders should be checked
from time to time by returning the cylinder to a central laboratory for
redetermination of its concentration by comparison to an NBS permeation
system. This should be done at least quarterly for long-term studies
and monthly for shorter term efforts. Replace the tank when the pres-
1 sure reaches 500 psig.
3.6 OTHER FACTORS AFFECTING THE S02 OUTPUT FROM DYNAMIC CALIBRATION
SYSTEMS AND/OR THE RESPONSE OF FPD S02 ANALYZERS
3.6.1 Temperature at Which the Permeation Tube is Used
The temperature at which the permeation tube is used must be precisely
known and controlled to within ±0.1° C of the value selected. Knowledge of
the correct temperature is very important since the permeation rate of tubes
increases (or decreases) in a logarithmic fashion with change in tempera-
tures. Table 3.2 illustrates the errors that are introduced for a typical
tube when the temperature is unknowingly varied from an assumed value of
25.0° C.
3.6.2 Air Flow Rate and Clean Air Supply
The rate of air flow (cc/minute or liters/minute) across the permeation
device must be known. This is established by calibration of the dilution
air flow rate with a soap film flowmeter, wet test meter, or an air mass
flowmeter. Each of these measuring devices must itself have been recently
calibrated and referenced to an NBS traceable standard of volume.19 See
Section 5 for a discussion of the use and calibration of air flow measuring
devices. Many calibration systems split the clean air supply and send a
small portion of the flow over the permeation device and a large portion to
combine with the S02-laden air coming from the permeation tube compartment.
The gases leaving the permeation tube compartment contain S02 at relatively
high levels. A small change in the flow rate across the tube would not
affect the final concentration significantly since it would be small com-
pared to the total flow. However, a ]eak in the permeation tube compartment
67
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Table 3.2. Typical errors due to temperature variation
of an S02 permeation tube
Temperature
°C
25.0
25.1
25.5
26.0
27.0
Permeation Rate
|jg/minute
2.62
2.64
2.72
2.83
3.05
Concentration *
at 760 mm, 25° C Error1
(Dilution at 12 liters/minute) Percent
|jg/m3
218
220
227
236
255
ppm
0.083
0.084
0.087
0.090
0.097
0
1
4
8
17
Assuming the operator thought the temperature was at 25.0°C and was
attempting to obtain 0.083 ppm S02
or in the lines leading to the dilution air would cause a large decrease in
the S02 concentration since S02 at high concentrations would be escaping.
Certain materials such as stainless steel, dirty surfaces, and non-
Teflon filters usually cause a diminishment of S02 by adsorption or reac-
tion. Use only glass or Teflon tubing and Teflon filters in your calibra-
tion system.
An essential part of the calibration system is its supply of clean, dry
S02-free, zero air. This air must be like ambient air in two important
respects: the oxygen and nitrogen content must be the same as ambient air,
and the C02 content should be similar to that in ambient air (300-350 ppm).
The oxygen/nitrogen ratio affects the flame of the FPD, and the presence of
C02 in ambient air will depress the signal if C02 was not present in the
calibration gas.
3.6.3 Carbon Dioxide Interference in the FPD Method for Sulfur Dioxide
3.6.3.1 Nature of the Problem
A problem often encountered with FPD analysis of S02 and associated
calibration procedures is the negative span interference or "quenching"
caused by ambient C02. The best solution to the problem, at present, is to
provide ambient levels of C02 in the calibration gas.
68
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That the problem exists is shown by the results of recent audits23
conducted at various ambient air measuring facilities, Table 3.3.
Part of the variance in response to the audit concentrations can be
attributed to factors other than C02 interference. However, quantitative
examination of the audited calibration system's C02 output often revealed
C02 concentrations much less than ambient levels. Minimization of the C02
interference depends on having ambient levels of C02 present in the calibra-
tion gas.
Carbon dioxide is naturally present in the ambient atmosphere at aver-
age concentrations of 300-350 ppm. There are variations with height, time
of day and season.24 Near sources of C02, concentration variations may be
significantly greater than those of rural ambient air. For instance, at
ground level, near a densely populated and heavily traveled area of a city,
the levels of C02 in air would be higher than that in the countryside.
The C02 does not react with or remove the S02. Its effect on the
signal is probably due to collisional quenching processes which inhibit the
formation of the excited state S2* molecule or deactivate the excited state
S2* molecule prior to chemiluminescent emission.
S2* + C02 *• S2 + C02 (without chemi luminescent emission)
Overall, this results in an apparent lowering of the FPD S02 concentration
output signal, i.e., a negative span interference.
Table 3.4 shows analyzer response results for a modern 1976 model ambi-
ent air S02 FPD analyzer. One set of data was established in the presence
of ambient C02, ~350 ppm, the other in the absence of C02. Note that the
percent response increase at different S02 concentration levels is about the
same, 17%, when the C02 is removed.
All commercially available continuous FPD S02 analyzers show this C02
effect to varying extents (see Table 3.3). The effect is not observed in
analyzers which chromatographically separate S02 from other atmospheric
gases (e.g., C02).
69
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Table 3.3. Evaluation of C02 interference in total
sulfur measurements using FPD analyzers23
S02
Audit
Instrument Concen-
Brand tration
(ppb)
50
A 99
151
51
A 101
150
59
B 103
150
59
B 103
150
50
C 100
150
65
C 127
188
50
D 99
149
49
D 102
151
Measured
0 ppm
C02
(ppb)
51
107
180
49
111
170
53
108
148
53
107
149
45
91
138
61
126
190
46
95
149
40
91
146
TS Concentrations
360 ppm
C02
(ppb)
41
92
149
41
90
142
49
100
142
50
101
145
46
90
135
58
116
174
44
88
135
38
87
132
750 ppm
C02
(ppb)
34
78
129
34
74
119
44
92
135
48
101
140
46
82
114
53
101
150
43
84
126
35
84
131
% Change
0 ppm C02
360 ppm CO
-20%
-14%
-17%
-16%
-19%
-16%
-8%
-7%
-4%
-6%
-6%
-3%
+2%
-1%
-2%
-5%
-8%
-8%
-4%
-7%
-9%
-5%
-4%
-10%
From
Measurement
2 750 ppm C02
-33%
-17%
-28%
-31%
-33%
-30%
-17%
-15%
-9%
-9%
-6%
-6%
+2%
-10%
-17%
-13%
-20%
-21%
-7%
-12%
-15%
-13%
-8%
-10%
70
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Table 3.4. FPD analyzer response, ppm S02) in the
presence and absence of carbon dioxide.
Perm tube
Predicted
S02 , ppm
0.0
0.437
0.338
0.278
0.144
0.099
0.078
Instrument
Response,
Volts
(C02 present/
C02 absent)
0.0135/0.014
0.875/1.032
0.678/0.795
0.540/0.630
0.283/0.335
0.191/0.225
0.149/0.176
Calculated^
S02 , ppm
(C02 present
at 350 ppm)
0.006
0.439
0.340
0.271
0.142
0.096
0.075
Calculated^
S02 , ppm
(C02 absent)
0.007
0.518
0.399
0.316
0.168
0.113
0.088
% Response
Increase,
(C02 absent)
_
18.0
17.3
16.6
15.5
17.7
17.3
Calculated based on least squares regression calibration equation
established in the presence of ~350 ppm C02.
3.6.3.2 Minimization of the C02 Interference
The C02 interference can be minimized by dynamically calibrating the
analyzer with S02 in air mixtures containing ambient levels of C02 (~350
ppm). Then, when the analyzer is returned to ambient air, it will "see"
approximately the same amount of C02 and the effect will be the same as
during calibration. In this way the C02 interference has been "nulled out"
or compensated for by the calibration zero and span adjustments.
It should be noted that calibration and rechecks of calibration will
not uncover the presence of a C02 interference. For instance, one might
calibrate with air mixed with S02 containing no C02. The calibration may be
repeated and give excellent agreement with the first calibration. However,
when the analyzer is returned to ambient air, an immediate quenching of the
S02 signal occurs.
Of course, if the concentration of C02 in the air used for calibration
purposes changes dramatically from one calibration to the next, there can be
a noticeable difference between successive calibration span values. This
effect could be mistaken for instrument span drift or calibration gas inac-
curacy.
71
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To ensure that ambient levels of C02 are included in the calibration
gases, a calibration system should be set up which uses on-site outside
ambient air (which is scrubbed free of sulfur compounds but not C02) as a
source of zero and dilution air.
Ambient air, taken from outside the sampling station, must be used and
can be obtained from the station sampling manifold. Do not use room air.
Room air C02 levels may be much higher than those of ambient air. If the
analyzer is calibrated with air containing C02 levels higher than in ambient
air, the response to S02 upon return to ambient air will be greater than
during calibration, resulting in an apparent positive interference.
A zero air generator suitable for FPD zero and calibration work is
shown in Figure 3.1, Section 3.2.1. A laboratory experiment was carried out
to determine the amount of C02 which passes through commonly employed scrub-
bers. A 3.8 x 15 cm (1.5 x 6 inch) cylindrical column contained the scrub-
ber material; flow rate of the air/C02 mixture through the system was 1
liter per minute. Analysis was by gas chromatography. Results are sum-
marized in Table 3.5.
The results show that the S02-scrubbing agent, activated coconut char-
coal, does not retain C02 significantly, especially if it is conditioned
prior to use. The drying agents, "Drierite" (TM) and silica gel, pass C02
quantitatively. Molecular sieves (which are often found in heatless air
dryers) completely remove C02 and should not be used. Soda lime and "As-
carite" (TM) also absorb C02 completely and should not be used as scrubber
material.
Parameters for the operation of individual clean air systems should be
optimized by the user. The dimensions of the scrubber cartridge and the
amount of material packed inside will be dictated by the air flow rate, the
length of time the system is used before repacking the scrubbers, and the
concentration of pollutants present in the ambient air.
Most commercial calibration systems intended for use in calibrating
ambient level FPD S02 monitors will normally have a nominal total air flow
of from 2-5 liters/minute.
3.6.4 Percentage of Oxygen in Calibration Air
The flame photometric detector has been shown to give a varying re-
sponse to S02 when air supplied to the flame has a varying oxygen content.
72
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Table 3.5. Retention of C02 on commonly
employed scrubber materials.
Scrubber material
C02, ppm
prior to scrubber
C02, ppm
after scrubber
Exposure time,
minutes
Activated coconut
charcoal, 6-14 mesh,
taken directly from
new container. 56g.
350
245
88
Activated coconut
charcoal, 6-18 mesh,
conditioned for 16.5
hrs. at 300°C in air.
56g.
350
345
80
"Drierite" (TM),
10-20 mesh.
20g.
350
347
32
Molecular sieves,
Type 5A, 8-12 mesh.
28g.
350
32
Silica gel, indica-
ting, coarse mesh.
67g.
350
350
150
The use of scrubbed ambient air for zero and dilution is recommended in
order to avoid this problem. If cylinder air is used, it should contain the
correct ambient percentage of oxygen (20.94) and nitrogen (78.9). Meatless
air dryers may also slightly alter the oxygen content of ambient air.
Figure 3.10 illustrates the variation in response of an FPD analyzer to
a fixed concentration of S02 diluted by air of varying oxygen content.
3.7 SUMMARY OF FPD S02 CALIBRATION SOURCE PARAMETERS WHICH MUST BE
OPERATOR-CONTROLLED
Table 3.6 presents a checklist of calibration source parameters which
must be operator-controlled in order to obtain valid data from FPD S02
73
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21
20
19
ID
X
o
18
17
16
17
0.0806 ppm (20.94% 02)
18
0.0876 PPM (19.4% 0.
0.0941 PPM (17.73% 0,)
0.10114 PPM (16.18% 0,
19
20
21
22
23
ANALYZER RESPONSE, mv (0-100 mv FULL SCALE)
Figure 3.10. Variation of FPD analyzer response with air oxygen content
at a fixed SOa concentration of 0.0806 ppm.
74
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analyzers. The table lists the parameter, how the operator controls the
parameter, how lack of control can be identified, and how the parameter may
be brought into control.
75
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01
Table 3.6. S02 calibration source parameters which must be operator-controlled
in order to obtain valid data
PARAMETER
Knowledge of the permeation rate of S02 from tube or device
How Operator Controls Parameter
1. Purchase NBS certified S02 permeation tubes; use as received or employ for establishing trace-
ability of other tubes or devices.
2. Purchase other tubes or devices which:
a. Are certified by their manufacturer as being calibrated by use of NBS or NBS- traceable
materials.
b. Can be compared to S02 standard atmospheres generated in your laboratory by use of
NBS permeation tubes.
3. Exercise care in storage, handling, and use of permeation tubes.
How Operator May Identify Lack of Control
The expected output of the tube or device changes with time and no other factor can be identi-
fied (temperature, flow, etc.) which could cause the problem.
The outlet from the tube or device does not agree with the expected value when the calibration
system is compared to another system which uses an NBS certified tube.
The tube contains no visible liquid S02 or is visibly cracked or split, or is visibly oily
or dirty.
How Operator May Bring Parameter Into Control
A defective permeation tube cannot be repaired, it must be replaced.
-------
Table 3.6. S02 calibration source parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Temperature of permeation tube bath or holder
How Operator Controls Parameter
Some commercial permeation tube or device type calibration systems have an adjustable dial or
thumbwheel to set the temperature of the air bath or compartment which contains the permeation
device. Other systems are preset at some temperature (such as 35°C) and cannot be adjusted.
Temperatures in systems employing recirculating water (or other fluid) are set using controls
of the constant temperature water bath.
How Operator May Identify Lack of Control
A small change in the temperature of the permeation tube will cause a change in the concen-
tration of S02 produced. This is one indication of temperature variation. Also check the
thermocouple signal output of the system for indication of drift. Some calibration sources have
a meter which indicates whether temperatures are being controlled or not. Check it.
If it is possible to do so, a thermometer (of NBS or ASTM accuracy) with at least ±0.1°C
graduations should be placed in the permeation tube compartment with the mercury bulb located
next to the permeation tube while air is flowing across the permeation tube. A thermocouple or
thermistor may also be used as a temperature sensor.
How Operator May Bring Parameter Into Control
If heating and cooling devices are unstable or defective, replace them and calibrate the
temperature output with a thermometer or thermocouple/thermistor arrangement. If unable to
calibrate temperatures, compare the system's S02 output to that of an independent S02 source
which has been temperature calibrated and which uses NBS permeation tubes.
If a temperature-adjustable system is operating satisfactorily but is only out of calibra-
tion, make adjustments and recalibrate the system.
-------
Table 3.6. S02 calibration source parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Flow rate of purge air and dilution air
How Operator Controls Parameter
Control is usually by use of resettable pressure regulators and/or rotameters which are coupled
to restrictive capillaries and orifices. Such pressure settings and rotameter readings must
be correlated with actual flow rate by flow calibration.
How Operator May Identify Lack of Control
An increase in total air flow will result in a decrease in S02 concentration.
A decrease in total air flow will result in an increase in S02 concentration.
00
How Operator May Bring Parameter Into Control
First, check the dial settings on the calibration system's pressure gauges and rotameters to
be sure they are at the desired settings. If they are wrong, next check the pressure at the source
of the air supply, tank or compressor. If too low, increase the tank pressure, replace the tank
or correct the compressor problem. Be sure compression pumps are operating.
Second, check the calibration and analyzer system for leaks. Use leak detection solution on
pressurized lines only.
If the pressure gauges or rotameters are simply misadjusted, reset them.
It is most important that no leaks occur in the permeation tube holder since S02 will be
vented in large concentration. By use of a bubble flowmeter, this flow should be established
and rechecked occasionally. This is done by breaking into the line downstream of the permeation
holder. The dilution air flow settings (gauge or rotameter) must also be matched with actual
air flow by calibration with a bubble flowmeter or wet test meter.
Two ways to check for system leaks are suggested: 1. measure flow at the inlet and outlet
and compare; 2. plug the outlet and pressurize the system with air, then use leak detector solution.
-------
Table 3.6. S02 calibration source parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Interferences to S02 concentration or response of FPD analyzer
The major problems are caused by:
1. Use of stainless steel tubing or other tubing besides Teflon or glass (causes loss of S02
and/or slow analyzer response).
2. Water condensation in zero and/or dilution air (causes loss of S02).
3. Wrong 02:N2 ratio in zero and dilution air (causes variability of flame and may increase
or decrease response to S02).
4. Zero or less than ambient amounts of C02 in the zero and/or dilution air (causes an apparent
diminishment in S02 concentration when analyzer is returned to ambient air).
5. Pressurization of the S02 calibration manifold.
How Operator Controls Parameter
1. Use only Teflon or glass to deliver S02 to analyzer.
2. Provide air free of condensation by use of scrubbers, or in the case of compressed ambient
air, provide route for excess liquid water to escape from compression chamber.
3. Use S02-free ambient air where possible. If compressed cylinder air is used, specify that
it be ambient compressed air. If synthetic air (prepared from 02 + N2)is used, request an
analysis of contents. The desired concentrations are: 20.9% 02, 78.9% N2, and 350 ppm C02.
4. Use dry, S02-free ambient air where possible. Air supply system must be such that the ambient
air C02 content is maintained. If compressed air from cylinders is used, ambient C02 levels
(350 ppm) should be present. Analysis for C02 should be requested.
5. Provide restriction-free venting of the calibration manifold. If a vacuum is used at the vent,
be certain it is a light, gentle vacuum which will not cause a partial vacuum to occur within
the calibration manifold.
-------
Table 3.6. S02 calibration source parameters which must be operator-controlled
in order to obtain valid data (continued)
How Operator May Identify Lack of Control
1. Inspect tubing and fittings of calibration systems.
2. Moisture droplets appear in tubing. Moisture scrubber is exhausted. If an indicating drier
is used (such as indicating Drierite or silica gel), the color will change from blue to pink
as it becomes exhausted.
3. A sudden change occurs in instrument response to S02 (increase or decrease) immediately after
attachment of a new source of zero air.
4. Chemically measure the amount of C02 in your zero air at the calibration manifold (see
Section 5 for instructions).
5. Attach a water manometer pressure gauge to one of the calibration manifold outlets. No
pressure or vacuum should register. Momentarily remove any vent lines, etc. and continue
o to sample a known S02 concentration with the FPD. If any change in response occurs, the
presence of the vent tube, etc. must have been causing an effect.
How Operator May Bring Parameter Into Control
1. Replace all tubings, fittings with Teflon and/or glass material.
2. Provide vent or other route for excess water to escape from pressurization system. Add a
water scrubber (such as Drierite or silica gel) to your zero air system; replace exhausted
drying agent.
3. Specify that your zero air contain 20.9%, 78.9% N2, 350 ppm C02.
4. Use a system which does not scrub C02 from ambient air if ambient air is scrubbed and used
as a source of zero air. If compressed cylinder air is used, be sure C02 is part of the mix-
ture (request analysis if necessary).
5. Remove any restrictions to proper venting of the calibration manifold. Use a light,
gentle vacuum at the vent.
CONCLUDED
-------
SECTION 4.0
CALIBRATION OF THE FLAME PHOTOMETRIC DETECTOR FOR S02 IN AMBIENT AIR
4.1 INTRODUCTION TO CALIBRATION
4.1.1 Qualitative and Quantitative Analyses
The qualitative basis for any analytical method is the occurrence of a
change in some property of the analytical system when the compound you wish
to determine is added.
The flame photometric detection of S02 is a qualitative procedure.
When S02 reaches the H2/air flame, processes occur which produce an excited-
state S2 molecule. This molecule loses its excess energy by emitting light,
and this light is sensed by a photomultiplier tube. The amperage signal
from the photomultiplier tube is converted electronically to a voltage
signal, which is displayed on a voltmeter or a stripchart recorder.
It is understood that the analytical method must be specific for the
compound being determined. This is another way of saying the analytical
method for compound A has no positive or negative interferences from compounds
B, C, D, etc. However, in practice, most analytical methods suffer inter-
ferences. Without modification, flame photometry is not specific for S02
detection. When burned in a hydrogen-rich flame, any sulfur-containing gas
may produce the excited-state S2 molecule, which decays and emits light with
a range of wavelengths centering around 394 nm. To be certain that the
light of other wavelengths does not reach the photomultiplier tube, a 394-nm
narrow band pass optical filter is used. This makes the FPD highly selective
for detection of sulfur-containing compounds. In a further step, the FPD is
made highly specific for S02 by the use of a "scrubber," which removes H2S
from the sample air stream while allowing S02 to pass unaffected. A chroma-
tography column can also separate S02 from unwanted compounds.
A qualitative analysis can become a quantitative analysis. A quantita-
tive analysis is one which not only tells you what compound, but also how
much of that compound is present. To assign a value to an unknown concentra-
81
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tion, the change or response of the analytical system to the unknown is
compared to predetermined responses obtained for a sample containing none of
the compound (known as a blank or zero) and a series of samples of known
concentration. The concentrations which are known have been previously
established by another analytical method. This set of known concentrations
is sometimes called a set of standards. The process of obtaining the analyt-
ical system's responses for the members of a set of standards is often
called standardization of the analytical method. Another term describing
this process is calibration.
4.1.2 Definition of Calibration; Requirements for Calibration
In general terms, calibration is the process of precisely relating the
magnitude (size) of the response of the analytical system to the concentra-
tion of the compound being measured. To achieve a valid calibration, two
major requirements must be met.
1. The response of the analytical method to different concentrations
of standard should be as reproducible and unvarying as possible.
This is achieved by careful control of parameters affecting re-
sponse. Furthermore, the effects of any interferences on response
must be accounted for.
2. The concentration of the compound used as a standard for calibra-
tion must be known with a high degree of accuracy. This degree of
accuracy must be within the limits of sensitivity of the analytical
method. The standards must be sampled by the analytical method in
the same way that unknown samples are taken.
To meet these two major requirements, careful control of parameters
affecting the calibration standards (discussed in Section 3.0) and the
analytical method (discussed in this section) must be maintained.
The meaning of the word "calibration" as applied to an automated analyzer
such as the FPD S02 must be clearly understood. Calibration for automated
methods refers to a complete multipoint characterization of the analyzer's
response to an accurate, reliable standard over the entire analyzer range.
A "zero and span operation" consists of a baseline check with clean air and
a one-point check of analyzer response. Zero and span is not an acceptable
basis for calibration.
82
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An FPD S02 analyzer should be calibrated on-site upon installation and
at intervals thereafter. Monthly calibrations are suggested; calibration
every 2 weeks may be best in some cases. Zero and span checks should be
performed more frequently-daily if possible. These procedures, along with
maintenance and preventive maintenance are important parts of an air-monitoring
system's quality control program and are essential in maintaining the accuracy
and reliability of air quality data.
It is important that the FPD analyzer be operated during calibration
under conditions identical to those in its normal ambient air sampling mode
of operation. No modifications or alterations should be made to the ana-
lyzer's components, flow system, prescribed flow rate, or other parameters.
Concentrations of S02 intended for calibration must be generated continuously
by means entirely independent of the analyzer. The flow rate of the calibra-
tion gas must exceed the sample flow rate of the analyzer. The calibration
gas should flow through a manifold and the analyzer should draw its sample
through the regular ambient air sampling line, which is attached to a port
of the vented calibration manifold.
This section of the TAD covers more than just a procedure for multipoint
calibration of an FPD analyzer. Also included are suggested steps for
station maintenance and recordkeeping, how to conduct a zero and span check,
a short section on maintenance and replacement operations, and a checklist
of FPD analyzer parameters and their control.
The procedure for multipoint calibration of an FPD analyzer is neces-
sarily general. Where analyzer-specific instructions or explanations are
necessary, the reader is referred to supplementary information located at
the end of the procedure and to the manufacturer's instruction manual.
Special explanatory and precautionary material in the text is set apart
by being enclosed in blocks.
4.1.3. Recordkeeping
A permanent record should be kept on all activities relating to calibra-
tion and maintenance of the FPD analyzer. The date and time intervals should
be clearly noted. Also keep records on such items as: maintenance of cali-
bration devices, calibration gases, hydrogen supplies, other analyzers, and
the monitoring station itself. Also, record your name in the notebook, on
the stripchart, etc.
83
-------
A hardbound laboratory notebook is highly recommended. Make legible
entries in ink; cross through erroneous entries with a single line. Many
users find calibration and maintenance forms useful since they remind the
operator to perform certain steps. If such forms are used, a copy should be
pasted or taped into the notebook along with calibration curves and equations.
The stripchart record should also be marked. A short description of
the action taken should be given. Times should be noted and marked clearly
with a line or arrow.
4.2 PRELIMINARY STEPS
Before calibrating the FPD S02 analyzer, certain preliminary steps are
taken. All of these steps are carried out before any adjustments are made
to the analyzer, the calibration system, the data recording system, or other
laboratory equipment serving the analyzer. In this way, any changes that
have occurred in the total analytical system since the last calibration or
check can be recognized and recorded. By examining this record over a
period of time, problems of the analyzer (such as varying sample flow rate),
the calibrator (such as temperature drift), or the station environment (such
as inadequate temperature control) can be recognized and corrected.
1. Survey station condition. Check temperature/humidity control,
cleanliness of station ambient air inlet, etc. Record findings in
station logbook.
2. FPD Analyzer online, warmed up. Before calibrating an FPD ana-
lyzer, the electronics and flame should have been on (sampling
mode) for at least 24 hours.
If this is an initial calibration of a new instrument, a
good practice is to test the analyzer for 5 to 7 days
while conducting an accelerated program of zero, span,
and multipoint calibrations. In other words, during
this first week, calibrate the instrument about three
times and carefully compare results from one calibration
to the next to detect sources of error or drift, which
need correction prior to recording ambient air data.
3. Calibration system online, warmed up. If a calibration system
employing a permeation tube or device is to be used, the following
steps must be completed before calibration begins:
84
-------
The permeation tube or device must have been installed in its
compartment and the constant temperature air or water bath
must have been in operation at the desired temperature for at
least 24 to 48 hours if the tube or device is initially at a
temperature 10° C different from that of the oven. If its
temperature is only 1° or 2° C different from that of the
oven, 3 hours of equilibration time may be adequate. Shorter
or longer times may be required and these times can only be
deduced by experience. During equilibration a low flow of
clean air (sweep air) must pass over the permeation device.
Without this air flow, large concentrations of S02 will build
up in the permeation compartment and lengthy purging with
clean air will be necessary.
The source of clean, S02-free air (used for zero air, sweep
air, and diluent air) must be in a state of readiness. If
heated scrubbers (such as catalytic oxidizers) are used, such
devices should be powered, warmed up, and producing clean air
prior to use with the calibrator. Spent cartridges of chemi-
cal scrubbers should be replaced with equivalent materials,
dirty filters should be replaced and conditioned, and water
condensation traps should be emptied. Dirty or sticking
rotameters should be disassembled and cleaned, dried, reassem-
bled, and recalibrated. It is easier to perform such mainte-
nance in the central laboratory rather than at the field
site. Record all maintenance activities in the station
logbook or in a notebook devoted to the calibration system.
NOTE: Following any maintenance or replace-
ment activities on the calibration system, it
is important to:
(1) Double check all connections for air
leaks.
(2) Check the zero air output from the system
to be certain that the new chemical
scrubbers are not off-gasing any sulfur-
containing compounds. In other words,
85
-------
does the FPD signal increase dramatically
on "zero" air after the scrubbers are re-
placed? If it does, the scrubber packing
or holder is contaminated and must be re-
placed.
(3) Compare +he instrument response to the
zero air produced by the new scrubber
system with the response to zero air from
the previous scrubber system. If the
response is significantly lower for the
new scrubber than for the old, this
indicates that the old scrubber system
was exhausted and was allowing SO^ to
pass. Record any significant variations
and make a report to the data validation
section since some prior data may need to
be voided.
(4) Be certain that the flow rates of zero,
sweep, and diluent air have not been
altered. Redetermine flow rates if
necessary.
d.
The relation between the settings of rotameters or pressure
dials of the calibration system and the flow rate of dilution
air and permeation tube sweep air should be established by
calibration of the air flow with a wet-test meter or soap
film flowmeter. See Section 5 for an explanation of the use
of these devices. All measured flow rates should be corrected
to standard temperature and pressure conditions, 25° C, 760
mm Hg. See Section 5 for the procedure for correcting air
flow rates to STP.
If the permeation tube has not been used for some time,
examine it visually to be sure liquid S02 is still present.
Order calibrated permeation tubes or devices in plenty of
time to provide replacement. As long as 4 months may be
required to receive an NBS-certified permeation tube. See
Section 3 for information concerning permeation tubes and
devices.
86
-------
Determine any time discrepancy between the recorder and the
local time. Over a period of days, the recorder drive mecha-
nism may lag behind or speed up with respect to local time.
This could be due to power failure, an inaccurate chart drive
mechanism, or to Hnding, or slippage of the chart paper on
the drive mechanism. Note the time discrepancy in the station
logbook, determine its cause, and take corrective action.
Remove the stripchart roll and examine the ambient air trace
(and any automatic zero or span checks) for the previous 24
hours. Look for evidence of power failure, flameout and
automatic reignition, unusually high values, unusually low
values (such as a straight zero baseline), and noisy signals.
Such information is helpful in determining the
present status of the analyzer and will indi-
cate whether further warmup time is necessary
before calibration. The stripchart roll
should be clearly marked with the station
number and inclusive times and dates and
forwarded to the person responsible for data
analysis.
Check the ink supply of the recorder. Add ink and clean the
system as necessary. Replace the stripchart roll with a new
one. Move the paper and start the pen at the desired time
mark, and record the station name, date, and time on the
stripchart.
If a data acquisition system (DAS) is being used, remove the
magnetic tape cartridge and insert a new one. Some operators
may prefer to leave the old tape in place, recording data,
until the multipoint calibration is complete. Others may
prefer to have the new calibration data entered on the new
tape. If the calibration data are entered on the new tape,
later application of the calibration equation to the raw data
points acquired during calibration should give the correct
calibration values if the scan or integrating interval of the
88
-------
DAS is short enough. This serves as a check on the integrity
of the data acquisition system and the computer program,
which treats the raw data.
Always take adequate notes of time on, time
off, any analyzer response scale changes made,
periods of calibration, etc. See that these
notes reach the person responsible for magne-
tic tape data workup and interpretation so
that signal variations due to calibration,
zero, span, power failures, etc., are recog-
nized and not confused with ambient air data.
6. Connect the stripchart recorder to analyzer. If a recorder is not
already in place, connect one to the analyzer. Be sure the range
of the recorder matches that of the analyzer output. It is recom-
mended that the recorder baseline be offset to create a live zero
for instruments having both positive and negative signal output.
This is done by calibrating the recorder so a zero voltage input
corresponds to 5 percent of the full-scale chart (i.e., 5 chart
divisions if the paper has 100 divisions). A digital voltmeter
may also be connected at this time. This will also permit the
identification of negative zero drifts during calibration.
A good practice is to use shielded cables to make
signal connections. Consult the recorder manufac-
turer's manual for instructions. Since the recorder
trace is often used as the permanent record for the
data, the operator must be aware of the potential
for error by problems such as:
a. Recorder "dead band" error,
b. Noisy trace due to improper gain adjustment,
c. Loading error caused by the recorder and/or
the voltmeter, and
d. Erroneously set zero and span points.
89
-------
Recorders and voltmeters should be carefully checked and cali-
brated to avoid such errors. Refer any questions or problems to
an experienced electronics technician. Records should be kept of
recorder and voltmeter calibrations and adjustments or repairs.
Preventive maintenance programs should include recorders, data
acquisition systems, and electronic measurement devices.
7. Obtain station temperature and pressure. In order to correct any
measured volumetric flow rates to standard temperature (25° C) and
pressure (760 mm Hg or 29.92 in. Hg), the temperature of the cali-
bration air sample and the barometric pressure at the site must be
known.
The temperature of the calibration gas is best determined by in-
serting a precision-grade glass thermometer into the calibration
manifold. Once a steady temperature is attained, record the value
and remove the thermometer. The room air temperature of the
station may also be used, but it is possibly a less accurate
reading than that taken directly from the manifold.
The atmospheric pressure is best obtained by reading a mercury
column barometer or aneroid barometer which is located in the
sampling station and has been in place long enough to achieve
temperature equilibrium. Refer to Section 5 for instruction in
the use and reading of barometers.
The nearest airport that maintains atmospheric pressure data may
be called for information. Be sure that you ask for the actual
"station pressure," not the pressure used by aviators, which has
been corrected to sea level.
EXAMPLE. A call was placed to the local airport
weather service on March 22. The recorded an-
nouncement stated the pressure was 29.60 in. Hg at
2:00 p.m. This is the value for aviators.
According to the meterologist on duty, the actual
station pressure at 2:00 p.m. was 29.185 in. Hg.
This latter value is the one to be used in volu-
metric correction equations.
90
-------
The pressure at a site may be approximated by reference to a table
listing barometric pressure at various altitudes. The elevation
of the site must be known. See Table 4.1.
EXAMPLE. An ambient air sampling station is lo-
cated at an altitude of 2,058 feet above sea level.
What is the average pressure at the site in mm Hg?
From Table 4.1, Psite = 27.70 + .02 = 27.72 in. Hg
(25.4 mm/inch) (27.72 in. Hg) = 704 mm Hg.
Be aware that significant temperature and pressure changes can
occur during the timeframe of a calibration. If a barometer is
present in the station, a reading should also be recorded at the
conclusion of the calibration. A significant change may explain
minor variations in instrument response since the instrument
sampling rate is not mass-flow controlled.
4.3 ZERO AND SPAN CHECK
A zero and span check consists of a determination of an analyzer's
baseline response to clean air and to a single S02 span point. In this way,
certain analyzer malfunctions and drift that occur between calibrations may
be detected. A zero and span check should be conducted daily if possible
and just prior to a multipoint calibration. Only slight adjustments should
be made to the zero pot; no adjustments should be made to the span pot. A
zero and span check should not be confused with a multipoint calibration.
Zero and span data should not be used as a basis for data workup. Zero and
span data are very useful to help an operator keep track of daily zero and
span drifts. In contrast to a multipoint calibration, a zero and span check
uses only two points and perhaps uses a less accurate, less reliable, or
nondynamic S02 standard.
Often a zero air source is included within the analyzer. Zero air is
supplied by having the analyzer's sample pump pull air through a charcoal-
filled cartridge. By activating a solenoid valve, the air sample is pulled
through the cartridge rather than through the ambient air sample line.
Thus, the path of the built-in zero air is not the same as that followed by
ambient air. The span gas may also enter by a path other than that used for
91
-------
Table 4.1. Barometric pressure at various altitudes.
Barometric
pressure, B
inches
23.50
.60
.70
.80
.90
24.00
.10
.20
.30
.40
24.50
.60
.70
.80
.90
25.00
.10
.20
.30
.40
25.50
.60
.70
.80
.90
26.00
.10
.20
.30
.40
26.50
.60
.70
.80
.90
27.00
.10
.20
.30
.40
27.50
.60
.70
.80
.90
28.00
.10
.20
.30
.40
28.50
.60
.70
.80
.90
29.00
.10
.20
.30
.40
29.50
.60
.70
.80
.90
30.00
.10
.20
.30
.40
30.50
.60
.70
.80
0
Feet
6,546
6,431
6,316
6,202
6,088
5,974
5,861
5,749
5,637
5,525
5,414
5,303
5,193
5,083
4,974
4,865
4,756
4,648
4,540
4,433
4,326
4,220
4,114
4,009
3,903
3,799
3,694
3,590
3,487
3,384
3,281
3,179
3,077
2,975
2,874
2,773
2,672
2,572
2,473
2,373
2,274
2,176
2,077
1,980
1,872
1,784
1,688
1,591
1,495
1,399
1,303
1,208
1,113
1,019
925
831
737
644
551
458
366
274
182
91
0
-91
-181
-271
-361
-451
-540
-629
-718
-806
0.01
Feet
6,535
6,420
6,305
6,190
6,076
5,963
5,850
5,737
5,625
5,514
5,403
5,292
5,182
5,072
4,963
4,854
4,745
4,637
4,530
4,423
4,316
4,209
4,104
3,998
3,893
3,788
3,684
3,580
3,477
3,373
3,270 •
3,168
3,066
2,965
2,864
2,763
2,662
2,562
2,463
2,363
2.264
2,166
2,067
1,970
1,872
1,775
1,678
1,581
1,485
1,389
1,294
1,199
1,104
1,009
915
821
728
635
542
449
357
265
173
+82
-9
-100
-190
-280
-370
-460
-549
-638
-727
-815
0.02
Feet
6,523
6,408
6,293
6,179
6,065
5,952
5,839
5,726
5,614
5,503
5,392
5,281
5,171
5,061
4,952
4,843
4,735
4,627
4,519
4,412
4,305
4,199
4,093
3,988
3,882
3,778
3,674
3,570
3,466
3,363
3,260
3,158
3,056
2,955
2,854
2,753
2,652
2,552
2,453
2,353
2,254
2,156
2,058
1,960
1,862
1,765
1,668
1,572
1,476
1,380
1,284
1,189
1,094
1,000
906
812
718
625
532
440
348
256
164
+73
-18
-109
-199
-289
-379
-469
-558
-647
-735
-824
0.03
Feti
6,512
6,397
6,282
6,167
6,054
5,940
5,827
5,715
5,603
5,492
5,381
5,270
5,160
5,050
4,941
4,832
4,724
4,616
4,508
4,401
4,295
4,188
4,082
3,977
3,872
3,767
3,663
3,559
3,456
3,353
3,250
3,148
3,046
2,945
2,843
2,743
2,642
2,542
2,443
2,343
2,245
2,146
2,048
1,950
1,852
1,755
1,659
1,562
1,466
1,370
1,275
1.180
1,085
990
896
803
709
616
523
431
338
247
155
+64
-27
-118
-208
-298
-388
-478
-567
-656
-744
-833
0.04
Feet
6,500
6,385
6,270
6,156
6,042
5,929
5,816
5,704
5,593
5,480
5,369
5,259
5,149
5,039
4,930
4,821
4,713
4,605
4,498
4,391
4,284
4,178
4,072
3,966
3,861
3,757
3,653
3,549
3,446
3,343
3,240
3,138
3,036
2,934
2,833
2,733
2,632
2,532
2,433
2,334
2,235
2,136
2,038
1,940
1,843
1,746
1,649
1,552
1,456
1,361
1,265
1,170
1,075
981
887
794
700
607
514
421
329
237
146
+ 55
-36
-127
-217
-307
-397
-486
-576
-665
-753
-841
0.05
Feet
6,489
6,374
6,259
6,145
6,031
5,918
5,805
5,693
5,581
5,469
5,358
5,248
5,138
5,028
4,919
4,810
4,702
4,594
4,487
4,380
4,273
4,167
4,061
3,956
3,851
3,746
3,642
3,539
3,435
3,332
3,230
3,128
3,026
2,924
2,823
2,723
2,622
2,522
2,423
2,324
2,225
2,126
2,028
1,930
1,833
1,736
1,639
1,543
1,447
1,351
1,256
1,161
1,066
972
878
784
690
597
505
412
320
228
137
+45
-45
-136
-226
-316
-406
-495
-585
-673
-762
-850
0.06
Feet
6,477
6,362
6,247
6,133
6,020
5,906
5,794
5,681
5,570
5,458
5,347
5,237
5,127
5,017
4,908
4,800
4,691
4,584
4,476
4,369
4,263
4,156
4,051
3,945
3,841
3,736
3,632
3,528
3,425
3,322
3,219
3,117
3,016
2,914
2,813
2,713
2,612
2,512
2,413
2,314
2,215
2.116
2,018
1,921
1,823
1,726
1,630
1,533
1,437
1,342
1,246
1,151
1,057
962
868
775
681
588
495
403
311
219
128
+36
-55
-145
-235
-325
-415
-504
-593
-682
-771
-859
0.07
Feet
6,466
6,351
6,236
6,122
6,008
5,895
5,782
5,670
5,558
5,447
5,336
5,226
5,116
5,006
4,897
4,789
4,681
4,573
4,465
4,358
4,252
4,146
4,040
3,935
3,830
3,726
3,622
3,518
3,415
3,312
3,209
3,107
3,005
2,904
2,803
2,703
2,602
2,502
2,403
2,304
2,205
2,107
2,009
1,911
1,814
1,717
1,620
1,524
1,428
1,332
1,237
1,142
1,047
953
859
765
672
579
486
394
302
210
118
+27
-64
-154
-244
-334
-424
-513
-602
-691
-780
-868
0.08
Feet
6,454
6,339
6,225
6,110
5,997
5,884
5,771
5,659
5,547
5.436
5,325
5,215
5,105
4,995
4,886
4,778
4,070
4,562
4,455
4,348
4,241
4,135
4,030
3,924
3,820
3,715
3,611
3,508
3,404
3,301
3,199
3,097
2,995
2,894
2,793
2,692
2,592
2,493
2,393
2,294
2,195
2,097
1,999
1,901
1,804
1,707
1,610
1,514
1,418
1,322
1,227
1,132
1,038
943
849
756
663
570
477
384
292
201
109
+18
-73
-163
-253
-343
-433
-522
-611
-700
-788
-877
0.09
Feet
6,443
6,328
6,213
6,099
5,986
5,872
5,760
5,648
5,536
5,425
5,314
5,204
5,094
4,985
4,876
4,767
4,659
4,551
4,444
4,337
4,231
4,125
4,019
3,914
3,809
3,705
3,601
3,497
3,394
3,291
3,189
3,087
2,985
2,884
2,783
2,682
2,582
2,483
2,383
2,284
2,185
2,087
1,989
1,891
1,794
1,697
1,601
1,504
1,408
1,313
1,218
1,123
1,028
934
840
746
653
560
468
375
283
192
100
+9
-82
-172
-262
-352
-442
-531
-620
-709
-797
-885
92
-------
ambient air. The source of the span gas may be a tank or other single-point
S02 supply. The analyzer may have a programmable clock wired to solenoid
valves so that zero and span operations occur at preset times without the
need for operator assistance.
It is possible to set up a dynamic calibration system which will supply
zero air and one or two span concentrations to the ambient air sampling line
at preset intervals. At least one manufacturer (Metronics) offers such a
system.
Suggested steps and explanations for performing zero and span opera-
tions are listed below.
1. Zero check. Manually or automatically switch the analyzer sample
control (if the analyzer is so equipped) to the zero position.
Mark the stripchart with time, date, and action. Enter the same
information in the notebook. If the zero point is entered auto-
matically in the operator's absence, be sure to note later the
date, duration, etc., on the stripchart and in the station logbook.
Be sure that the person ultimately responsible for data reduction
and analysis is made aware of these operations so that such time
intervals are accounted for. If an automatic data acquisition
system is used, be sure that it does not treat the zero and span
readings as ambient data.
Allow sufficient time for a stable zero signal to occur. If the
system is automated, program the clock for ample time. If the
zero air source requires warmup, allow time for this, too. Make
no adjustments to the analyzer at this time.
NOTE. The system used for the multipoint calibra-
tion may also serve as a zero and span source.
First, be certain the system is warmed up and flows
are calibrated. Then connect the analyzer to the
calibration manifold in the same way as in a multi-
point calibration.
Such a zero and span operation is often performed
just prior to a multipoint calibration. In this
way, changes in analyzer response since the last
93
-------
__ ___ ^_ __ __^ ,.„.„,_ _. _„, ^^ -_T_ -,—, ^_ ^.i,,, I,— _ •• "|
[multipoint calibration are determined by an accurate,
[ reliable, dynamic calibration source. |
2- Span check(s). Set up the span gas supply so that an accurately
known concentration of approximately 80 percent of full scale is
generated. Turn on the single-point span gas supply by manual or
automatic means. Mark the stripchart and enter time, date, and
action in the notebook.
Follow all the manufacturer's instructions for installation and use of
the span gas source. Allow sufficient time for the span gas supply to
equilibrate and for the response of the analyzer to stabilize. With auto-
mated systems, program the clock for ample time. Make no adjustments to the
analyzer.
NOTE. The system used for the multipoint calibration
may also serve as a span check source. If possible, the
same span concentration as used during the last multi-
point calibration should be generated so a direct com-
parison can be made. If this cannot be done, the con-
centration that is generated should be compared to the
expected value (or voltage) based on the calibration
curve or calibration equation established for the most
recent prior calibration. This comparison could be made
by: (1) solving the least squares regression equation
for the expected response (mv, volts, or chart divisions)
to the known S02 span concentration you are generating,
or (2) finding the expected response on a carefully
drawn calibration graph of the analyzer response versus
S02 concentration.
3. Disconnect the zero and span system. Be certain that the analyzer
ceases to sample zero or span gas and is returned to ambient air.
When the span check ends, allow sufficient time for the analyzer
response to "recover" from the span signal. This will be evident
from the stripchart trace. The time at which recovery is complete
should be recorded as the "end time" for zero and span operation.
This will also be the time at which valid ambient air data are
94
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again recorded. Denoting this time is particularly important when
an automatic data acquisition system is used.
4- Correct problems indicated by zero, span data. As a general rule,
no adjustments are made to the zero and span settings of an ana-
lyzer during a zero and span check. This is because of several
reasons. The zero or span source is often not as accurate as the
dynamic calibration system. Minor variations (noise) in instru-
ment zero and span response are expected and cannot be adjusted
out. Large changes in atmospheric pressure or C02 levels of
cleaned ambient air can affect the span signal somewhat and daily
adjustment cannot compensate for this.
If gross variations (greater than 5 percent, the percent allowable
drift for an EPA equivalent-designated instrument) are noted in
either the zero or span check, or if the zero or span is slowly
but steadily changing in one direction over a period of days,
action should be taken. First, check the zero and span sources
for reliability by comparison to calibration standards or by
performing a dynamic calibration. If they are correct, the ana-
lyzer itself needs corrective maintenance and a multipoint cali-
bration.
4.4 MAINTENANCE AND REPLACEMENT OPERATIONS
Following the zero and span check and just prior to a multipoint dy-
namic calibration, maintenance and replacement activities are carried out.
Any maintenance on the station itself (such as air conditioning adjustment
or cleaning of ambient air intake) is also done at this time. A record of
all items replaced or adjustments made should be entered in an appropriate
notebook or logbook. A supply of replacement gases, filters, and parts
should be maintained at the central laboratory.
It is suggested that the following minor maintenance and replacement
steps be performed prior to each monthly multipoint calibration. Special
conditions such as dusty environments may necessitate more frequent main-
tenance.
1. Check gas supplies. Replace empty or near-empty gas cylinders of
hydrogen, air, or others. Service H2 generators by adding water
95
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or electrolyte. Refer to the manufacturer's instruction manual.
If the FPD analyzer flames-out when the H2 supply is replaced,
relight the flame as soon as possible to avoid long restabili-
zation times.
Check all connections between the H2 supply and the analyzer
to be certain they are leaktight. Use a liquid leak detector.
2. Replace filters; clean or replace sampling lines. Often a Teflon
membrane filter and Teflon filter holder are located in the ambient
air sampling line leading to the analyzer. Some operators make a
practice of replacing this filter prior to each multipoint dynamic
calibration. Do not allow too much particulate matter to build up
on the filter before replacing it. Replace the filter and clean
the holder prior to calibration. Figure 4-1 shows a typical
filter and holder and gives directions for its assembly.
CAUTION. Be sure the Teflon filter is seated
properly and the filter holder is reassembled
tightly. If not, a leak will exist and particles
may reach the FPD burner. Exercise care not to
overtighten Teflon threaded connections. If the
thread are stripped, a poor seal results.
Another filter which may need to be replaced is located at the
rear of the analyzer at the dilution air entry. Replace it with
an identical filter. Some analyzers have a coarse sintered brass
filter located on the pump inside the case. The sintered filter
should be replaced after about 1 year of continuous operation.
CAUTION. The dilution air filter holder is often
attached to a hypodermic needle which pierces a
rubber septum and acts as a critical orifice. This
supplies a constant flow of dilution air to dilute
the moist burner exhaust air and prevent unwanted
water condensation.
If the needle must be removed to replace the filter
holder, be sure it is put back exactly as it was.
Be careful not to obstruct the needle by clogging
it with a piece of rubber septum material. If the
96
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CALIBRATION OR
AMBIENT AIR INLET
10
TEFLON
FILTER
TO ANALYZER
Figure 4.1. Sampling line filter holder and filter of all-Teflon construction,
-------
needle is replaced, the new one should be of exact-
ly the same length and gauge as the old one in
order to avoid large flow changes. If the rubber
septum is cracked or not seated properly, replace
it too.
CAUTION. If the dilution air filter is replaced
with one quite different from the original, flow
changes in both the dilution air and the sample air
may occur. Calibration errors, flameout, and other
problems may also occur.
The ambient air sample line itself, 3.2 mm (1/8 in) o.d. Teflon,
may occasionally need replacement because of a buildup of parti-
cles or occurrence of "kinks" in the line. If so, cut and install
a new piece of exactly the same length as the one it replaces.
Use only Teflon fittings; check all fittings for tightness. Any
new tube or filter will require a conditioning period with S02
before a stable, steady signal is attained.
The lines may also be cleaned by removing them, flushing with pure
methanol (methyl alcohol, a poison), and venting zero air or dry
nitrogen through the tube until it is dry. Recondition the lines
with S02 calibration gas.
3. Leak check. Any pneumatic connections that were untightened
during maintenance and replacement should be leak-checked. Use a
liquid leak detector or pure water. Wipe off the fluid after
testing.
4. Perform other maintenance. Any maintenance or repair of the
stripchart recorder and the data acquisition system should be done
at this time.
5. Adjust instrument flow rates.
a. Carefully adjust the hydrogen flow rate control knob. Hydro-
gen flow will be indicated by a pressure gauge or rotameter
or both. Set the gauge or rotameter to the position speci-
fied in the operating manual. Record both the old and new
settings in notebook.
98
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b. Carefully adjust the air sample flow rate control knob. Some
analyzers, such as the Meloy Model 285 and the Monitor Labs
Model 8450 have preset sample flow rates which cannot be
adjusted. Sample flow will be indicated by a rotameter, but
usually only when the analyzer is in the zero mode. Set the
rotameter to the manufacturer's suggested setting. Determine
the actual ambient mode flow rate by attaching the analyzer
sampling line to the upper part of a soap film flowmeter.
Refer to Section 5 for explanation of use. Record the flow
value in the notebook.
Any major maintenance on the FPD analyzer should be done prior to cali-
bration. Be sure to allow enough time for the analyzer to warm up again
before beginning calibration. Consult the manufacturer's instruction manual
for details of major maintenance operations. Major maintenance items include:
1. Sample pump overhaul or replacement,
2. Photomultiplier tube replacement,
3. Solenoid valve replacement,
4. H2S scrubber replacement or reconditioning,
5. Cleaning or replacement of rotameters or gauges,
6. Cleaning of the burner block, and
7. Cleaning or replacement of the cooling fans.
4.5 MULTIPOINT CALIBRATION OF AN FPD S02 ANALYZER EQUIPPED WITH
A LINEARIZED OUTPUT
A multipoint calibration must be performed when the analyzer is first
set up and periodically thereafter. The frequency of calibration will de-
pend upon the type of sample the analyzer receives, the environmental condi-
tions under which the analyzer operates, and the requirements for data
accuracy. Only by performing frequent calibrations (at least monthly) can
the reliability and accuracy of air quality data be maintained and assessed.
Dramatic changes in calibration results alert the user to problems with the
analyzer or calibrator. Periodic calibrations are an important part of the
quality control and quality assurance aspects of an air monitoring program.
The following procedure is intended for use with instruments that are
designed to sample the ambient atmosphere for S02. Under these conditions,
99
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the S02 level often will be low (often 0.1 ppm or less) and measurements of
the highest accuracy are sought. To help insure the accuracy of the data,
the analyzer should be operated under controlled environmental conditions of
temperature, voltage, and humidity, and the calibration procedure should be
performed frequently.
A multipoint calibration should be performed soon after receipt of a
new analyzer and monthly thereafter. In addition, a multipoint calibration
should be carried out:
1. Following any adjustments or replacements of amplifier assemblies,
power supply boards, temperature control boards, or photomulti-
plier tube;
2. If for any reason the air sample flow rate or hydrogen flow rate
is adjusted from previously set or recommended values (these flows
affect the flame and, thus, affect the response); and
3. If the burner assembly or any Teflon lines are cleaned or re-
placed.
A dynamic calibration should always be performed at the site of the
analyzer. Do not calibrate an instrument at one location, move it to another,
and expect the calibration to "hold."
Step-by-step instructions for dynamic calibration of a typical FPD S02
analyzer (using the linearized output) are given below. Each step is numbered.
Special explanations or precautions are given immediately following the in-
structions. Figure 4.2 is a reproduction of the stripchart trace of a
typical multipoint calibration and should be consulted as one proceeds with
the calibration.
1. Verify that PRELIMINARY STEPS. ZERO AND SPAN CHECK. AND MAINTENANCE
AND REPLACEMENT steps are complete. Record all actions and results
in a notebook or the calibration logbook.
2. Interface the analyzer and the calibration system. Disconnect the
analyzer's Teflon ambient air sampling line from the station
ambient air sampling manifold and connect it to the calibration
system manifold.
The ambient air sampling line should be used for
calibration purposes. In this way the calibration
100
n
ion
-------
TIME MARK
1700 EST
RETURN TO AMBIENT AIR
^_ ENTER 6TH CALIBRATION
1 -POINT (0.075 PPM)
ENTER 5TH CALIBRATION
POINT (0.1 SO PPM]
ENTER 4TH CALIBRATION
POINT (0.225 PPM)
STABILIZATION
PERIOD
CALIBRATION
POINT
I 10.375 PPMI
~ ENTER SPAN GAS AGAIN (0.400 PPM)
MAKE MINOR ZERO ADJUSTMENT
SPAN GAS
STABILIZATION
PERIOD
ENTER SPAN GAS (0,400 PPM SOj)
INDICATES APPROXIMATE POINT IN TIME TO READ
STRIP CHART AND DVM; RECORD VALUES
X^ I ADJUST ANALYZER ZERO POT
READINGS AT THESE POINTS ARE USED TO CONSTRUCT
CALIBRATION CURVE AND TO DERIVE THE LEAST
SQUARES REGRESSION EQUATION OF THE CALIBRATION
LINE
ZERO AIR
STABILIZATION
PERIOD
NOTE: CHART SPEED IS 6 INCHES/HOUR
ENTER ZERO AIR (0.000 PPM S02>
j
AMBIENT AIR {-
TIME MARK
1600 EST '
VOLTS
0.460
0.90
Figure 4.2. Calibration trace of linearized output.
FPD ambient air S02 analyzer.
101
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gas passes through the same pathway (including the
Teflon particulate filter) as the ambient air and
the same pressures and flow rates are maintained.
Do not change the length of the Teflon sampling
line.
Use of other zero or span gas entry ports to the
instrument is not recommended for multipoint cali-
bration. Use such ports only for zero and span
checks.
3. Sample zero air. Leave the analyzer in the sample mode and allow
it to sample zero air from the calibration manifold until a stable
reading on the stripchart trace or voltmeter is obtained. Record
the voltage reading or stripchart reading (number of divisions or
percent of full scale) in the notebook. Compare the zero gas
reading to the value set at the previous calibration. The values
should be nearly the same if no significant zero drift has occurred.
Do not adjust zero pot at this time.
Be certain that your zero air meets all require-
ments for zero air. It should not contain sulfur
compounds or large amounts of water vapor. It
should contain = 350 ppm (or ambient levels of)
C02. The oxygen/nitrogen percentage composition
must be the same as in ambient air. Refer to
Section 3.0 for a discussion of the carbon dioxide
effect and the composition of zero air.
The zero airflow must be in excess of the analyzer
sample flow demand, preferably 50 percent greater.
Thus, if an analyzer's sample flow is 200 cmVmin,
the zero airflow must be at least 300 cmVmin.
Do not pressurize the calibration manifold since
this will alter the analyzer's response. See
Figure 3.6 or 3.7 for an illustration of correct
installation of a calibration manifold. Provide
unobstructed exhaust of excess air. Do not allow
back diffusion of room air. The pressure (as
measured at the calibration manifold) must not
exceed 1 inch of water, either positive or negative,
102
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from the ambient pressure. Use a water manometer
for measuring pressure. Refer to Section 5.0 for
instructions on its use.
As long as 30 minutes or more may be required to
obtain a stable zero baseline. This is usually the
case when a high S02 concentration has been sampled
just prior to sampling zero air. The analyzer
should have been on for at least 24 hours prior to
calibration.
Set the zero of the analyzer. Set the front panel zero adjust pot
so that the analyzer output, as measured by the digital voltmeter,
DVM, reads 0.000 V or the value given by the manufacturer for the
linearized output. (For example: 0.000 V for Monitor Labs Model
8450; 0.014 volts for Meloy Labs Model SA-185-2A.) Do not set
zero by adjusting the recorder zero.
PRECAUTION! If your FPD S02 analyzer is a model
8300 manufactured by the Bendix Corporation, do not
adjust the front panel zero adjust. Internal
adjustments of the nonsulfur suppression pot may be
required. Refer to the Bendix operation manual for
assistance or see Section 4.6.1 for procedures and
explanations. Calibration of Bendix FPD analyzers
continues with Step 5.
If your analyzer is manufactured by Meloy Labora-
tories and you wish to use the log output instead
of the linearized output, refer to Section 4.6.2
for further details. Instructions for offsetting
zero of Meloy instruments are given in Section
4.6.3.
The pen of the stripchart recorder should trace a line at the
point on the chart paper corresponding to 0.000 V (or the voltage
value assigned to zero ppm S02)- Stripchart divisions, percent of
103
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full scale chart readings, or ppm S02 values taken from the re-
corder may be used instead of voltmeter readings. Be certain the
recorder itself is properly zeroed, spanned, and its response is
linear. See Figure 4.2 for an example of voltage and ppm S02
readings assigned to a stripchart.
Allow a few minutes following zero pot adjustment to be sure a
stable voltage is obtained, then "lock" the zero pot and record
the voltage value in notebook.
Sometimes the process of "locking" the zero pot
causes a slight change in the setting. Be aware of
this and make necessary adjustments.
If an unusually large adjustment is necessary, or
if the zero point cannot be set by adjustment of
the pot:
a. Be sure the analyzer has been given sufficient
time to stabilize on zero air (check strip
chart for no further change in slope of the
trace).
b. Be sure there is no source of S02 or other
sulfur compound entering the zero air.
c. Be sure the charcoal scrubber for the zero air
supply is fresh.
d. Be sure the flame is lighted.
e. Consult manual or manufacturer for trouble-
shooting and servicing procedures.
5. Sample SQ9 span gas. Adjust the flow rate of the calibration
assembly to produce an S02 span gas of concentration equal to
approximately 80 percent of the value of the analyzer's range.
The usual ranges used are 0 to 0.5 or 0 to 1.0 ppm. If, for
example, the analyzer is set to a 0-0.5 ppm range, 80 percent of
the range would be (0.80) (0.5) =0.4 ppm. Generate this concen-
tration (0.400 ppm) or an accurately known value close to it. Use
104
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this as the span gas concentration. Instructions are given in
Section 3.0. Sample the span gas until a stable signal is obtained
(as indicated by the stripchart trace). Record the voltage value
or stripchart reading in the notebook as "unadjusted span" value.
A permeation tube type calibrator, whose tube is
traceable to NBS standards, is recommended for
generating all S02 concentrations for span and
intermediate concentrations. Be certain the diluent
air (carrier air) is of the same composition as the
zero air. See Section 3.0 for details of the use
of such calibration devices, calculation of the S02
concentration, and the use of S02 from cylinders as
calibration gases.
Provide a flow of span gas that is at least 50
percent in excess of the analyzer's flow require-
ment.
As long as 30 minutes may be required for signal
stabilization, especially if the analyzer is new or
if new tubing or a new H2S scrubber has been in-
stalled, stabilization may take several hours.
This is due to the "conditioning" of "active sites"
in the Teflon line and scrubber by S02. Usually
10-15 minutes should suffice for stabilization.
If the analyzer response goes "offscale" and does
not soon return, remove the sampling line from the
manifold momentarily and check to see if the ana-
lyzer and recorder are on the correct range. Also,
check the dilution air flow setting of the cali-
brator.
Another cause of offscale readings is excess S02
from a permeation tube that has remained in its
compartment without air passing over it continuous-
ly. If this is the case, the calibrator must be
flushed with clean air for some hours before the
calculated concentration is obtained.
6. Compare "unadjusted span" value to previous calibration results.
Using the previous calibration curve or equation and the "unad-
105
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justed span" reading determined in Step 5, determine the concen-
tration of S02 being indicated by the analyzer. Compare this
result to the calculated span gas concentration being used in Step
5. The calculated concentration is based on the permeation device
output and measured dilution airflow rates. Compute the percent
difference between the two values.
Example calculation. Based on the previous multi-
point calibration curve, the indicated S02 span
concentration is measured as 0.392 ppm. The concen-
tration based on the permeation tube weight loss
and known dilution flow rates, is 0.430 ppm.
Thus:
Indicated Concentration - Calculated Concentration ,„„ ..••*•
x 100 = percent deviation
Calculated Concentration
0.392-0.430 x1nu = -8.84 percent
0.430
If the values are within ±10 percent, proceed to Step 7.
If the present span concentration is greater than ±10 percent of
the value predicted by the previous calibration data, a problem
may exist in the present calibration setup, a problem was present
at the last calibration, or the analyzer has drifted significantly
and needs maintenance. Check the present calibration using the
following steps.
Check the calibration system for:
a. Proper dilution airflow setting (redetermine actual
airflow if necessary and recalculate S02 concen-
tration if an error was made).
b. Sufficient airflow to the analyzer. (50 percent
excess flow is desirable.)
c. Proper temperature and temperature control of
permeation oven.
106
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d. Line voltage variations.
e. Leaks.
f. Permeation tube integrity.
g. Proper C02 content of diluent air.
Check the FPD Analyzer for:
a. Correct and stable sample flow rate.
b. Correct H2 flow rate.
c. Obstruction-free exhaust.
Check the recorder for correct span.
If no fault is found in any of these checks, the
analyzer may need electronic adjustment. Refer to
the manufacturer's manual or consult the manu-
facturer. It is also possible that the previous
calibration was in error; it should be reviewed for
errors.
7. Set the analyzer span. Calculate the expected analyzer voltage
output and/or recorder response (chart divisions or percent of
full scale) for the calculated concentration of span gas. Adjust
the front panel span pot so that the linearized output reads the
correct value on the DVM and/or the stripchart.
Example computation. If the analyzer is set on the
0-0.5 ppm range and has a 0-1 V linearized output,
and the calibration system is set to give 0.400 ppm
S02, the predicted voltage is computed as follows:
calibrator span, ppm
analyzer range, ppm
0.400 ppm
0.500 ppm
analyzer full _ voltage
scale voltage ~ span point
output
I volt = 0.800 V
The recorder should trace a steady line at an
upscale point. If the recorder is on the 0-1 V
range, the stripchart has 100 chart divisions, and
the recorder zero is set at 5 percent of full scale
(i.e., five chart divisions), then 0.400 ppm S02
should give a trace at:
107
-------
x (100 divisions) + (5 divisions) =
80.0 + 5 = 85.0 chart divisions
Refer to Figure 4.2 for illustration.
8. If the span adjustment required in Step 7 was appreciable (±5
percent of the expected value), return the analyzer to zero air
(Step 3), allow the analyzer to stabilize, and make necessary
adjustments of the zero pot.
9. Return to the span gas, allow the analyzer response to stabilize,
and make necessary adjustments of the span pot.
10. Repeat zero and span gas operations until it is no longer necessary
to adjust the zero or span pots.
11. Adjust the calibrator flow rates to generate in succession the
following standard S02 calibration levels (expressed as percent of
instrument range):
approximate percent of range ppm, if 0.5 ppm range
75
60
45
30
15
0.375
0.300
0.225
0.150
0.075
Other levels may be introduced if desired. Values less than 0.100
ppm are suggested since ambient S02 concentrations are usually in
this range. Values less than 0.040 ppm (40 ppb) are very slow to
give a stable response.
Important! Make no adjustments to the zero or span pots while
these points are being entered.
Record the voltage or stripchart response for each level.
108
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Introduction of an S02 concentration equal to
exactly 75 percent, 60 percent, etc. of full scale
range is not necessary. What is important and
necessary is that these concentrations be equally
spaced over the range; be within ±5 percent of the
75 percent, 60 percent, etc., level; and that the
concentration be prepared with accuracy (within
0.001 ppm).
Allow sufficient time for each S02 level to stabi-
lize ("level off" as indicated by the stripchart)
before proceeding to the next value.
The instrument response time and stabilization time
will be slower at the lower concentration values.
12. Construct a plot of the calibration data on graph paper. Refer to
Figure 4.3 as an example.
a. Use a high quality graph paper with fine graduation marks so
that data points may be clearly entered. A good choice is
18 x 25 cm graph paper with 10 x 10 divisions to the centi-
meter.
b. Assign the S02 concentration values to the x-axis (horizontal
axis). These are the calculated values from the calibration
system. Subdivide the x-axis in ppm extending from zero to
the analyzer's full scale range. Units of microgratns of S02
per cubic meter (ug/m3) may also be plotted; 1 ppm S02 =
2,615 ug/m3 S02 at 1 atmosphere (760 mm Hg) and 25° C.
Assign the analyzer response (V or mV or percent of scale) to
the y-axis (vertical axis) and subdivide this axis into
portions of the full scale output for the particular analyzer
(0-1 V, 0-100 mV, etc.).
c. Enter the zero and span values on the graph, also enter all
intermediate calibration values.
d. Check the quality of the calibration curve in the following
way:
With the aid of a straightedge (ruler, etc.) connect the
zero and span points with a light pencil line.
109
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LEAST SQUARES OF LINE OF BEST FIT
LEAST SQUARES LINEAR REGRESSION EQUATION IS:
VOLTAGE = 1.992 [SOjI - 0.0054
[S02],ppm 0.437 0.338 0.278 0.144 0.099 0.078
RESPONSE, VOLTS 0.875 0.686 0.555 0.292 0.198 0.155
0.1
0.2 0.3
S02 CONCENTRATION, PPM (x-AXIS)
0.4
0.5
Figure 4.3. Calibration curve for linearized FPD S02 analyzer.
-------
Look at the positions of the intermediate calibration
points with respect to the straight line. The inter-
mediate points should fall on or very near the line. If
they are all off, either above or below the line, this
may suggest:
The span point is incorrectly set. Recheck the air
flow and calculations used for spans.
The zero point is incorrectly set.
The linearization circuitry of the FPD analyzer is
in need of adjustment. Refer to operation manual or to
manufacturer for aid. All possible error sources should
be investigated before adjustments are made to the
linearization circuitry. Unless you are thoroughly
familiar with this circuitry, it is best to consult the
manufacturer for advice.
13. Determine the calibration equation. Determine, or have determined
by someone, the equation for the least squares line of best fit
for all the calibration points, including zero and span.
Many hand-held calculators now have the capacity to
compute the least squares linear regression equation.
The equation will be of the form y = mx + b where:
y = analyzer response (V),
m = slope of calibration line (V per ppm),
x = concentration of S02 (ppm), and
b = intercept of the calibration line with the y-axis (V).
Using this equation, calculate the location of any two points on
the line (one point near zero, one point near full scale). Con-
nect these points with a light line and extend the line through
the y-axis as well as beyond the span point. This line should
pass through or very near to the intermediate calibration points,
the span point, and the zero point. Refer to Figure 4.3.
Ill
-------
Apply the equation to convert voltage signals stored on a
data acquisition system to concentration units. Forward the
calibration record and the least squares regression equation (if
computed) to your supervisor or to the data processing department.
This equation will be used to treat the signals stored in a DAS
until the time of the next calibration.
The equation may also be used to solve for ppm S02 concentrations
corresponding to voltage values taken manually from the stripchart.
If the calibration points lie on or very close to the calibration
curve, the S02 values may be read directly from the stripchart.
Example calculations:
x-axis y-axis
S02, ppm, from Linear response, volts
permeation tube (0-1 V output; analyzer
calibration range 0-0.5 ppm)
0.0 zero air +0.0136 (set with zero pot)
0.437 span gas 0.875 (set with span pot)
0.338 0.686
0.278 0.555
0.144 0.292
0.099 0.198
0.078 0.155
Least squares linear regression equation is:
voltage = 1.9921 [S02] + 0.0054
or, rearranging:
[S02]ppm .
Thus, for example, if a known concentration of S02 of 0.500 ppm is sampled
by the analyzer, the expected response is:
voltage = 1.9921 (0.500 ppm) + 0.0054
voltage = 1.001
As another example, if a voltage value of 0.300 is obtained, the equation
says that the concentration of S02 is:
112
-------
- 0.300 - 0.0054 _ nyio
- ~ = 0.148 ppm
ppm 1.9921
14. Return the analyzer sampling line to the station sampling mani-
fold and ambient air. Make note of this action and the time in
the notebook.
4.6 SUPPLEMENTARY INSTRUCTIONS FOR PARTICULAR FPD ANALYZERS
4.6.1 Bendix Model 8300: Electronic Zero and Operational Zero
The Bendix Model 8300 FPD S02 analyzers have two adjustable zero pots
which serve different purposes. One is located on the front panel; it is an
electronic zero and is adjusted only when the flame of the FPD is extinguished.
The second zero, located inside the cabinet, is often called the nonsulfur
suppression adjustment, and is adjusted only when the flame is burning and
zero air is being sampled. If your instrument is a new model (not Model
8300) the following instructions do not apply. For instance, the Model 8303
would not use these instructions.
4.6.1.1 Front panel electronic zero adjustment
Adjustment of the front panel electronic zero must be made while the
flame is extinguished. The following steps are taken from the Bendix oper-
ation manual.
1. Extinguish the flame by pulling the PULL TO TEST hydrogen diverter
valve fully out. Be cautious when venting hydrogen. A tube
should be attached to the vent to carry the hydrogen to the out-
side air.
2. When the flame is out, if a positive output is indicated by the
voltmeter or recorder, adjust the ZERO adjustment pot on the front
panel of the analyzer for a zero indication on the voltmeter or
recorder. This adjustment corrects for the offset of the ampli-
fiers in the Exponential Amplifier Card.
NOTE: Usually the ten-turn ZERO adjustment pot
indicator dial is factory-set at midscale; -500,
and will give a 0.001 V output when the 0-1 V range
output (located on the rear panel) is connected to
113
-------
Apply the equation to convert voltage signals stored on a
data acquisition system to concentration units. Forward the
calibration record and the least squares regression equation (if
computed) to your supervisor or to the data processing department.
This equation will be used to treat the signals stored in a DAS
until the time of the next calibration.
The equation may also be used to solve for ppm S02 concentrations
corresponding to voltage values taken manually from the stripchart.
If the calibration points lie on or very close to the calibration
curve, the S02 values may be read directly from the stripchart.
Example calculations:
x-axis y-axis
S02, ppm, from Linear response, volts
permeation tube (0-1 V output; analyzer
calibration range 0-0.5 ppm)
0.0 zero air +0.0136 (set with zero pot)
0.437 span gas 0.875 (set with span pot)
0.338 0.686
0.278 0.555
0.144 0.292
0.099 0.198
0.078 0.155
Least squares linear regression equation is:
voltage = 1.9921 [S02] + 0.0054
or, rearranging:
L"s°2]™m - voltage - 0.0054
Ppm " 1.9921
Thus, for example, if a known concentration of S02 of 0.500 ppm is sampled
by the analyzer, the expected response is:
voltage = 1.9921 (0.500 ppm) + 0.0054
voltage = 1.001
As another example, if a voltage value of 0,300 is obtained, the equation
says that the concentration of S02 is:
112
-------
- 0-300 - 0-0054 _ . ,.0
J — = 0.148 ppm
ppm 1.9921
14. Return the analyzer sampling line to the station sampling mani-
fold and ambient air. Make note of this action and the time in
the notebook.
4.6 SUPPLEMENTARY INSTRUCTIONS FOR PARTICULAR FPD ANALYZERS
4-6.1 Bendix Model 8300: Electronic Zero and Operational Zero
The Bendix Model 8300 FPD S02 analyzers have two adjustable zero pots
which serve different purposes. One is located on the front panel; it is an
electronic zero and is adjusted only when the flame of the FPD is extinguished.
The second zero, located inside the cabinet, is often called the nonsulfur
suppression adjustment, and is adjusted only when the flame is burning and
zero air is being sampled. If your instrument is a new model (not Model
8300) the following instructions do not apply. For instance, the Model 8303
would not use these instructions.
4.6.1.1 Front panel electronic zero adjustment
Adjustment of the front panel electronic zero must be made while the
flame is extinguished. The following steps are taken from the Bendix oper-
ation manual.
1. Extinguish the flame by pulling the PULL TO TEST hydrogen diverter
valve fully out. Be cautious when venting hydrogen. A tube
should be attached to the vent to carry the hydrogen to the out-
side air.
2. When the flame is out, if a positive output is indicated by the
voltmeter or recorder, adjust the ZERO adjustment pot on the front
panel of the analyzer for a zero indication on the voltmeter or
recorder. This adjustment corrects for the offset of the ampli-
fiers in the Exponential Amplifier Card.
NOTE: Usually the ten-turn ZERO adjustment pot
indicator dial is factory-set at midscale; -500,
and will give a 0.001 V output when the 0-1 V range
output (located on the rear panel) is connected to
113
-------
1.
2.
a digital voltmeter. If the voltmeter or recorder
indicates that adjustment is necessary, the ZERO
pot should require adjustment by only a few divi-
sions.
3. If a 5 percent offset of full scale and zero of the analyzer is
desired, use the front panel ZERO adjustment pot at this time.
For example, if the analyzer is in the 0-1 ppm range and has a 0-1
voltage output, the pot should be adjusted until the voltmeter or
recorder indicates 0.050 V (50 mV). This gives a "live zero."
See comments in Section 4.6.3 describing the effects of this zero
offset on the data.
4. After electronic zero adjustment is complete, return the hydrogen
diverter valve to the "in" position and relight the flame.
4.6.1.2 Internal operational zero (Nonsulfur Suppression) adjustment
The instrument should be on, the flame should be lighted, and the
instrument should be sampling zero air.
Carefully remove the top cover of the analyzer and adjust the
NONSULFUR SUPPRESSION pot (located on an interior panel of the
instrument) until a zero voltage is indicated on the voltmeter or
recorder. This adjustment is very critical. Extreme misadjust-
ment can cause a negative voltage readout. Misadjustment also
tends to cause nonlinear response, especially at low levels.
WARNING. The NONSULFUR SUPPRESSION pot is the
biasing pot for the photomultiplier tube log ampli-
fier. If it is turned too far negative, it will
bias the amplifier in an OFF position and a certain
concentration of S02 will be required to turn the
amplifier on. This, in effect, causes loss of
detection of low-level sulfur concentrations.
If the pot adjustment is too positive it will cause
the amplifier to come on and show a positive re-
sponse in the absence of of S02. In this condi-
tion, nonlinear behavior is also observed.
3. Operate the instrument on,zero air for 30 minutes to be sure there
is no zero drift.
114
-------
4. Return to the calibration procedure, Section 4.5 of this document,
and continue with the span adjustment.
4-6.2 Use of the Optional Log-Li near Output of Meloy FPD Analyzers
There are several signal outputs available from various models of the
Meloy (or the earlier Melpar) FPD S02 analyzer. These are the log-log
output (plotted as log of amperage versus log of concentration), and the
linearized output (plotted as linear voltage versus linear concentration).
The linearized output is most commonly used and most instruments are
purchased with the optional linearization circuit included. Linearizing
circuitry "packages" are also available. A discussion of the log-log and
log-linear outputs is given below.
4.6.2.1 Log-log output
The output signal from the photomultiplier tube is in the form of an
electrical current. This signal is an exponential function which plots
linearly versus concentration on log-log paper with a slope of 1.4 to 2.0,
depending on the burner characteristics. Figure 4.4 shows a log-log plot of
S02 concentration, ppm, versus the photomultiplier current output of a
typical Meloy FPD S02 analyzer.
The log-log output is not commonly available on Meloy ambient air
analyzers. The output more commonly available at the rear panel is the
log-linear output discussed below.
4.6.2.2 Log-linear output
Meloy Laboratories employs a patented amplifier which converts the
current from the PM tube to a voltage. This amplifier also has a log re-
sponse which is adjustable so that a 0-1 V output may represent up to six
decades of input current. By using this log/linear amplifier, a wide dy-
namic range is obtained with excellent readability for low S02 concentra-
tions.
Figure 4.5 is a plot of typical calibration data, and shows S02 concen-
tration, ppm, versus the voltage output from the log/linear amplifier. In
this particular instrument, a voltage output of 0.000 V corresponds to 0.000
ppm S02 and 1.000 V to 0.500 ppm S02. Note that the output is plotted on
semi log graph. The S02 concentration is plotted on the logarithmic x-axis,
the analysis response, volts, is entered using the linear y-axis.
115
-------
LOG-LOG OUTPUT
1 0.08 ppm
0 10 20 30 40 50 60 70 80 90 100
TYPICAL ANALYZER
CALIBRATION CURVE
CHART RECORDED READINGS
Figure 4.4. Log-log output of the Meloy Model SA 185
FPD S02 analyzer.
116
-------
1.0
0.9
0.8
c/»
5 0.7
o
>
!5 0.6
Q.
"
0.3
cd 0.2
0.1
ta
o
1.0
0.1
Concentration, ppm
0.01
Figure 4.5. Log-linear plot of calibration data, Meloy model SA 185-2A FPD S02 analyzer.
-------
Other concentrations of S02 may be read from the curve if the voltage
output of the calibrated analyzer is known. For example, a voltage output
of 0.460 corresponds to an S02 concentration of 0.048 ppm.
If data are recorded on linear stripchart paper, the concentration
value cannot be read directly from the chart. Instead the voltage value (or
alternatively, the number of chart divisions) is read from the stripchart
and the ppm (or ug/m3) value taken from the calibration curve (e.g., Figure
4.5). Logarithmic stripchart paper may also be used. Concentration values
are then read directly from the chart.
If log/linear voltage data are stored on magnetic tape by a data acqui-
sition system, an equation must be employed to convert the raw voltage
signal to physical units. Such an equation is developed in Section 4.6.3 of
this document.
4.6.3 Data Correction Due to Baseline Offset of the Meloy Lab's Model
SA 185 Output
Some users may prefer to offset the "zero" baseline output of Meloy
Model SA 185 FPD sulfur analyzers to some point higher on the output voltage
scale to allow observation of any negative drift which might occur. Indeed,
in the early models, which use electronic rather than thermal flame-off
detection, such negative drift can cause hydrogen shutoff with subsequent
unnecessary downtime.
When offset is used, the data of the normalized logarithmic output are
no longer applicable and an error, the magnitude of which depends on the
amount of offset, is introduced into the data being collected.
The maximum error occurs at the lower levels of concentration due to
the nature of the logarithmic curve. The mathematical expression used to
calculate the effect is given below. Correction tables, calculated from
that expression, for offset voltages of +0.065 V (0.01 ppm) and +0.147 V
(0.015 ppm) for a typical SA 185 calibration curve are also provided. In
the data shown with a 0.01 ppm offset the precision error is no greater than
+0.003 ppm and is reduced, in the area of 0.04 ppm, to insignificance (+0.001
ppm).
Two possibilities for data correction exist. First, a gross error of
approximately 0.003 ppm can be subtracted from all readings below 0.040 ppm.
118
-------
Second, an exact correction based on an equation and the calibration curve
supplied with your unit(s) can be used either manually or with a computer,
if that type of data treatment is desired. A computer can be programmed
easily to correct each data point or to provide a correction table.
There is a third possibility. It is to accept the readings without
correction, knowing that a possible error of +0.004 ppm at very low concen-
trations exists but is not significant enough to cause concern.
The equation used to determine actual concentration versus output
signal when the baseline (zero gas value) is offset (that is, the output
zero value is greater than zero) is:
[S02] = 0.007260 [eVRA - eV0A]B
where:
[S0?] = actual concentration, ppm
e = natural logarithm base = 2.71828
Vp = output signal voltage with sample divided by output voltage
at 1 ppm (Full Scale)
Vn = output voltage with zero gas introduced to analyzer divided
by output voltage at 1 ppm (Full Scale)
A = 1.0695 [In (A-j/Ag)]
- (4.6052)
B [In (A^/Ag)]
A = current output in amps from calibration curve at 1 ppm S02
A = current output in amps from calibration curve at 0.010 ppm S02
In = natural log of value in parenthesis
An example of the equation use and the resulting error using a typical
calibration curve is:
A = 4.55 x 10"9 amps at 0.01 pptn S02
and _c __
A = 3.85 x 10 amps at 1.0 ppm SU2
119
-------
therefore:
A = 9.0433
A = 1.0695 (9.0433) = 9.672
_ (4.6052) _ Q 5Q92
8 ' (9.0433) ~ °-5092
with a baseline offset of 0.065 V (0.01 ppm on the meter):
eV = e(0-065) (0'672) = 1.875
using this "typical calibration curve" data for Table 4.2 were prepared. As
can be seen from Table 4.2, the error is only 0.003 ppm when the meter or
output reads 0.020. The error quickly decreases so that at a reading of
0.05 ppm or greater there is essentially no error due to the offset (a
%0.001 ppm variation is attributed to mathematical error due to rounding
off).
Table 4.3 shows the effect of a 0.015 ppm offset. The error, although
greater at very low concentrations, becomes insignificant at 0.07 ppm concen-
tration level.
Table 4.2. Typical effect of an offset of 0.065 V (0.01 ppm)
VR
0.065
0.206
0.288
0.346
0.392
0.533
0.673
0.756
0.859
0.928
1.000
Meter Reading
S02 (ppm)
0.01
0.02
0.03
0.04
0.05
0.10
0.20
0.30
0.50
0.70
1.00
Actual
Concentration (ppm)
0.000
0.017
0.028
0.039
0.049
0.100
0.199
0.300
0.499
0.701
1.000
Error
(ppm)
Not Applicable
+0.003
+0.002
+0.001
+0.001
0
+0.001
0
+0.001
-0.001
0
120
-------
Table 4.3. Typical effect of an offset of 0.147 V (0.015 ppm)
v Meter Reading
R S02 (ppm)
0.147
0.206
0.288
0.346
0.392
0.533
0.673
0.756
0.859
0.928
1.000
0.015
0.020
0.030
0.040
0.050
0.100
0.200
0.300
0.500
0.700
1.000
Actual
(ppm)
0.000
0.013
0.026
0.037
0.048
0.100
0.199
0.300
0.499
0.701
0.999
Error
(ppm)
Not Applicable
+0. 007
+0.004
+0.003
+0.002
0
+0.001
0
+0.001
-0.001
+0.001
4.7 SUMMARY OF FPD ANALYZER PARAMETERS WHICH MUST BE OPERATOR-CONTROLLED
Operator-controlled parameters relating to the operation of an ambient
air S02 FPD analyzer are summarized in Table 4.4. The table lists the
parameter, how the operator controls the parameter, how the operator may
identify lack of control of the parameter, and how the operator may bring
the parameter into control.
121
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Table 4.4 FPD analyzer parameters which must be operator-controlled
in order to obtain valid data
PARAMETER
Air sample flow rate, cc/minute
How Operator Controls Parameter
Needle Valve. (NOTE: Monitor Labs Model 8450 and Meloy Model 285 have a preset control which
operator cannot adjust.)
How Operator May Identify Lack of Control
1. Test airflow to sample inlet with calibrated bubble flowmeter or calibrated mass flowmeter.
After correction to 760 mm Hg, 25°C, compare to previous determination and/or manufacturer's
setting.
2. Check the instrument's calibrated air rotameter and compare setting with that found at last
calibration. (NOTE: Most air rotameters measure zero air from internal source and not
the actual sample flow; therefore, use flowmeter check in addition to rotameter check.) After
long periods of use, rotameters may exhibit "sag." The rotameter ball will move to a new
location, but the same flow rate will continue. This is caused by a combination of electro-
static effects and scratching of the rotameter column by the rotameter float.
How Operator May Bring Parameter Into Control
1. Remove any obstructions to flow. (Dirty Teflon filter, dirty, kinked, or bent Teflon tubing,
dirt-plugged orifice, defective Teflon solenoid valve, plugged or bent exhaust line,
plugged dilution air inlet orifice and/or filter, Teflon tubing squeezed shut by compression
fitting, etc.)
2. Eliminate any leaks in sample flow system. (Ill-fitting particulate filter, loose compression
fitting, loose or poor connection of sampling line to sampling manifold, leaking solenoid
valve, loose connection to sampling pump, etc.)
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
How Operator May Bring Parameter Into Control (continued)
3. Verify sample pump performance. (Sample pumps periodically need new diaphragms or valve
assemblies. Dust particles can affect the flow and the flow will vary with length of
pump operation.)
4. Check burner assembly components for water vapor condensation and corrosion. (Verify
heater operation and clean or replace corroded components.)
ro
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Hydrogen flow rate, cc/minute
How Operator Controls Parameter
Hydrogen pressure regulator and gauge. (Some older analyzers have a needle valve control or a
pressure regulator with no gauge. These adjustments are in addition to the pressure regulator
and gauge located at the hydrogen tank or generator.)
How Operator May Identify Lack of Control
1. Check the instrument's calibrated H2 rotameter and compare setting with that found at last
calibration, and/or with manufacturer's suggested setting. Be certain the rotameter is
not "sticking."
2. Disconnect hydrogen feed at burner assembly, override the hydrogen shutoff control, and
measure flow with bubble flowmeter or calibrated hydrogen mass flowmeter. (Caution! Hydrogen
is a flammable gas; provide adequate ventilation.) Compare with previously determined H2
flow rates.
How Operator May Bring Parameter Into Control
1. Check hydrogen source (cylinder or generator) for adequate pressure and pressure setting.
2. Be certain H2 solenoid is not sticking shut.
3. Check for obstructions to flow (bent metal tubing). Check for leaks with leak detector
solution.
4. Check burner assembly for corrosion.
-------
en
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Interferences to S0g Detectability
1. Sulfur compounds other than S02
2. Carbon dioxide
3. Water condensation
4. Stainless steel or plastic tubing in sampling line
5. S02 removed in the presence of 03 in heated H2S silver scrubber
How Operator Controls Parameter
1. The positive interference of sulfur compounds other than S02 is eliminated by use of a scrubber
which is available from the instrument manufacturer. Determine or estimate the average con-
centration of H2S for the area in ppm. Use the manufacturer's ppm-hours rating of scrubber
to compute expected lifetime for the area.
2. The negative interference of carbon dioxide is minimized by calibration with air containing
ambient levels of C02. (Refer to discussion of clean air supplies for FPD calibration,
Section 3.3.)
3. The negative effect of water condensation in manifold and sampling lines is minimized
by proper temperature and humidity control of the room housing the analyzer.
4. Stainless steel, rubber, polyethylene, etc., tubing is never used as a sample line
since S02 absorbs and reacts. Use only Teflon.
5. Keep H2S scrubber temperature as low as possible to obtain optimum performance. Instruments
equipped with unheated scrubbers show less interference.
How Operator May Identify Lack of Control
1. Challenge the scrubber with a low level of H2S and check for analyzer response. If response
occurs, scrubber is not effective.
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
ro
How Operator May Identify Lack of Control (continued)
2. Perform independent calibration check (make no adjustments) of analyzer with calibration system
known to have =350 ppm C02 present. Compare calibration curves and see if the analyzer's
response has diminished. (Refer to Section 3.0, Effects of C02.)
3. S02 concentration at time of pre-calibration check is lower than expected. Visible moisture
present in sample line or station manifold.
4. Inspect analyzer and sampling lines for proper material (Teflon).
5. Challenge analyzer with S02, then with S02 plus 03.
How Operator May Bring Parameter Into Control
1. Replace or clean the scrubber according to manufacturer's instructions.
2. Perform calibration with ambient level of C02 present in the calibration gas. (See Section 5.0
for a procedure for determination of ambient levels of C02.)
3. Maintain high enough room temperature such that H20 condensation does not occur.
4. Replace steel or plastic tubing with Teflon tubing.
5. Use unheated H2S scrubber. Check temperature control of heated scrubber.
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Temperatures
1. Shelter temperature
2. Temperature of analyzer components (photomultiplier tube housing, burner block, and exhaust
assembly, H2S scrubber)
How Operator Controls Parameter
1. Adjust heating/air conditioning controls or shelter.
2. Operator cannot control temperatures of analyzer components.
How Operator May Identify Lack of Control
1. Shelter temperature is outside the limits of 20-30°C (68-86°F).
2. The following may indicate lack of instrument temperature control.
a. Zero or span signal is unsteady. Photomultiplier tube housing temperature may be
varying. This affects the PMT output and H2 flow controlling capillaries or
other pneumatic impedance elements. Check for proper temperature by use of built-in
thermocouple or status light of analyzer.
b. Flame will not light, or moisture droplets appear in exhaust line. This may indicate
that the burner block and exhaust manifold have lost heat and allowed condensation to
occur. Check thermocouple or status light. Touch burner block and exhaust lines
cautiously. They should be very hot.
c. H2S scrubber fails to scrub H2S. This could indicate failure of heater element in
scrubber.
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued
ro
oo
How Operator May Bring Parameter Into Control
1. Adjust shelter temperature.
2. Replace defective heaters.
-------
Table 4.4. FPD analyzer parameters which must be operator-controlled
in order to obtain valid data (continued)
PARAMETER
Linearity of signal output
How Operator Controls Parameter
Adjustments of Linearization Electronic Circuitry. CAUTION! Do not adjust without first
determining this is truly the problem. (NOTE: the linearization circuitry is factory-set for
the Monitor Labs Model 8450 and cannot be operator-adjusted.)
How Operator May Identify Lack of Control
Operator performs multipoint calibration and examines graphical plot of analyzer response for
departures from linearity. (Refer to Calibration Section 4.0 and Linearization Procedures, in
the manufacturer's instruction manual.)
How Operator May Bring Parameter Into Control
Operator generates S02 calibration gases (zero, span, and intermediate points) and adjusts
linearization circuitry until linearity is achieved. (See Linearization Procedures in the
manufacturer's instruction manual.) The use of a picoamp source to generate amperage signals
equal to those expected from S02 is another approach to establishing linearity (consult
manufacturer).
Concluded
-------
130
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SECTION 5.0
PROCEDURAL AIDS
5.1 INTRODUCTION
Establishing and maintaining sample and calibration gas flow rates is
essential to obtaining quality data from any ambient air analyzer. Proce-
dures, explanations, and precautions for determining and correcting air-
flows are given in this section.
A common piece of equipment for determining the volumetric flow of a
gas is the soap film flowmeter or bubble flowmeter (Section 5.2). Such
flowmeters can be bought commercially or built in glassblowing shops. All
soap film flowmeters should be calibrated by water displacement or by compar-
ison to a certified soap film whose volume is traceable to NBS standards of
volume. An example of a certified soap film flowmeter is the Hastings Model
HBM-1 which is available from the Hastings Raydist Company, Hampton, Virginia.
Section 5.3 discusses the use and care of the mercury barometer which
is used to determine atmospheric pressure. Section 5.4 discusses the use of
a water manometer which is used to determine very slight variations in
pressure. Section 5.5 discusses an equation to correct volumetric flow
rates to the normal conditions of 25° C and 760 mm Hg.
Section 5.6 outlines a quantitative method for determining the C02
content of ambient air or air from clean air supplies.
131
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5.2 SOAP FILM FLOWMETER, SFFM, OR BUBBLE FLOWMETER
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
1. Choose the size SFFM
needed for the job.
Be certain it is cali-
brated or certified.19
See Figure 5.1
2. Place SFFM on level
spot and secure it
to prevent tipping.
3. Fill reservoir
with soap solution.
4. Connect SFFM to gas
tubTng of flowing
system.
a. If source pushes
gas out, connect
to lower port of
SFFM (upper port
open).
b. If source pull
gas in, connect
to upper port of
SFFM (lower port
open).
c. If measuring an
inline flow, break
into system and
connect both
ports, making
closed loop.
If flowmeter volume is
too smal1, one cannot
accurately time the
soap film movement.
About 30-60 seconds
time for measurements
is desirable.
Inaccurate readings
may be obtained if
SFFM is not level. A
ringstand with soft
clamps is a convenient
holder.
A liquid leak detector,
such as "SNOOP®" is sug-
gested.
Leak-free connection
is essential. Use one
of the following:
a. Ground glass ball/
socket fittings
and clamp.
b. Compression fit-
tings with soft
rubber or Teflon
gaskets.
c. Smaller tubing
forced tightly in-
to or over larger
tubing.
If gas flow rate
is less that 2 cc/
minute, gas dif-
fusion through
soap film is
appreciable. Do
not use SFFM for
very low flow
measurements.
Do not over-
tighten clamps.
Fill reservoir and
lines to a point
just below lower
air inlet to
SFFM.
Double check the
direction of air
flow. If soap
solution is
pulled .into an
instrument it
may be ruined.
Use of an inline
liquid trap is
suggested.
Be cautious
when measuring
toxic or flammable
gases. Provide
ventilation to
the outside via
6.3 mm (1/4 in.)
tubing. Work in
a fume hood.
132
-------
UPPER PORT
'BUBBLE BREAKER
TOP GRADUATION LINE
INTERMEDIATE
GRADUATION LINE
LOWER GRADUATION LINE >•
lOOcc
50 cc
Occ
BASE
LOWER PORT
RUBBER BULB
Figure 5.1. Soap film flowmeter.
133
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5.2 SOAP FILM FLOWMETER, SFFM, OR BUBBLE FLOWMETER (con.)
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
Lift soap solution
reservoir tube or
depress rubber
bulb-to create
soap film bubble.
Release 10 to
20 bubbles to wet
interior surface.
Measure the flow
rate of gas
through the
SFFM.
Take three
separate meas-
urements.
As the liquid rises
above the lower port
of SFFM, air entering
this port will create
a bubble and carry
the film upward. At
this point, release
tube or bulb.
Allow all bubbles
to clear the SFFM
column. With stop-
watch in hand, start
a single uniform
soap film up the
column.
Observe the lower
graduation line of
the SFFM at eye level
and as the film passes
this mark, start the
watch.
Use suffi-
ciently large
inlet lines to
avoid back-
pressure and
flow change.
Do not pres-
surize the SFFM
by attaching an
exhaust line
that is too small
in diameter and/
or too long in
length.
When measuring
inline, keep con-
nections as short
as possible.
Do not allow the
bubbles to be
carried into
the instrument.
Use a "bubble
breaker" atop the
SFFM to break
the film surface.
Be sure, to
observe soap
film travel
by sighting
along the plane
of the film.
Do not touch
the rubber bulb
during a reading.
134
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5.2 SOAP FILM FLOWMETER, SFFM, OR BUBBLE FLOWMETER (con.)
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
7. Compute the volu-
metric flow rate.
Average the three
values to obtain
final value.
Record all data
calculations in note-
book.
Stop the watch
when the soap film
crosses the top
graduation or some
known intermediate
graduation.
Divide the volume of
the flowmeter (or the
volume traversed), cc,
by the time required,
minutes.
Example calculation:
Soap film traverses
100 cc in 39 seconds.
39 sec = 0.65 min
60 sec/min
If necessary for
comparison, this
volumetric flow
rate should be
corrected to
standard temper-
ature (25° C)
and pressure
(760 mm Hg).
Also correct
for water
vapor pressure.
See Section 5.5.
8. Disconnect SFFM
from and gas
source.
C(
n
0.65 mm
=153.8 cc/min
is the uncorrected
volume flow rate.
Be certain that
all disconnected
fittings, etc.
are retightened
and leak-tested.
135
-------
5.3 MERCURY COLUMN BAROMETER, FORTIN TYPE
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
1.
2.
3.
Assure that the baro-
meter is mounted pro-
perly, and that the
mercury is clean.
Adjust mercury reser-
voir leveling screw so
liquid mercury just
touches sharp point
of ivory zero point.
Locate the top of
the mercury column,
then tap the baro-
meter case lightly
with fingers.
Adjust vernier
plate with notched
wheel until lower
edge of vernier
is in same plane
as top of mer-
cury meniscus.
Barometer should be
wall-mounted vertical-
ly and be perpendicular
to a level floor.
Dirty mercury is dull,
tarnished.
This adjusts the
level of mercury in
the cistern to the
same point for each
reading. A flash-
light provides
helpful illumination.
Adjust until the zero
pointer makes a slight
"dimple" in the mer-
cury pool, then "back-
off" slightly.
The height of the mer-
cury meniscus (the
curvature of the mer-
cury surface inside a
glass tube) is greater
on a rising barometer
than a falling one.
Tapping brings the
meniscus to an average
height.
This process locates
the top of the mercury
column.
If barometer is
not level or
mercury is dirty,
erroneous read-
ings are obtained.
Return to
factory if mer-
cury column
contains dirty
mercury.
Do not force
or strain the
adjusting screw. .
When reading
barometer, the
reader's eye
should be in
the same hori-
zontal plane
as the top of
the meniscus
and the lower
edge of the
136
-------
5.3 MERCURY COLUMN BAROMETER, FORTIN TYPE (con.
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
5.
Determine reading in
English or metric
units.
a. Read column
height.
b. Read fractional
value from venier
scale.
6.
Apply corrections for
the temperature of the
barometer, and if
desired, gravity.
To read column height,
determine scale value
that lower line of
venier intercepts or
is just above.
Read venier by deter-
mining which one of
the 9 division marks
(1 to 9) intersects
most closely with
scale value lines.
Example:
Lower line of ver-
nier "crosses" between
755 and 756 mm Hg.
This says the read-
ing is between 755 and
756 mm Hg.
The vernier line
marked "8" matches ex-
actly with the 771 mm
line of the scale.
Thus, the uncorrect-
ed barometric pressure
is 755.8 mm Hg.
Temperature affects
the expansion of mer-
cury and the scale
metal.
vernier plate.
Line your sight
on the bottom
of vernier and
the metal ver-
nier guide lo-
cated behind
the mercury
column.
If it is desired
convert an English
reading to a metric
reading or vice
137
-------
5.3 MERCURY COLUMN BAROMETER, FORTIN TYPE (con.)
PROCEDURE RESULTS, EXPLANATION PRECAUTION
Temperature correc- versa, always
tion tables and in- apply the tempera-
Use the corrected instructions for their ture and gravity
pressure reading use for English and corrections before
to calculate gas metric scales accom- making the con-
volumes at stan- pany the barometer or version.
dard temperatures may be found in such
and pressure. publications as the
Handbook of Chemistry
and Physics.
Take the tempera-
ture reading from the
thermometer attached
to the barometer or
from a therometer
in the same area.
138
-------
5.4 WATER MANOMETER, U-TUBE
PROCEDURE
RESULTS, EXPLANATION
PRECAUTION
1.
Choose a U-Tube water
or oil manometer.
See Figure 5.2
4.
Level the manometer
so liquid levels in
both sides of the
"U" are the same.
Attach, by use of
rubber tubing, one
side of the "U" to
the manifold or
other item for which
the pressure differ-
ential is desired.
Read the manometer
establish AP, inches
of H20 or cm of H20.
As the moving gas
stream sweeps by, a
slight vacuum may be
created.
If the manifold is
pressurized, a positive
pressure will be shown.
Read the difference in
heights of the water
level in the two sides
of the "U". See
Figure 5.2
Manometers using
liquids other
than water (such
as red oi1) wi11
have graduations
different from
H20 manometers.
Be sure to use
the correct fluid.
Leave the other
side of the "U"
open to the at-
mosphere.
If greater than
1 to 2 inches
H20 pressure is
noted, the FPD
zero stability
may be affected.
Rework any cali-
bration manifolds
which display
such character-
istics.
139
-------
TUBE CONNECTED TO PORT OF MANIFOLD, ETC.
-IS.
O
THIS END OPEN
ATMOSPHERE
\\\\\\\\\
i
J
t
AP
i
I— -r- P
P2
k /
1
AP = 0
ATMOSPHERIC PRESSURE
AP= 1.5 INCHES H20
SLIGHT VACUUM ON MANIFOLD
AP = 1.5 INCHES H20
SLIGHT POSITIVE PRESSURE
IN MANIFOLD, EXCEEDING
ATMOSPHERIC PRESSURE
Figure 5.2. Water manometer, "U" tube.
-------
5.5 STEPS FOR CORRECTING AIRFLOW TO STANDARD TEMPERATURE AND PRESSURE
In air pollution work, the standard temperature is 25° C; the standard
pressure is 1 atmosphere or 760 mm Hg (29.92 inches Hg). Almost all flow
measurements taken by volumetric displacement methods must be corrected to
standard temperature and pressure for comparisons to other work. Soap film
flowmeter and wet test meter measurements must also be corrected for the
effect of water vapor. Table 5.1 lists the vapor pressure of water (mm Hg)
at various temperatures.
Apply this equation to correct flows:
F = F x P " P' x 298'15
s 760 x t + 273.15
where:
F = flow rate at standard conditions in liters/minute
j
F = measured flow rate in liters/minute by displacement
P = barometric pressure in mm Hg
P' = vapor pressure of water, mm Hg, at temperature t.
t = air temperature, degrees C
For an example calculation using this equation, refer to Section 3.4.4.
5.6 ASCARITE® METHOD FOR C02 DETERMINATION
Average levels of C02 in ambient air or in air from clean air sources
can be determined gravimetrically by adsorption and reaction of C02 on
Ascarite. The increase in the weight of the tube containing the Ascarite
can be related to the C02 concentration.
This method is based on the instructions given in the APHA manual,
Methods of Air Sampling and Analysis, "Tentative Method for Preparation of
Carbon Monoxide Standard Mixtures," p. 224, 1972.
Ascarite is available from most laboratory supply houses. A mesh of
8-20 is specified for this procedure. As Ascarite collects C02, its color
changes from brown to white due to sodium carbonate formation.
141
-------
Table 5.1. Vapor pressure of water at
various temperatures, mm Hg
Temp.
°C
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
0.0
17.535
18.650
19.827
21.068
22.377
23.756
25.209
26.739
28.349
30.043
31.824
33.695
35.663
37.729
39.898
42.175
44.563
47.067
49.692
52.442
55.324
58.34
61.50
64.80
68.26
71.88
75.65
79.60
83.71
88.02
92.51
97.20
102.09
107.20
112.51
118.04
123.80
129.82
136.08
142.60
0.2
17.753
18.880
20.070
21.324
22.648
24.039
25.509
27.055
28.680
30.392
32.191
34.082
36.068
38.155
40.344
42.644
45.054
47.582
50.231
53.009
55.91
58.96
62.14
65.48
68.97
72.62
76.43
80.41
84.56
88.90
93.5
98.2
103.1
108.2
113.6
119.1
125.0
131.0
137.3
143.9
0.4
17.974
19.113
20.316
21.583
22.922
24.326
25.812
27.374
29.015
30.745
32.561
34.471
36.477
38.584
40.796
43.117
45.549
48.102
50.774
53.580
56.51
59.58
62.80
66.16
69.69
73.36
77.21
81.23
85.42
89.79
94.4
99.1
104.1
109.3
114.7
120.3
126.2
132.3
138.5
145.2
0.6
18.197
19.349
20.565
21.845
23.198
24.617
26.117
27.696
29.354
31.102
32.934
34.864
36.891
39.018
41.251
43.595
46.050
48.627
51.323
54.156
57.11
60.22
63.46
66.86
70.41
74.12
78.00
82.05
86.28
90.69
95.3
100.1
105.1
110.4
115.8
121.5
127.4
133.5
139.9
146.6
0.8
18.422
19.587
20.815
22.110
23.476
24.912
26.426
28.021
29.697
31.461
33.312
35.261
37.308
39.457
41.710
44.078
46.556
49.157
51.879
54.737
57.72
60.86
64.12
67.56
71.14
74.88
78.80
82.87
87.14
91.59
96.3
101.1
106.2
111.4
116.9
122.6
128.6
134.7
141.2
148.0
Source: Handbook of Chemistry and Physics, 50th Ed. The Chemical Rubber Co.,
Cleveland, Ohio.
142
-------
5.6.1 Procedure
Loosely pack the Ascarite into 15 to 20 cm length (6 to 8 in.) glass or
plastic tubes having a 1.27 cm (0.5 in) inside diameter. Plug the ends with
glass wool and cap to protect from moisture. Carefully weigh the tube on an
analytical balance to the nearest milligram. Do the same with a tube contain-
ing Drierite.
Set up a sampling train similar to the one shown in Figure 5.3.
Determine the flow rate into the Ascarite cartridge. 500-1000 cc/min
is a reasonable flow.
Collect air for a sufficient length of time to obtain an accurate
weight difference; about 30-60 minutes. Express the total flow volume in
cubic meters at STP; express the weight gain in micrograms. Compute the ppm
value of C02.
Example calculation:
Air flow rate = 500 cc/min at STP (25° C, 760 mm Hg)
Time = 30 minutes
Total weight gain = 0.0094 grams (9400 ug)
(total weight gain = Ascarite tube gain + Drierite tube gain)
Thus:
0.5 liters/min x 30 min = 15 liters = 0.015 m3
9400 ug _ X ug
0.015 m3 1 ms
X = 626667 ug
Therefore, since 1798 ug/m3 C02 = 1 ppm C02 at STP
C02, ppm = 626667 = M8 ppm
1798
In field use, this Ascarite C02 collection system has been shown to
have an accuracy of 5 percent or better and a precision of ±12 ppm for
22
co-located sampling systems."
143
-------
AIR SOURCE IN AT
KNOWN FLOW RATE
/
TUBE CONTAINING
DRIERITE TO REMOVE
MOISTURE FROM AIR
FLOW CONTROL VALVE
PREWEIGHED TUBE
CONTAINING ASCARITE
TO CAPTURE C02
PREWEIGHED TUBE CONTAINING
DRIERITE TO CAPTURE ANY WATER
LEAVING THE ASCARITE CARTRIDGE
METAL BELLOWS
OR DIAPHRAGM
PUMP
FLEXIBLE PLASTIC
TUBING
AIR
OUT
Figure 5.3. Ascarite sampling train for C02 determination.
-------
REFERENCES
1. R. Mavrodineanu, ed., "Analytical Flame Spectroscopy," Macmillan,
London, 1970. p. 282.
2. P. T. Gilbert, "Monitoring of Phosphorous and Sulfur by Chemilumine-
scent Flame Spectrophotometry," Proceedings of Conference of Spectro-
scopy, Instrumentation, and Chemistry, San Francisco, October 23, 1964.
3. J. A. Dean and T. C. Rains, Flame Emission and Atomic Absorption Spec-
trometry. Vol. 3, Marcel Dekker, New York, 1975, p. 33(h
4.- A. G. Gaydon and G. Whittingham, "The Spectra of Flames Containing Oxides
of Sulphur," Proc. Royal Soc. London, Series A, 189, 313 (1947).
5. A. Fowler and W. M. Yaidya, "The Spectrum of the Flame of Carbon Disulfide,"
Proc. Royal Soc. London. Series A, 132. 310 (1931).
6. A. G. Gaydon, The Spectroscopy of Flames, John Wiley and Sons, Inc.,
New York, 1957, p. 220.
7. G. W. Castellan, Physical Chemistry, Addison-Wesley Publishing Co.,
Inc., Reading, Mass., 1964. p. 565.
8. Heinrich Dragerwerk, and W. Drager, German patent 1-133918; date of
arrival, January 19, 1961; date of patent, July 26, 1962.
9. W. L. Crider, "Hydrogen Flame Emission Spectrophotometry in Monitoring
Air for Sulfur Dioxide and Sulfuric Acid Aerosol," Anal. Chem. 37, 1770
(1965).
10. S. S. Brody and J. E. Chaney, "Flame Photometric Detector: The Appli-
cation of a Specific Detector for P and for S Compounds - Sensitive to
Subnanogram Quantities," J. Gas Chromatog., 4, 42 (1966).
11. D. P. Lucero and J. W. Paljug, "Monitoring Sulfur Compounds by Flame
Photometry," Instrumentation for Monitoring Air Quality. American
Society for Testing and Materials, 1976. pp. 20-35.
12. R. E. Baumgardner, T. A. Clark, and R. K. Stevens, "Increased Specificity
in the Measurement of Sulfur Compounds with the Flame Photometric Detector,
Anal. Chem. 47, 563 (1975).
13. R. K. Stevens, A. E. O'Keeffe, and G. C. Ortman, "Absolute Calibration
of a Flame Photometric Detector to Volatile Sulfur Compounds at Sub-Part-
Per-MiTlion Levels," Environ. Science and Tech., 3, 652 (1969).
145
-------
14. D. P. Lucero, "Ultra Low-Level Calibration Gas Generation by Multistage
Dilution Techniques," Calibration jji Air Monitoring, ASTM STP 598.
American Society for Testing and Materials, 1976. pp. 301-319.
15. Daniel P. Lucero, "Performance Characteristics of Permeation Tubes,"
Anal. Chem. 43, 1744 (1971).
16. A. E. O'Keeffe and G. C. Ortman, "Primary Standards for Trace Gas
Analysis," Anal. Chem. 38, 760 (1966).
17. F. P. Scaringelli, S. A. Frey, and B. E. Saltzman, "Evaluation of
Teflon Permeation Tubes for Use with Sulfur Dioxide." Amer. Ind. Hygiene
Assoc. J. 28, 260 (1967).
18. F. P. Scaringelli, A. E. O'Keeffe, E. Rosenberg, and J. P. Bell,
"Preparation of Known Concentrations of Gases and Vapors with Permeation
Devices Calibrated Gravimetrically." Anal. Chem. 42, 871 (1970).
19. G. 0. Nelson, Controlled Test Atmospheres. Ann Arbor Science Pub-
lishers, Inc., Ann Arbor, Michigan, 1971. pp. 134-141.
20. S. G. Wechter, "Preparation of Stable Pollution Gas Standards Using
Treated Aluminum Cylinders." Calibration jji Air Monitoring, ASTM
STP 598. American Society for Testing and Materials, 1976. pp. 40-54.
21. I. Gellman, "An Investigation of H2S and S02 Calibration Cylinder Gas
Stability and Their Standardization Using Wet Chemical Techniques."
Special Report No. 76-06. National Council of the Paper Industry for
Air and Stream Improvement, Inc., August, 1976.
22. F. Smith, Research Triangle Institute, Research Triangle Park, N.C.
Unpublished results, 1976.
23. D. J. von Lehmden, "Suppression Effect of C02 on FPD Total Sulfur Air
Analyzers and Recommended Corrective Action." Proceedings, Fourth
Joint Conference on Sensing of Environmental Pollutants. New Orleans,
La., November 6-11, 1977.
24. C. E. Junge, Air Chemistry and Radioactivity. Academic Press. New
York, 1963. p. 21.
146
-------
INDEX
Air, compressed
Alumina
Aluminum cylinder
Ascarite®
Barometer
Barometric pressure
Bendix, analyzer
Burner block
cleaning
description
tip
Calibration
Calibrator
S02 cylinder
S02 tube
Carbon dioxide
quenching
Charcoal, activated
Clean air supply
Data acquisition system
Detector output
linearized
log-linear
log-log
Diatomic sulfur
Dilution air
Drying agents
Drierite
Mole sieves
Silica gel
Dynamic calibration
Electrical requirements
Electrolytic H2
Equivalent methods
Exhaust, FPD
Filters
Dilution air
Sample
Teflon
"Flame-out"
Flame photometer
analyzer
Flowrate
Air sample
Flowmeter
Hydrogen
39
38
61
38, 141
136
90,136
8,113
12
6
32
81,99
49
60
54
68
37,73
36
88
35,129
115
8
J
13,35
38,73
73
38,73
81,99
18
29
9,11
19
13
24,96
24,96
31
5
122
132
124
Hydrogen
Cylinders
Electrolytic
Flame
Fuel
Safe use
Hydrogen sulfide
Scrubber
Humidity control
Ignition, FPD
Installation, FPD
Interferences, S02
Leak tests
Hydrogen
Linearity
MACE® filter
Maintenance
Manifold
Calibration
Connections
Sampling
Manometer
Meloy, analyzer
Molecular sieves
Monitor Labs, analyzer
Multipoint calibration
NBS
Non-equivalent FPD
Oven, permeation
Oxygen/nitrogen ratio
Permeation tube
Installation
Oven
Rate
Temperature
Use
Pneumatic connections
Ambient air
Exhaust
Dilution air
H2 fuel
Portable calibrator
Pressure
Pumps
Repair
Sample
25
29
6
4,25
26
4,13
18
31
17
79, 125
77
28
129
96
95
46,64
21
20
139
8,115
73
8
81,99
40
10
45,49
72
39
55
45,49
58,76
67,77
42
24
25
13
25
53
90
12
12
Quality control
Quenching
Carbon dioxide
Self-collisional
Rack-mounting
Recorder connections
Record-keeping
Regulators, pressure
Evacuation
H2
S02
S2*
Formation
Spectra
Safety
Electrical
Hydrogen
Signal cable
Soap film flowmeter
Soda lime
Span check
Standard Reference
Material
Stripchart recorder
Sulfur dioxide
Cylinders
Permeation devices
Safe use
Temperature control
Analyzer
Station
Thermistor
Thermometer
Tracer, analyzer
14,82
68
8
18
24
14,83
65
25
61
2
3
18
26
24
132
38,72
91
40
24,87
60
39
57
18
127
127
52
52
8
Vapor pressure, H2 0 142
Quality assurance
14
"Warm-up" time
Analyzer
Calibrator
Perm tube
Water
Condensation
Vapor pressure
Zero air
Generator
Requirements
Supply
Zero check
31
55
42
18
142
37
36
36
91
147
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO,
EPA-600/4-78-024
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Use of the Flame Photometric Detector Method for
Measurement of Sulfur Dioxide in Ambient Air
A Technical Assistance Document
5. REPORT DATE
May 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
W. Gary Eaton
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
Research Triangle Park, N.C.
10. PROGRAM ELEMENT NO.
1 HD 621
27709
11. CONTRACT/GRANT NO.
68-02-2433
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 9/76 - 5/78
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This Technical Assistance Document is intended to serve as a source-
book of information and outlines of good practice for operation and
calibration of ambient air S0~ detection analyzers based on the measurement
principle of Flame Photometric Detection (FPD). This is accomplished
through the identification and control of critical parameters affecting
the operation and calibration of FPD analyzers. The document may be
used with analyzers which measure total sulfur, as well as with new
specific models which have been designated as equivalent methods by
EPA.
so2-
This document is to be used in conjunction with the instrument
manufacturer's instruction manual. The document consists of six sections:
(1) Introduction to FPD principle, (2) Installation and startup of the
analyzer, (3) Calibration sources and their air supplies, (4) Procedures
for multipoint dynamic calibration, (5) Procedural aids, and (6) References
and Index.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*
*
Sulfur Dioxide
Air Pollution
* Calibrating
* Flame Photometry
Ambient Air
SOp Measurement
S02 Calibration
S02 Permeation Device
Quality Control
07 B
13B
14B
14B
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
147
20. SECURITY CLASS (Thispage)
i' -FioH
22. PRICE
EPA Form Z220-1 (9-73)
------- |