AeroChem TP-258
OPERATIONS HANDBOOK
FOR THE AEROCHEM PROTOTYPE
CONTINUOUS CHEMILUMINESCENCE
NO MONITOR
Final Report
Richard J. Ronco and Arthur Fontijn
May 1971
Prepared for
AIR POLLUTION CONTROL OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Research Triangle Park, N.C. 27709
Contract CPA 70-79
Research Laboratories, Inc.
SYBRON CORPORATION
Princeton, New Jersey
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AeroChem TP-258
OPERATIONS HANDBOOK
FOR THE AEROCHEM PROTOTYPE
CONTINUOUS CHEMILUMINESCENCE
NO MONITOR
Final Report
Richard J. Ronco and Arthur Fontijn
May 1971
Prepared for
AIR POLLUTION CONTROL OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Research Triangle Park, N. C. 27709
Contract CPA 70-79
. ~- Research Laboratories, Inc.
SYBRON CORPORATION
Princeton, New Jersey
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TP-258
FOREWORD AND ACKNOWLEDGMENT
Under our contract CPA 22 -69 -11 (August 1968 -September 1969), the
feasibility of using the NO/03 chemiluminescent reaction for selective quanti-
tative monitoring of NO had been demonstrated. Under the present contract
CPA 70-79 (May 1970-May 1971) a prototype ambient air NO monitor based
on the NO/03 reaction has been designed, fabricated, and delivered to the
APCO Project Officer. The present report gives a detailed discussion of this
prototype instrument as well as design considerations.
We are indebted to R. K. Stevens, APCO Project Officer on both con-
tracts, as well as to J. A. Hodgeson and A. E. O'Keeffe of APCO for useful
advice. The measuring electronics package has been designed with the aid of
W. W. Brenner and H. S. Reichard, AeroChem Electronics Cons ultants. We
have also benefited from discussions with A. J. Sabadell, H. F. Calcote, and
F. H. Raab of AeroChem and with several technical representatives of manu-
facturers, whose equipment is incorporated in the monitor. M. D. Shaltis has
capably assisted in the assembly of the instrument.
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TP-258
TABLE OF CONTENTS
Page
FOREWORD AND ACKNOWLEDGMENT iii
LIST OF FIGURES vii
1. SPECIFICATIONS 1
II. GENERAL DESCRIPTION 3
A. Principle of Measurement 3
E. Instrument Functions 4
Ill. DETAILED DESCRIPTION 5
A. Gas Handling System 5
B. Light Detection System 6
C. Calibration Functions 7
D. Electronics 8
IV. OPERATING INSTRUCTIONS 11
A. Description of Panels and Controls 11
B. Installation 12
C. Operation 13
D. Maintenance 14
E. Troubleshooting 16
V. DESIGN CONSIDERATIONS AND TESTS 18
A. Stainless Steel Gas Flow System 18
B. Photomultiplier Tube Selection 18
C. Measurement of the Background Signal 20
D. Linearity of Response 21
VI. REFERENCES 22
VII. LIST OF MANUFACTURERS 23
v
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TP - 258
LIST OF FIGURES
Figure Page
1. SCHEMATIC OF THE CHEMILUMINESCENCE NO DETECTOR 25
2 SPECTRAL DISTRIBUTION OF NO/03 EMISSION 26
3 BLOCK DIAGRAM OF PROTOTYPE NO ANALYZER 27
4 FRONT VIEW OF MONITOR 28
5 REAR VIEW OF MONITOR 29
6 RIGHT INSIDE VIEW OF MONITOR 30
7 TOP INSIDE VIEW OF MONITOR 31
8 LEFT INSIDE VIEW OF MONITOR 32
9 SPECTRAL RESPONSE OF EMI 9558 A PHOTOMULTIPLIER
TUBE 33
10 AUTOMATIC REZERO AND SIGNAL CALIBRATION SEQUENCE 34
11 BLOCK DIAGRAM OF MEASURING ELECTRONICS PACKAGE 35
12A CURRENT-TO-VOLTAGE CONVERTER CIRCUIT 36
12B DC AMPLIFIER/FILTER CIRCUIT 37
12C CONTROL/SERVO LOGIC CIRCUIT 38
12D HIGH VOLTAGE RELAY CIRCUIT 39
12E . MOTOR DRIVER CIRC UIT 40
vii
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TP-258
I. SPECIFICATIONS
PRINCIPLE OF
MEASUREMENT
Gas phase chemiluminescence.
TYPE OF MONITORING
Continuous.
USEFUL CONCENTRATION
RANGE
::: 2 ppb* to ::: 200 ppm NO in air.
ATMOSPHERIC INTERFERENCES
None.
MEASURING RANGES
Five decade ranges:
O-lOppb O-lOOppb
0- 1 ppm 0- 10 ppm
O-lOOppm.
SPAN
Continuously adjustable multiplication of
any decade range by factors from 1 to 10.
ACCURACY
Determined by the accuracy oi the
calibration gas sample (typically :I: 5 'Yo).
ELECTRONICS
All solid state.
READ OUT
Large scale analog panel meter.
RECORDER OUTPUT
0-1 VD C.
CALIBRATION
Automatic every 8 hours; manual as
desired.
TIME LAGt
50 seconds (for normal inlet).
5 seconds (for auxiliary sample inlet).
RISE TIME ~
10 seconds.
*
t
Defined as the minimum signal detectable above background noise.
Defined as the lapse in time between the introduction of a sample and the
initial meter response.
~
Defined as the period of time, following the time lag, required for a
signal to reach 90 % of its ultimate value.
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TP-258 ,
POWER REQUIREMENTS
115 V AC (l % regulated) 60 Hz, 400 W
(exclusive of vacuum pump). '
VACUUM PUMP
Explosion proof, 3.5 CFM mechanical,
115 VAC, 60 Hz, 700 W.
DIMENSIONS
l8lth X 22"w X 20" d.
WEIGHT
110 lbs.
EXTERNAL CONNEC TIONS
Vacuum pump.
Oxygen and calibration gas cylinders.
Line voltage regulator.
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TP-258
II.
GENERAL DESCRIPTION
A.
Principle of Measurement*
A schematic design of the chemiluminescence detector is shown in
Fig. 1. The air (analyte) being monitored and the second r~actant, partially
ozonated oxygen (I::: 0.,5 % v/v), enter the reaction vessel (p I::: 1 Torr) through
separate inlets. Rapid mixing occurs and a chemiluminescent reaction takes
place:
NO + 03 - NOz * + Oz
(1)
NOz* - NOz + hv
(2)
The intensity of the light emitted is measured by the photomultiplier tube and
associated read-out devices (current meter and recorder). After calibration
with samples of known concentration, a continuous record of the concentration
of the pollutant in air is obtained.
The light intensity, I, of the NO/03 reaction is given by:3
I ;: k[NO][ 03]/P
(3)
in which
k = rate coefficient (proportionality constant)
[ ] = denotes concentrations
P = Pressure
Thus at a constant pressure and 03 concentration, the intensity, and hence the
phototube current reading, is linearly proportional to the amount of NO flow-
ing through the system.
The spectral distribution of the NO/03 chemiluminescent emission is
shown in Fig. 2. The phototube being used is responsive to radiation over the
0.35 to 0.85 I.L range. Since as Fig. 2 shows the NO/03 radiation is emitted
at wavelengths larger than 0.6 .... a light -filter passing only such radiation is
placed in the light path (see Fig. 1), thus minimizing the 'chances for accidental
measurements of interfering emissions by other reactions.
*
Fo'r a more detailed description see the reports on the feasibility study,
Rcis. 1 and 2.
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B.
Instrument Functions
The basic functions are shown schematically in Fig. 3. *' They may be
subdivided into the gas flow system, the light detection system and the calibra-
tion functions.
The principal gas handling system consists of an ambient air (sample)
flow line and an ozonated oxygen flow line. The volume flow rate is controlled
at a preset value by the sonic orifices. The gases mix in the reactor and the
flow is maintained by the mechanical vacuum pump. For use of the instrument
as a research tool, an auxiliary sampling system has been provided, through
which the flow can be controlled manually with a needle valve (under normal
conditions this line is closed by means of a toggle valve).
The light detection system consists of the thermo-electrically cooled
photomultiplier tube, the phototube high voltage power supply, and the measur-
ing electronics package to which are connected the current meter (calibrated
in terms of NO concentration) and the recorder output.
To calibrate the instrument the ambient air inlet can be closed by the
3 -way solenoid valve, A, and be replaced by a flow containing a known amount
of NO (~alibration gas). To rezero the electronics the sample flow side is
clused off entirely by the solenoid valve B. Both these calibration functions
a.:-, carried out automatically at fixed intervals controlled by the time pro-
grOimmer; they can also be initiated by the operator by means of pushbuttons
loca.ted on the front panel.
*
A detailed description is given in Section III.
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III.
DET AILED DESCRIPTION
Figures 4 and 5 show the front and rear panels of the monitor. Fig-
ures 6, 7 and 8 are photographs of the inside of the instrument showing the
location of the major components, to be discussed below.
A.
Gas Handling System
1
.. .
Reactor
The one lite r spherical reactor has been fabricated from 16 gauge
type 316 stainless steel; it has a reactant nozzle inlet flange on the top, a
vacuum outlet tube on the bottom, and an optical window on the side. A
therm.0couple vacuum gauge (Hastings Raydist VT-4/DV4R), consisting of a
noble ;l"lCLal thennocouple and a corrosion-resistant housing, is attached to
the V,i.'::U;J.nl outlet tube (1-1/8 inch o.d. type 316 stainless steel). The 2 inch
o. d. suartz optical window is held in place by an ethylene propylene O-ring
flange. *
2..
Gas Feed Lines
The gas feed line functions can best be followed from Fig. 3. The
tubing used is 0.25 inch o.d. (0.016 inch wall) type 316 stainless steel.
a. Primary Reactant (Analyte) - Ambient air is drawn into the sys-
tem through a coarse filter (Hoke No. 6325G4 Y) and then through the three-
way stainless steel solenoid valve A (Asco No. 832069 VH). The valve
normally passes ambient air, but is automatically switched every 8 hours to
allow the calibration gas to flow during the calibration cycle. The airt passes
through a 5 micron sintered stainles s steel filter (Hoke No. 6321 G4 Y) and
*
These O-rings are specifically resistant to ozone. Bulletin 5721, Parker
Seal Co. (Culver City, Calif.) 1970.
t
The presence of HzO vapor in the reactor does not interfere with the NO meas-
urement. 1, Z However, it is conceivable that during very warm and humid
periods HzO might condense in the flow lines and interfere with the NO flow.
If problems are encountered during such periods the dryer provided with
the instrument (stored on the bottom plate, see Fig. 6) should be filled with
indicating activated alumina and be installed in the space provided in the
flow line just upstream of the 5 micron filter.
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TP-258
then through the sonic flow orifice* (Richard Bird Co., Model RB-282J). The
flow through this orifice is 0.8 cc (STP) sec -1. The orifice is located on the
downstream side of the filter holder (Hoke No. 632164Y) for maximum protec-
tion against clogging. The air then passes through the stainless steel solenoid
valve 13 (Asco No. 8262C3SVH) which is automatically closed during the periodic
background current suppression cycle. Finally, the air enters the reactor
through the Pyrex nozzle.
A common flow path is provided for the air and calibration gas where-
ever possible. The calibration gas is best delivered to the instrument at a
pressure of about 2 psi by a two-stage corrosion resistant regulator. , A low-
pressure regulator (Conoflow Corp. HIOXTI014K) located inside the instrument
(Fig. 3) reduces this pressure to atrnospheric, to provide the same flow condi-
tion for the calibration gas as for the analyte air.
An auxiliary gas inlet line has been added to the primary reactant line.
The use of this input will allow the introduction of a gas flow directly into the
reactor without going through the sonic orifice -filter system. The gas flow is
controlled with a needle valve and a toggle valve located inside the instrument.
These valves are accessible through the removable panel on the right hand side
of the instrument.
b. 03/01. Feed Line - Cylinder 01. passes through ~ stainless steel dryer
filled with indicating type activated alumina; a Plexiglas flange cover is pro-
vided to allow visible observation of the condition of this drying agent. The 03
is prodllced at a concentration of s:::: O. S % v/v by passage of the Oz through the
photolytic ozonator (OREC 03VI-0/S). The remaining components such as the
low-pressure regulator, micron filter, and sonic orifice, are duplicates of the
components used in the primary reactant flow line. The 03/0Z enters the reac-
tor through a Pyrex nozzle.
B.
Light Detection System
The photomultiplier tube housing (Products for Research TE-I02 TS)
is flange mounted directly to the reactor, to allow the photocathode to be situ-
ated as close as possible to the reactor and obtain a light-tight assembly. The
housing is thermo-electrically/air cooled to -lSoC and regulated to within
:t O. SOC by an external power supply. The radiation eritering the housing passes
through a specially designed thermopane window which pr,ovides a thermal break
between the reactor and the phototube and prevents window fogging. 1'11«' .
*
We have considered thermostating the flow orifices. However, normal
roorn temperature variations of :I: 5°C would produc:e only a :t 1 % change
in gas flow rate (and a comparable change'in sigJl::!l), which appears too
rn) lIor to require correction.
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TP-258
thermopane window consists of a Corning CS 2-60 light filter disc and a clear
Pyrex dis c separated by a Plexiglas cylinder and is filled with dry nitrogen.
The filter cuts off radiation of A < 6100 'A... The housing also provides electro-
static and electromagnetic shielding for the phototube.
The radiation is monitored with an EM! 9558A tria1ka1i photomultiplier
tube, operated at 1950 VDC. The spectral response curve is shown in Fig. 9'.
The power supplies 'used in the light detection system are discussed in the
Electronics Section (III. D.).
C.
Calibration Functions
1.
Automatic Calibration
In order to rezero and calibrate the instrument the time programmer
master control (Automatic Timing and Controls 324 COIL2CRIAOIX) engages
an automatic sequence every 8 hours. This 5 minute sequence is controlled,
by the time programmer sequence control (Automatic Timing and Controls
324C07E3ERIAOIX) and is shown schematically in Fig. 10. This 5 minute
sequence consists of four steps: steps a and b form the rezero cycle and steps
c and d the nitric oxide signal cycle.
Step a - The solenoid valve, B (Fig. 3), closes the primary reactant
line. At the end of the rezero cycle it returns the instrument to the normal
operating condition.
Step b - The electronic autoba1ance cycle is engaged and automatically
adjusts the background* signal to zero by applying a current of reverse polar-
ity. t The balance cycle is held in the engaged position for 30 seconds, to time
average the background signal. During this balance cycle the most sensitive
range (0 -10 ppb) is automatically selected regardless of the (front pane i) range
switch setting. Wh'en the cycle is complete ,the range will automatically return
to the setting indicated by the range switch.
Step c - The 0 -1 pprn range is automatically selected regardless of the
range switch setting. When the cycle is complete the range will automatically
return to the setting indicated by the range switch.
t
That signal produced by the unidentified radiation resulting from passage
of ozonated oxygen through the reactor.
Such balance currents are also commonly referred to as. "current offset",
"current suppression" and "buck out".
*
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TP-258
Step d - The solenoid valve, A, is energized and the calibration gas*
is allowed to flow through the reactor, thus yielding the calibration point on
the meter and recorder.
2.
Manual Initiation Options
a. The full automatic calibration cycle can be initiated at any time
by depressing the AUTO CALIB button on the front panel. Once engaged the
cycle will run in exactly the same manner as described under automatic cali-
bration (Section III. C. 1). This procedure does not influence the automatic 8-
hour initation.
b. The electronic autobalance cycle, can be engaged by first clos-
ing valve Band then pushing the BALANCE button on the front panel.
3.
Manual Calibration Sample Introduction
Calibration flows can also be manually introduced into the system
at any time. We have found the following procedure to be very convenient:
Fill a :::: 25 cc graduated syringe with a known concentration of calibration gas
(e. g. from the calibration cylinder), remove the needle and connect the syringe
to the sample inlet with a short piece of flexible tubing. The calibration sam-
ple will then be drawn into the monitor at a rate which can be directly ,meas-
ured by observing the rate of movement of the plunger. The concentration of
calibration gas remains constant until the syringe is empty.
D.
Electronics
1.
Measuring Electronics Package
The basic functions of the measuring electronics package are to
amplify the photomultiplier tube current with an electrometer type amplifier
and to reduce the noise component of the signal. A 6-inch panel meter (analog
type) is mounted on the front panel and monitors the measuring electronics
*
The gas recommended for calibration is Nz containing:::: 0.5 ppm of NO.
In our work this gas contained 0.39 :!: 0.02 ppm NO, according to the
supplier's (Scott Research Laboratories, Plumsteadville, Pa.) analysis.
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TP-258
output. This meter is calibrated in parts per billion of nitric oxide. A 0 -1 VDC
recorde r output connection is provided on the rear panel. The measuring elec-
tronics package also contains a phototube overload protection circuit, a zero
s uppres s ion circuit to balance the instrument noise and the automatic range
selection for the calibration cycle. A block diagram is given in Fig. 11, and
complete schematics are shown in Figs. 12A-12E.
a. Current Input and Ranging - The measuring electronics package,
Fig. II, is connected to the photomultiplier tube socket at the ANODE connec-
tion with a coax cable (RG58/U). This current is amplified, filtered and read
out on the front panel meter. Five current ranges can be manually selected
with the decade RANGE switch on the front panel: 0 -10 ppb, 0 -100 ppb,
0-1 ppm, 0-10 ppm, 0-100 ppm. The SPAN ADJUST control (normally set to
1.00 on the dial) is continuously adjustable and can be used to set any full scale
range within the operating limits of the instrument.
NOTE: Do not use SPAN ADJUST settings below 1.00 since the current meas-
uring electronics is non-linear at such settings.
b. Phototube Protection Circuit - The phototube would be damaged if
the maximum allowable anode current (1mA) were exceeded. Therefore a pro-
tection device (located in the measuring electronics package), which removes
the high voltage from the photomultiplier tube is built in. This device, Fig. 11,
consists of a current sensing circuit and a high voltage relay, which can also
be tripped by the front panel PMT OFF button.
CAUTION: The phototube protection device and the PMT OFF button do not
turn off the high voltage power supply and dangerous voltage thus remains
inside the instrument.
c. Balance Circuit - A noise current suppression device, Fig. II, has
been built into the measuring electronics package to suppress the background
signal to near zero. This noise current suppression will hereafter be referred
to as balance. Since the background signal is not a pure DC or a steady signal
but rathe t a tandom low frequency composite, the background can best be con-
sidered as a b
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TP-258
. The balance circuit also contains an offset: current interrupt switch
which is operated by keeping the ANODE CURRENT pushbutton on t.he front panel
depressed. In this way, the phototube anode current is observed directly on the
front panel meter (read "nAil for "ppb"), which gives a measure of the a mount
of offset current being used. Knowledge of the phototube current is helpful in
troubleshooting.
2.
Phototllbe Power Supply
The phototube high voltage power supply (Computer Power Systems
2500 N/12S4) is mounted inside the instrument on the rear panel (Fig. 8). The
output voltage is preset at 1950 VDC. * This high voltage is supplied to the
phototube by a coax cable (RG59/U) through the high voltage relay.
CAUTION: High voltages exist at the power supply output connector, cable, and
, high voltage relay.
3. Cooled Housing Power Supply
This power supply, Fig. 8, provides the 6 VDC power for the
thermoelectric heat pump of the phototube housing and the line voltage for the
fan motor used to circulate air over the thermoelectric heat exchanger. This
supply remains on as long as power is supplied to the monitor.
4.
Ozonator Power Supply
This power supply is contained in the ozonator housing (see Section
III. A. 2).
CAUTION: The ozone lamp is powered by a 5000 V AC high voltage transforI"n.er.
A safety device (cover interlock switch) turns off the line voltage if the ozonator
cover is removed. .Care should be taken not to come in contact with the
transformer.
*
Fo r the intended operation of the rnonitor this voltage should not be changed.
However, it may be useful to mention that a 5 % adjushnent screw is located
on this power supply (see F.ig. 8) and that installation of other internal pro-
gramming resistors allows the selection of other voltages in the range -500
to -2000 Volts (for details see the Computer Power Systems instruction
manual supplied with the instrument).
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TP-258
IV.
OPERATING INSTRUCTIONS
A.
Description of Panels and Controls
Front Panel (see Fig. 4)
1.
METER
The meter continually displays the concentration
of nitric oxide being measured by the instrument.
The scale is calibrated from 0 -10 pa rts pe r
billion.
METER RESET
Zeros the meter when held depressed.
RANGE SWITCH
Selects the instrument measuring range from
anyone of five full scale ranges: Xl, X 10, X l(j
X 103, X 104, corresponding to 10, 102, 103, 104
and 105 ppb full scale.
SP AN ADJ UST
Used to set any full scale range between the
decade range switch settings.
POWER ON
Connects and disconnects the line voltage to the
electronics measuring package and the phototube
power supply. Power is on when pushbutton is
lighted.
PMT ON
Turns on the high voltage to the phototube by
operating the high voltage relay. Phototube
power is on when pushbutton is lighted.
PMT OFF.
Turns off the high voltage to the phototube by
tripping the high voltage relay. Phototube
power is off when this button is lighted.
BALANCE
Engages the balance circuit, zeroing Lh(: 1J1:,;l.l'll-
rnenL. When this button is lighted the insLrurnenL
is balancing.
AUTO CALIB
Engages the time programmer and calibrates the
instrument. When this button is lighted the
instrument is calibrating.
.
ANODE CURRENT
When held depressed shows the phototube anode
current on the meter; under these conditions
read "nanoamps II in place of "ppb". This button
does not light up.
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VACUUM GAUGE
2.
Rear Panel (see Fig. 5)
RECORDER OUTPUT
RECORDER' ADJUST
AIR INLET
CALIBRA TION
INLET
OXYGEN INLET
AUXILIAR Y AIR
IN LE T
VACUUM
CONTROL SWITCH
FOR SOLENOID
VALVE B
B.
Ins tallation
Shows the reactor pressure.
0-1 VDC.
Follows the front panel meter.
Used to match the recorder to the meter.
In normal operation the sample air is drawn
into the instrument through this connector.
The calibration gas flows into the instrument
through this connector.
The Oz to be ozonated flows in through this
conne ctor 0
Air can be drawn into the instrument through
this connector.
Connector to the vacuum pump.
In normal operation this switch should be in the
"open" position. When closed analyte NO will
not flow into the reactor.
Step a - Place the instrument on a suitable support such as a table or
bench, so that air can circulate through the monitor. Cooling air is taken in
through louvers in the bottom of the monitor, and is exhausted through the
louvered side. For good air circulation allow at least 6 inches of free air
space on the left (louvered) side of the monitor.
Step b - Connect the vacuum pump to the monitor using the connectors
and tubing provided. A three -foot long stainless steel tube is supplied with the
instrument and can be cut to any desired length. .
NOTE: The 3.5 CFM vacuum pump (Edwards ES 100) supplied with the instru-
ment is filled with Dow Corning Fluorosilicone (FS 1265 30CS) fluid. Regular
hydrocarbon base oils should no~ be used since they deteriorate when pumping
ozonated oxygen and may explode.
Step c - Connect a good commercial grade oxygen cylinder via a pres-
sure regulator to the OXYGEN INLET connector on the rear panel. The inlet
pressure should be about 2 psi. A standard size (:::: 240 cu. ft.) cylinder is
I '
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TP-258
recornmended for operational convenience.
NOTE: Purge the gas line well before connecting to the monitor. .
CAUTION: Inlet pressures above 5 psi can damage the pressure regulator
ins ide the monitor.
Step d - Connect the air supply to be monitored to the AIR INPUT
connector on the rear panel.
NOTE: To minimize'response time the connection between the air inlet and
air source should be kept as short as pos sible and be made of narrow tubing
(e. g. O. 1 inch i. d.).
Step e - Connect a supply of calibration gas at a pressure of about 2 psi
to the CALIBRATION INLET connector on the rear panel. For ambient air
monitoring calibration gas having a concentration of no more than about 0.5 ppm
NO in Nz is recommended.
CAUTION: Inlet pressures above 5 psi can damage the pressure regulator in-
s ide the monitor.
C.
Operation
Step a - Turn the solenoid valve "B" control switch (rear panel) to the
"closed" position.
Step b - Turn the RANGE switch to the X 104 position.
Step c - Set the SPAN control to 1.00 (1 in window, 0 on dial).
Step d - Turn on the vacuum pump by connecting it to a standard
115 Volt AC electrical outlet.
Step e - Con~ect the instrument power cord (rear panel) to a regulated
115 Volt AC outlet using the regulator provided.
NOTE: To minimize electronic noise this regulator should be positioned several
feet away from the instrument.
CAUTION: The instrument should be connected to an electrical ground using the
lhl'l.:('-prong plug pro"vidcd.
Step f - Depress the POWER ON button on the front panel.
will light up.
The button
Step g - Allow at least two hours for the phototube to automically cool
to -15°C. During this period the phototube dark current will decrease by about
two orders of magnitude. In the following seven days the phototube dark current
will gradually decrease by about one more order of magnitude. Hence in the
first week the instrument will not be at full sensitivity.
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TP - 258
Step h - Hold the METER HESET button depressed and adjust the
reading to zero using the mechanical meter zero screw.
St.ep i - DepresR the PMT ON button which will light up.
Step j - Move the range switch to a lower scale so that a meter read-
ing is obtained.
Step k - Depress the BALANCE button which will light up. The light
will go off when the zeroing operation is complete. Repeat if necessary.
NOTE: During automatic calibration this button may light up intermittently
as the instrument repeats the zeroing operation.
Step 1 - Turn the solenoid valve B control switch (rear panel) to the
"open" position.
Step m - The instrument is now measuring the level of nitric oxide
flowing in from the ambient. To read-off the NO concentration set the RANGE
switch and SPAN ADJUST to the ranges desired.
Step n - The instrument will automa.tically rezero and give a calibra-
tion signal every 8 hours (d. Section Ill. C. 1). If calibration is desired at any
other time push the AUTO CALIB button; the instrument then will rezero itself
and give a calibration point. 1£ the calibration point does not register at the
correct reading, adjust the calibration potentiometer as described in Section
IV. D. 2. .
NOTE: The AUTO CALIB botton has to be held depressed for about 7 see before
it enga ges. Engagement is indicated by the light remaining on after the button
has been released.
D.
Maintenance
1.
Planned Maintenance
o~ DRYER -
The indicating type, activated alumina drying
agent (viewed through the window on the dryer
top) should be changed as needed. The average
life of one charge corresponds to at least three
n1.onths continuous operation.
AIR DR YER -
If the air dryer (Section III. A. 2) is in use the
~.ctivated alumina (indicating type) drying agent
should be refilled as needed. The dryer has a
large enough capacity to last for at leaRt 3
weeks when the relative humidil y is 100 % at
35°C.
~J.4
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TP-258
Ol CYLINDER-
Change the oxygen cylinder before the cylinder
is cornpletely empty to avoid possible damage
to the ozonat'or under vacuum conditions. A
standard size cylinder will last for about nine
weeks, based on continuous flow rate of
0.8 c -: (STP) sec -1 and a cylinder capacity of
::::: 240 cu. ft.
NOTF~: Purge the oxygen line well after con-
necting a new cylinder.
VACUUM PUMP-
Check the oi11eve1 and drive -belt wear
occasionally.
NOTE:: The vacuum pump is filled with fluoro-
silicone oil. Dot not use hydrocarbon oils, cf.
Section IV. B.
CAUTION: Toxic vapors may be produced from
this oil by heating; use. with adequate ventilation.
GAS FLOWS -
Check the vacuum gauge occasionally. The
gauge pressure should be about 1.0 Torr. A
change in gas flow conditions, such as a pa rtiall y
obstructed flow line, will show up on the vacuum
gauge.
ANODE CURRENT -
Check the phototube ANODE CURRENT occasion-
ally with the solenoid valve B closed. Under
these conditions this current should not exceed
400 nA as this exceeds the balance circuit capa-
bility and is indicative of a malfunction (see
Section IV. E).
FILTERS -
Change the coarse and fine filters (Fig. 3) as
needed, depending on local ambient conditions.
The filters can best be cleaned in an ultrasonic
cleaner.
2.
Signal Calibration
An internal calibration potentiometer is provided in the electronics
measuring package (board 3 marked CALIBRATION POT (Fig. 7)). This
potentiometer is preset to match th<: current indicated on the panel meter
against a known concentration of nitric oxide. The potentiometer setting should
not be changed unless the calibration point on the meter does not agree with the
known calibration gas concentration. In that case perform the following steps:
15
-------
TP-258
Step a- Turn the solenoid valve "B" control switch (rear panel) to the
CLOSED position.
Step b - Wait one minute; depress the BALANCE button which will
light up. The light will go off when the balance cycle is complete. Repeat if
necessary.
Step c - Move the RANGE switch and the SPAN ADJUST to obtain a
range of 0 -1 ppm.
Step d - Flow in the calibration gas (= 0.5 ppm NO in Nz). Adjust the
potentiometer until the reading on the meter scale matches the known concen-
tration of NO in the calibration gas.
E.
Troubleshooting
Procedures to guide troubleshooting are given on the following chart:
16
-------
Symptom
1. Panel meter at zero. no needle movement.
z.
Anode current increase, in excess of
1 IoLA.
3.
PMT high voltage off as indicated by a totaJ
loss of signal and by the front panel
pushbuttons.
4.
Reactor pressure is one half of the normal
pressure (=0.5 Torr).
5.
Balance cycle engages (as indicated by the
lighted BALANCE button) but will not
disengage.
6.
The reactor pressure is higher than
= 3.0 Torr.
......
-J
TROUBLESHooTlNG CHART
Possible Cause
a) Blown fuse (rear panel).
b) Blown fuse in PMT high voltage power supply
a) PMT housing power supply output too low.
b) Lii(ht leak in the light detection system
c) Normal air circulation through the n1Onitor has
been rest ricted.
a) A concentration of nitric oxide in excess of
1000 ppm has been introduced into the monitor,
tripping the phototube overload device.
b) A light leak has developed in the light detection
system.
a) The BALANCE-MEASURE switch is in the
BALANCE position.
b) The oxygen gas cylinder is empty.
c) A sonic flow orifice is clogged restricting the
normal flow.
a) The balance cycle was engaged while the moni-
tor was measuring an NO concentration in
excess of I ppm.
b) The balance current offsetting limit has been
exceeded by a light leak raising the anode cur-
rent above I IoLA.
A leak in the gas handling system has developed.
Correction
Replace fuse.
Replace fuse.
Check fuse. check the high voltage output, repai r if
necessary.
Tighten th,' O-ring bPtwel'n-thc PMT housing and th" react.H.
Allow adequate air flow. Set' instalJation instructions.
Wait fifte('r; (15) minut(.~. r{'s(.t by dC'pressing lhe PMT o;-~
butt on.
Tight.." the O-ring between the PMT housing and the reactor.
Return the switch to the MEASURE position.
Replace the oxygen cylinder.
Remove the oriiice/fiIter holder and clean in an ultrasonic
cleaner.
Step I - Depress the PMT OFF button and then depress the
PMT ON button.
Move the solenoid valve B control switch to the
CLOSED position. Wait one minute. Balance.
Return the switch to the OPEN position.
Follow Steps 1 and Z.
Ste p l -
Move the BALANCE-MEASURE switch to the BALANCE
position. Isolate the leak by standard leak detection
methods and repair.
-------
TP-258
v.
DESIGN CONSIDERATIONS AND TESTS
A.
Stainless Steel Gas Flow System
A spherical Pyrex reactor had been used in the feasibility study.l, z
However, a metal reactor appeared more suitable for a rugged compact design
for the prototype instrument and moreover is easier to assemble and
disassernble.
To evaluate this idea a 1 liter type 316 stainless steel reactor was
substituted for the Pyrex reactor in the apparatus used in the feasibility study.
This substitution yielded a slightly lower background noise (measured by flow-
ing only ozonated oxygen through the apparatus) and did not affect the NO/03
signal strength. The limit of sensitivity thus is slightly improved using the
stainless steel reactor, which was subsequently incorporated in the prototype
instrument.
Other parts, such as the phototube housing, were also first tested on
the feasibility study apparatus, before deciding whether to incorporate them
into the prototype monitor.
B.
Photomultiplier Tube Selection
On the basis of the available manufacturers I literature and in consulta-
tion with several phototube manufacturers, a number of tubes were borrowed
for a series of tests. These tests were performed on the research apparatusl,z
under identical system conditions, using a Keithley 602 electrometer and maxi-
mum background current suppression.. The results of this comparison are
given in the following table:
18
-------
o
PHOTOMULTIPLIER TUBE COMPARISON AT -20 C*"
~
~
. I
N
U1
ex>
----
Tota 1 Maximum
Applied Dark Current, Background Sensitivity.,
PMT Voltage, V A Cur rent, A ppb NO Cost, $
EMI 955RQA 1400 3X 10-9 3X 10-8 4 700
EMI 9659A 2000 4 X 10-10 4 X 10-9 3 900
EMI 965RA 2000' 2 X JO..7 1 X 10-6 15-20 -/00
RCA C31000E 2ROO 3 X 10-8 4 X 10-7 15-20 750
RCA 7164R Selected 2000 ) X 10-10 1 X 10-9 75 200
*Differenc.es between individual tubes occur in any given tube type. However, the manu-
facturers loaned us the best available tubes for this comparison, which therefore has
q ua 1 ita t i v e val i d it Y .
~
~
-------
TP-258
On the basis of these tests both the EMI 9558 QA and 9659 A tubes
appeared suitable for incorporation into the prototype. However, the 9659 A
also had to be rejected since the signal received from this tube at NO concen-
trations below about 30 ppb cannot be detected with the prototype electronics
(lowest current range is 10 nA full scale; higher sensitivity would have added.
considerably to the instrument cost).
Tests on the prototype monitor' showed the 9558 QA noise level at
1400V (where the siN is most suitable for detection of weak signals) to be an
order of magnitude less than the noise in the chemiluminescence signal. As
a result we found phototube gain to be the controlling factor in achieving the
lowest limit of sensitivity and the best results were obtained with 9558 family
tubes operated near their maximum allowable voltage (2000 V). A number
of 9558 QA and A tubes* then were compared and the one with the highest gain
was incorporated in the prototype.
c.
Meas urement of the Background Signal
The technique used in the prototype for measuring the background signal
is to close solenoid valve B, i. e. to allow only the ozonated oxygen (secondary
reactant) to flow through the reactor.t Since this measurement is thus made at
half the total flow rate and pressure used when measuring NO, a test of the
validity of this procedure was required.
The test used was to flow O2 in through the auxiliary gas inlet line.
Under this condition no NO flows into the reactor, but the total flow and pres-
sure are the same as when valve B is opened and air is being sampled. No
difference in signal could be observed between this condition and the primary
reactant side closed-off condition, obtained during this test by closing the toggle
valve in the auxiliary inlet line.
It must be concluded that the instrument reading obtained in norrnal
operation when valve B is closed gives the true background signalo
*
Apart from the extended ultraviolet response of the QA (quartz envelope),
which is of no use in the present application. the 9558 QA and A tubes are
identical.
t
Under these conditions the signal measured is a combination of phototubc
dark current and unidentified light emission due to the 01.103 flow.
?O
-------
TP -258
D.
Linearity of Response
The linearity of response was tested in the same manner as during the
feasibility study"'~ i. e. by injecting known samples of NO into an exponential
dilution flask (connected to the auxiliary air inlet). * No deviation from linear-
ity over the 2 ppb to 200 ppm range could be observed. Above 200 ppm devia-
tions from linearity begin to occur.
*
The meter readings obtained from given samples were found to be the
same whether they were introduced through the auxiliary or the normal
air inlet as long as the same flow rate was maintained. For this inlet
system comparison the samples were introduced as described in
Section III. C. 3.
21
-------
TP-258
VI.
REFERENCES
1.
Fontijn, A., Sabadell, A. J. and Ronco, R. J., "Homogeneous Chemi-
. luminescent Measurement of Nitric Oxide with Ozone. Implications for
Continuous Selective Monitoring of Gaseous Air Pollutants," Anal. Chern.
42, 575 (1970).
2.
Fontijn, A., Sabadell, A. J. and Ronco, R. J., "Feasibility Study for the
Development of a Multifunctional Emission Detector for Air Pollutants
Based on Homogeneous Chemiluminescent Gas Phase Reactions, II Aero-
Chern TP-217, Final Report, Contract CPA 22-69-11, September 1969.
3.
Clyne, M.A.A., Thrush. B.A. and Wayne, R.P.. "Kinetics of the Chemi-
luminescent Reaction between Nitric Oxide and Ozone, II Trans. Faraday
Soc. 60, 359 (1964).
4.
Clough, P.N. and Thrush, B.A., "Mechanism of Chemiluminescent
Reaction between Nitric Oxide and Ozone," Trans. Faraday Soc. 63, 915
( 1967).
??
-------
TP-258
VII. LIST OF MANUFACTURERS
Manufacturer
or Vendor
Amersil, Inc.
HiHs ide, N. J.
07205
API Instruments Co.
Chesterland, Ohio 44026
Automatic Switch Co. (ASCO)
Florham Park, N. J.
Automatic Timing & Controls, Inc.
King of Prussia, Pa. 19408
Be cl\.lTlan Ins t r ument s
Fullerton, Calif. 92634
Cornpute r Power Systems, Inc.
Sunnyvale, Calif. 94086
Conoflow Corp.
Blackwood, N. J.
08012
Edwards High Vacuum, Inc.
Grand Island, N. Y. 14072
Gencom Division
Varian/EMI
Plainview, N. Y.
11803
Hastings -Raydist Co.
Hampton, Va. 23361
Ozone Research & Equipment
Corporation (OREC)
Phoenix, Ariz. 85019
Parker Seal Co.
Culver City, Calif.
90230
Products for Research, Inc.
Danvers, Mass. 01923
R. H. Bird Co.
Waltham, Mass.
02154
Item
REAC TOR WINDOW
PANEL METER
SOLENOID V ALVES
TIME PROGRAMMER
MOTOR POTENTIOMETER
PHOTOTUBE POWER SUPPLY
LOW PRESSURE REGULATORS
VACUUM PUMP
PHOTOTUBE
VACUUM GAU'GE
OZONATOR
O-RINGS
PHOTOTUBE HOUSING
SONIC ORIFICE
23
-------
~v
~~~~.
~q,. ~v
~o ~
~~~ ~
~ ~~
o (C'~ ('\0
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V ~./
OPTICAL
WINDOW
CALIBRATED
LEAKS
REACTOR
f)
'.
.'
'.
68-89A
POWER
SUPPLY
PHOTOTUBE
~
PRESS~RE
GAUGE
MECHANICAL
VACUUM
PUMP
N
U1
LIGHT
FILTER
READ-OUT
FIG. 1 SCHEMATIC OF THE CHEMILUMINESCENCE NO DETECTOR
-------
N
'"
:>-
I-
-
en
z 100
1LJ
I-
Z
1LJ
>
-
I-
-------
AMBIENT AIR
COARSE FILTER
COARSE FILTER
CALIBRATION
GAS
TIME
PROGRAMMER
N
-J
FIG. 3
I I
i :
o I
I i
o 0
! I
I 0
o I
I .
o I
I .
o I
I .
VALVE
VALVE
SOLE NOlO
SONIC ORIFICE
MICRON FILTER
OZONATOR
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PHOTOTUBE
NO NOZZLE
03 NOZZLE
r----j
--! I
- -l ! L
I I .
i !
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.
I
OPTICAL
WINDOW
~
VACUUM
PUMP
MEASURING
ELECTRONICS
-----------
BLOCK DIAGRAM OF PROTOTYPE NO ANAL YZER
70-12SA
OXYGEN
COOLED HOUSING 'I
POWER SUPPLY
HIGH VOLTAGE
POWER SUPPLY
---~RECORDER OUTPUT
- ---METER
-------
r--
71-55
N
00
FIG. 4
FRONT VIEW OF MONITOR
-------
.
,";;" . AUXILIARY AIR. '.N~U.T
W'.tlIIIII':'_!
8\
N
-.0
o
o
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8
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..
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'AEROCHEM RESEARCH LABORATORIES INC,'
p, 0, BO' 12
PRINCETON. NEW JERSE Y 08540
FIG. 5
REAR VIEW OF MONITOR
..
-
@
_:1'.""11"."""'~-
~
...
t Jf.
71- 56
II
~,
-------
71-53
w
o
OZONE INLE
AIR INLET
ORIFICE HOLDER (OZONE)
SONIC ORIFICE HOLDER (AIR)
GAS INLET
FLANGE
AIR DRYER
(STORED)
c:=:>
VACUUM GAUGE THERMOCOUPLE:=J7
l OZONATOR
FIG. 6 RIGHT INSIDE VIEW OF MONITOR
COARSE
FILTER
AUXILIARY
AIR INLET
:: .~
LOW PRESSURE
REGULATOR
TO
VACUUM
PUMP
-------
PHOTOTUBE POWER SUPPLY
RECORDER OUTPUT
71-52
LOW PRESSURE REGULATORS
COARSE FILTERS
MEASURING
ELECTRONICS
---
PHOTOTUBE HOUSING---"-
POWER SUPPLY
RANGE and SPAN SWITCHES-.!
v.>
......
FIG. 7 TOP INSIDE VIEW OF MONITOR
SOLENOID
VALV E B
CALIBRATION
POTENTIOMETER
-------
71-54
W
N
PHOTOTUBE HOUSING POWER SUPPLY
MEASURING ELECTRONICS 7
PUSHBUTTON
CONTROLS
PHOTOTUBE
HOUSING
TIME
PROGRAMMER
OZONATOR
PHOTOTUBE POWER SUPPLY
FIG. 8 LEFT INSIDE VIEW OF MONITOR
-------
69-156A
28
~
0
24 ~
u
z 2.0
!!!
~ u
-
0 u..
20 u..
.. L1J 1.0
>-
u ~
Z ::J
I.LJ ....
- 16 z
~ ~ 0
::J
u.. a 0.8 1.0 1.2
u..
I.LJ WAVELENGTH, microns
:E
::>
~
z
-------
w
,p.
STEP
d
c
b
a
71-51
I
REZERO CYCLE I NITRIC OXIDE SIGNAL CYCLE
I
I
I CLOSED
I OPEN
I
I SOLENOID VALVE A
I
I
I
I
I ON OFF
I
I AUTOMATIC
.
. RANGE SELECTION
I
I
I
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ON OFF I
I
I BALANCE
I
I
I
I
CLOSED OPEN: SOLENOID VALVE B
..... I
I I I I I
I I I
o
2
6
3
4
5
TIME, min.
FIG. 10 AUTOMATIC REZERO AND SIGNAL CALIBRATION SEQUENCE
-------
/tJpd-
IM!r;
fMT
I.>
~,
l-j2-/~ - -T - - - - - RJI-;;e-~);~'X",r;-: - - - - - - - -'I
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FIG. 11 BLOCK DIAGRAM OF MEASURING ELECTRONICS PACKAGE
-
-
Err:?;- s/ t7a/
(0/711'0/ /SerVo Logic
:> Hom
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FIG. 12A CURRENT-TO-VOLTAGE CONVERTER CIRCUIT
-------
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FIG. 12B DC AMPLIFIER/FILTER CIRCUIT
37
-------
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22
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------- |