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Teledyne API Model 200AU NO
X
Analyzer Instruction Manual, 02293, Rev. F
9-55
9.3.7 Flow/Pressure Sensor
The flow/pressure sensor board consists of 2 pressure sensors and a flow sensor. See Figure 9-8
for a diagram of this board. From these three sensors four values are computed and displayed on
the front panel TEST functions. They are:
1. Ozone flow - measured directly - S3, R3
2. Reaction Cell Pressure - measured directly - S2, R2
3. Sample gas pressure - measured directly S1, R1
4. Sample Flow - computed from sample pressure and reaction cell pressure S1, S2
The above pressures and flows are filtered to produce the front panel readings. There is a small
delay after adjustment for a steady reading when observing the TEST functions.
To adjust the OZONE flow:
1. Go to DIAG mode by pressing SETUP-MORE-DIAG, then select SIGNAL I/O, and
press ENTR. Select OZONE_FLOW by using NEXT-PREV keys.
2. Adjust R3 so that OZONE_FLOW reads 2000 mV. This is the coarse adjustment.
3. Press EXIT to return to the SAMPLE mode. Select the OZONE FL - TEST function. Use
a calibrated flow measuring device to make small adjustments in R3 to dial in correct flow.
To adjust the SAMPLE PRESSURE:
1. Go to DIAG mode by pressing SETUP-MORE-DIAG, then select SIGNAL I/O, and
press ENTR. Select SAMPLE_PRESS by using NEXT-PREV keys.
2. Adjust R1 to read 4100 mV, which will give approximately the correct pressure.
3. Press EXIT to return to the SAMPLE mode. Select SAMP - TEST function. Use a
calibrated absolute pressure meter to make small adjustments to R1 until the correct absolute
pressure is displayed. 29.92 in-Hg-A is the target value at sea level. The rate of decrease is
about 1"-Hg per 1000 ft of altitude.
To adjust the REACTION CELL PRESSURE:
1. Go to DIAG mode by pressing SETUP-MORE-DIAG, then select SIGNAL I/O, and
press ENTR. Select RCELL_PRESS by using the NEXT-PREV keys.
2. Adjust R2 to read 1450 mV, which will give approximately the correct pressure.
3. Press EXIT to return to the SAMPLE mode. Select RCEL - TEST function. Use a
calibrated absolute pressure meter to make small adjustments to R2 until the correct absolute
pressure is displayed. The target value is about 5 in-Hg-A for the external Thomas pump in
good condition at sea level.