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Teledyne API Model 200A NO
X
Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
9.3.8 NO
x
Sensor Module
Table 9-9-20 and Table 9-9-21 show the assembly of the NO
x
sensor module.
9.3.8.1 PMT
The PMT detects the light emitted by the reaction of NO with ozone. It has a gain of about
500,000 to 1,000,000. It is not possible to test the detector outside of the instrument in the field.
The best way to determine if the PMT is working is by using Optic Test. OT operation is
described in Section 9.1.3.3.
The basic method to diagnose a PMT fault is to eliminate the other com
ponents using ET, OT
and specific tests for other sub-assemblies.
9.3.8.2 Reaction Cell Temp
The reaction cell temperature is controlled by the CPU. It operates by reading a thermistor
amplifier on the 01086 Status/Temp board. The CPU controls the temperature by toggling a bit
on the V/F board. The V/F board TTL logic controls a solid state switch on the Switch Board in
the PSM. The switched 115VAC comes out of the PSM to a connector near the underside of the
reaction cell. A warning message may be present during initial warm-up or if the connector is
not plugged in after cleaning the reaction cell.
9.3.8.3 Preamp Board
The NO
x
Preamp Board is a multifunction board providing circuitry to support the following
functions.
1.
Preamp, buffer amplifier, physical range control hardware for the PMT detector.
2.
Precision voltage reference and voltage generation, and control for the PMT - HVPS
inside the sensor module.
3.
Constant current generator and adjustment for the Optic Test LED.
4.
Voltage generation and adjustment for Electric Test.
5.
Thermistor amplifier, control signal generation for the PMT cooler.
The setup and adjustment of items 1-4 above is covered in the Factory Calibration procedure in
Section 9.1.6. Item 5 has no adjustable features.
9-62
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