Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 264)

Model 9110TH NOx Analyzer Troubleshooting & Repair
Teledyne Analytical Instruments 244
7.5.20. PMT TEMPERATURE
PMT temperature should be low and constant. It is more important that this temperature
is maintained constant than it is to maintain it low. The PMT cooler uses a Peltier
thermo-electric cooler element supplied with 12 V DC power from the switching power
supply PS2. The temperature is controlled by a proportional temperature controller
located on the preamplifier board. Voltages applied to the cooler element vary from 0.1
to 12 VDC. The temperature set point (hard-wired into the preamplifier board) will vary
by ±1
C due to component tolerances. The actual temperature will be maintained to
within 0.1° C  around that set point. On power-up of the analyzer, the front panel
enables the user to watch that temperature drop from about ambient temperature down to
its set point of 6-8° C. If the temperature fails to adjust after 30 minutes, there is a
problem in the cooler circuit. If the control circuit on the preamplifier board is faulty, a
temperature of –1° C
 is reported.