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Model 9110T NOx Analyzer Troubleshooting & Service
Teledyne Analytical Instruments 306
permeation tube output will be significant. In this case, a dryer for the supply air is recommended (dew
point should be –20° C or less).
The permeation tube of the internal span gas generator option is heated with a proportional heater circuit
and the temperature is maintained at 50°C ±1C. Check the front panel display or the IZS_TEMP
signal voltage using the SIGNAL I/O function under the DIAG Menu (Section 5.9.1). At 50° C, the
temperature signal from the IZS thermistor should be around 2500 mV.
12.7.17. TEMPERATURE SENSOR
12.7.17.1. Box Temperature Sensor
The box temperature sensor (thermistor) is mounted on the motherboard below the bottom edge of the
CPU board when looking at it from the front. It cannot be disconnected to check its resistance.
Box temperature will vary with, but will usually read about 5° C higher than, ambient (room)
temperature because of the internal heating zones from the NO
2
converter, reaction cell and other
devices.
To check the box temperature functionality, we recommend checking the BOX_TEMP signal voltage
using the SIGNAL I/O function under the DIAG Menu (Section 12.1.3).
At about 30° C, the signal should be around 1500 mV.
To check the accuracy of the sensor, use a calibrated external thermometer / temperature sensor to
verify the accuracy of the box temperature by:
Placing it inside the chassis, next to the thermistor labeled XT1 (above connector J108) on
the motherboard.
Compare its reading to the value of the test function PMT TEMP.
12.7.17.2. PMT Temperature Sensor Control
The temperature of the PMT should be low and constant. It is more important that this temperature is
maintained at a constant level than it is to be a specific temperature.
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 ±2
The actual temperature will be maintained to within 0.1° C around that set point.
To check the operation of the PMT temperature control system:
1. Turn off the analyzer and let its internal components cool / heat to ambient
temperature.
2. Turn on the analyzer.
3. Set the front panel to show the PMT TEMP test function (see Section 4.1.1).
The temperature should fall steadily to 6-10° C.