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Troubleshooting & Repair Teledyne API - Model 200EH/EM Operation Manual
266
In some cases with excessive sample moisture, the oxidized molybdenum metal chips inside the
converter cartridge may bake together over time and restrict air flow through the converter, in which
case it needs to be replaced. To avoid this problem, we recommend the use of a sample gas
conditioner (Section 5.10). Section 9.3.6 describes how to replace the NO
2
converter cartridge.
With no NO
2
in the sample gas and a properly calibrated analyzer, the NO reading is negative, while the
NO
2
reading remains around zero. The converter destroys NO and needs to be replaced.
With no NO
2
in the sample gas and a properly calibrated analyzer, the NO
X
reading is significantly
higher than the actual (gas standard) NO concentration. The converter produces NO
2
and needs to be
replaced.
11.5.17. O
3
GENERATOR
The ozone generator can fail in two ways, electronically (printed circuit board) and functionally (internal
generator components). Assuming that air is supplied properly to the generator, the generator should
automatically turn on 30 minutes after the instrument is powered up or if the instrument is still warm. See
Section 10.3.6 for ozone generator functionality. Accurate performance of the generator can only be determined
with an ozone analyzer connected to the outlet of the generator. However, if the generator appears to be
working properly but the sensitivity or calibration of the instrument is reduced, suspect a leak in the ozone
generator supply air.
A leak in the dryer or between the dryer and the generator can cause moist, ambient air to leak into the air
stream, which significantly reduces the ozone output. The generator will produce only about half of the nominal
O
3
concentration when run with moist, ambient air instead of dried air. In addition, moist supply air will produce
large amounts of nitric acid in the generator, which can cause analyzer components downstream of the
generator to deteriorate and/or causes significant deposit of nitrate deposits on the reaction cell window,
reducing sensitivity and causing performance drift. Carry out a leak check as described earlier in this chapter.
11.5.18. BOX TEMPERATURE
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 to check the
BOX_TEMP signal voltage
using the
SIGNAL I/O function under the DIAG Menu (Section 6.13.1). At about 30° C, the signal
should be around 1500 mV.
We recommend to use a certified or 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.
11.5.19. 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 ±1C 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.
04521C (DCN5731)