Teledyne API - Model T200H/T200M Operation Manual
Troubleshooting & Service
253
•
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.
7.5.18. 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 8.3.6 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 Subsysten Checkout Section.
7.5.19. 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 using 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.
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.
07270D DCN7141