Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 263)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 243
To avoid this problem, we recommend the use of a sample gas conditioner
(Section 5.10). Section 6.4.4 describes how to replace the NO2 converter
cartridge.
 With no NO2 in the sample gas and a properly calibrated analyzer, the NO
reading is negative, while the NO2 reading remains around zero. The
converter destroys NO and needs to be replaced.
 With no NO2 in the sample gas and a properly calibrated analyzer, the NOX
reading is significantly higher than the actual (gas standard) NO
concentration. The converter produces NO2 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 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 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 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.