Negative Concentration Display; Excessive Noise - Teledyne 6200A Manual

TAI Model 6200A SO

9.2.4 Negative Concentration Display

1. Mis-calibration. The 'zero' gas that was used to zero the 6200A contained some SO
that is it had more SO
calibration using ambient air.
2. Broken PMT temperature control circuit, causing high zero offset. Check PMT temperature
which should be 7 ± 1
3. Aging UV filter causing high stray light. Check STR. LGT reading of TEST function. It
should be less than 100 ppb.
4. Check for light leak.
5. Check for used up zero air canister if the instrument has the IZS option and the canister is
being used to zero the instrument.
6. New kicker or new reaction cell may take a week or longer of conditioning time to reach low
steady state condition.

9.2.5 Excessive Noise

Common reasons for excessive noise are:
1. Leak in pneumatic system.
2. Light leak - check the sensor module with strong light.
3. HVPS noisy - see HVPS test procedure. See Section 9.3.10.
4. Defective electronic components on preamp board. - use optic test and electric test to check
electronics, optics and observe noise.
5. Contamination of reaction cell and optical system - This can be wet air or impurities. This can be
detected by high PMT readings with zero air as sample gas. Clean reaction cell as described in
Section 8.6.
Broken PMT temperature control circuit. Check PMT TEMP - TEST function.
6. Mis-calibration. Check SLOPES in TEST function.
7. Too low UV lamp output. Should be higher than 600mV. Replace the lamp if it is lower than this
value.
8. High stray lights - UV filter is aging.
Analyzer Operator Manual, 02164, Rev. G
2
gas than that of the sample air. May also be caused by doing a zero
2
o
C.
9-25
gas -
2