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Model 9110T NOx Analyzer Troubleshooting & Service
Teledyne Analytical Instruments 277
If the response offset test functions for NO (NO OFFS) or NO
X
(NOX OFFS) are greater than
150 mV, a reaction cell contamination is indicated.
Clean the reaction cell as described in Section 11.3.9.
12.5.2. NO RESPONSE
If the instrument shows no response (display value is near zero) even though sample gas is supplied
properly and the instrument seems to perform correctly.
1. Carry out an electrical test with the ELECTRICAL TEST procedure in the
diagnostics menu, see Section 12.7.12.2.
If this test produces a concentration reading, the analyzer’s electronic signal
path is correct.
2. Carry out an optical test using the OPTIC TEST procedure in the diagnostics
menu, see Section 12.7.12.1.
If this test results in a concentration signal, then the PMT sensor and the
electronic signal path are operating properly.
If the 9110T passes both ETEST and OTEST, the instrument is capable of
detecting light and processing the signal to produce a reading.
Therefore, the problem must be in the pneumatics or the ozone generator.
3. Check if the ozone generator is turned on.
Usually, the analyzer issues a warning whenever the ozone generator is turned
off.
Go to SETUP-MORE-DIAG-ENTR, then scroll to the OZONE GEN OVERRIDE
and see if it shows ON.
If it shows OFF, turn it ON and EXIT the DIAG menu.
If this is done and the ozone flow is correct, the analyzer should be properly
supplied with ozone unless the generator itself is broken.
4. Confirm the lack of response by supplying NO or NO2 span gas of about
80% of the range value to the analyzer.
5. Check the sample flow and ozone flow rates for proper values.
6. Check for disconnected cables to the sensor module.
7. If NO
2
signal is zero while NO signal is correct, check the NO/NOx valve
and the NO
2
converter for proper operation.
12.5.3. UNSTABLE ZERO AND SPAN
Leaks in the 9110T or in the external gas supply and vacuum systems are the most common source of
unstable and non-repeatable concentration readings.