Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 218)

Troubleshooting & Repair Model 9110E Instruction Manual
204 M9110E Rev B
• Carry out an optical test using the OPTIC TEST procedure in the diagnostics menu,
see Section 6.7.5. If this test results in a concentration signal, then the PMT sensor
and the electronic signal path are operating properly. If the M9110E 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.
• If NO
2
signal is zero while NO signal is correct, check the NO/NO
X
valve and the NO
2
converter for proper operation.
11.3.3. Unstable Zero and Span
Leaks in the M9110E or in the external gas supply and vacuum systems are the most
common source of unstable and non-repeatable concentration readings.
• Check for leaks in the pneumatic systems as described in Section 11.5.1. Consider
pneumatic components in the gas delivery system outside the M9110E such as a
change in zero air source (ambient air leaking into zero air line or a worn-out zero
air scrubber) or a change in the span gas concentration due to zero air or ambient
air leaking into the span gas line.
• Once the instrument passes a leak check, do a flow check (this chapter) to make
sure that the instrument is supplied with adequate sample and ozone air.
• Confirm the sample pressure, sample temperature, and sample flow readings are
correct and steady.
• Verify that the sample filter element is clean and does not need to be replaced.
11.3.4. Inability to Span - No SPAN Key
In general, the M9110E will not display certain keyboard choices whenever the actual value
of a parameter is outside of the expected range for that parameter. If the calibration menu
does not show a SPAN key when carrying out a span calibration, the actual concentration
must be outside of the range of the expected span gas concentration, which can have
several reasons.
• Verify that the expected concentration is set properly to the actual span gas
concentration in the CONC sub-menu.
• Confirm that the NO
x
span gas source is accurate. This can be done by comparing
the source with another calibrated analyzer, or by having the NO
x
source verified by
an independent traceable photometer.
• Check for leaks in the pneumatic systems as described in Section 11.5.2. Leaks can
dilute the span gas and, hence, the concentration that the analyzer measures may
fall short of the expected concentration defined in the CONC sub-menu.
• If the low-level, hardware calibration has drifted (changed PMT response) or was
accidentally altered by the user, a low-level calibration may be necessary to get the
analyzer back into its proper range of expected values. One possible indicator of this
scenario is a slope or offset value that is outside of its allowed range (0.7-1.3 for
slope, -20 to 150 for offsets). See Section 11.6.5 on how to carry out a low-level
hardware calibration.