Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 242)

Model 9110TH NOx Analyzer Troubleshooting & Repair
Teledyne Analytical Instruments 222
 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 7.5.
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 mV to 150 mV for
offsets). See Section 13 on how to carry out a low-level hardware
calibration.
7.3.5. INABILITY TO ZERO - NO ZERO BUTTON
In general, the 9110TH/M will not display certain touch screen buttons whenever the
actual value of a parameter is outside of the expected range for that parameter. If the
calibration menu does not show a ZERO button when carrying out a zero calibration, the
actual gas concentration must be significantly different from the actual zero point (as per
last calibration), which can have several reasons.
 Confirm that there is a good source of zero air.
 Check to make sure that there is no ambient air leaking into zero air line.
Check for leaks in the pneumatic systems as described in Section 7.5.
7.3.6. NON-LINEAR RESPONSE
The 9110TH/M was factory calibrated to a high level of NO and should be linear to
within 1% of full scale. Common causes for non-linearity are:
 Leaks in the pneumatic system. Leaks can add a constant of ambient air,
zero air or span gas to the current sample gas stream, which may be
changing in concentrations as the linearity test is performed. Check for
leaks as described in Section 7.5.
 The calibration device is in error. Check flow rates and concentrations,
particularly when using low concentrations. If a mass flow calibrator is
used and the flow is less than 10% of the full scale flow on either flow
controller, you may need to purchase lower concentration standards.