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Model 9110T NOx Analyzer Troubleshooting & Service
Teledyne Analytical Instruments 279
using NOX-free air. Check any zero air scrubber for performance. It may
need to be replaced (Section 11.3.4.2).
2. Check to ensure that there is no ambient air leaking into zero air line. Check
for leaks in the pneumatic systems as described in Section 11.3.12.
12.5.6. NON-LINEAR RESPONSE
The 9110T 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 11.3.12.
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.
The standard gases may be mislabeled as to type or concentration.
Labeled concentrations may be outside the certified tolerance.
The sample delivery system may be contaminated.
Check for dirt in the sample lines or reaction cell.
Calibration gas source may be contaminated (NO
2
in NO gas is common).
Dilution air contains sample or span gas.
Ozone concentration too low because of wet air in the generator.
Generator system needs to be cleaned and dried with dry supply air.
Check the Perma Pure dryer for leaks.
This mostly affects linearity at the low end.
Ozone stream may be contaminated with impurities.
An exhausted ozone cleanser chemical will let compounds such as HNO
3
and ammonia
derivatives break through to the reaction cell.
Check the contents of the ozone cleanser and replace as necessary (Section 11.3.3).
This also will affect linearity mostly at the low level.
Sample inlet may be contaminated with NOx exhaust from this or other analyzers.