Non-Linear Response - Teledyne T200 User Manual

NON-LINEAR RESPONSE

The analyzer 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 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 5.6.11.
• 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
•
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 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
ammonia derivatives break through to the reaction cell.
• Check the contents of the ozone cleanser and replace as necessary (Section
5.6.3).
• This also will affect linearity mostly at the low level.
• Sample inlet may be contaminated with NOx exhaust from this or other analyzers.
Verify proper venting of the pump exhaust.
•
Span gas overflow is not properly vented and creates a back-pressure on the
•
sample inlet port.
Also, if the span gas is not vented at all and does not supply enough sample gas,
•
the analyzer may be evacuating the sample line.
Ensure to create and properly vent excess span gas.
•
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