Discrepancy Between Analog Output And Display - Teledyne T200 Operation Manual

Teledyne API – T200 NO/NO

12.5.7. DISCREPANCY BETWEEN ANALOG OUTPUT AND DISPLAY

06858E DCN7057
/NO Analyzer Operation Manual
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
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
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.

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.

Diffusion of oxygen into Teflon-type tubing over long distances.

PTFE or related materials can act as permeation devices. In fact, the
permeable membrane of NO

When using very long supply lines (> 1 m) between high concentrations span
gases and the dilution system, oxygen from ambient air can diffuse into the line
and react with NO to form NO

This reaction is dependent on NO concentration and accelerates with increasing NO
concentration, hence, affects linearity only at high NO levels.

Using stainless steel for long span gas supply lines avoids this problem.
If the concentration reported through the analog outputs does not agree with the value
reported on the front panel, you may need to recalibrate the analog outputs.

This becomes more likely when using a low concentration or low analog output
range.

Analog outputs running at 0.1 V full scale should always be calibrated manually.

See Section 5.9.3.2 for a detailed description of this procedure.
Troubleshooting & Service
in NO gas is common).
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permeation tubes is made of PTFE.
2
.
2
and
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