Teledyne T200, Руководство по эксплуатации, Страница: 247 / 425

Teledyne API
– T200 NO/NO
2
/NO
X
Analyzer Operation Manual Troubleshooting & Service
245

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 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.

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
2
permeation tubes is made of PTFE.

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
2
.

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.
12.5.7. DISCREPANCY BETWEEN ANALOG OUTPUT AND DISPLAY
If the concentration reported through the analog outputs does not agree w ith 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.
06858E DCN7057