Model 200E Instruction Manual Troubleshooting & Repair
slope, -20 to 150 for offsets). See Section 11.6.5 on how to carry out a low-level
hardware calibration.
11.3.5. Inability to Zero - No ZERO Key
In general, the M200E will not display certain keyboard choices 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 key when carrying out a zero calibration, the actual gas concentra-
tion 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. If the IZS option is installed,
compare the zero reading from the IZS zero air source to a zero air source using
NO
X
-free air. Check any zero air scrubber for performance. It may need to be
replaced (Section 9.3.7).
• 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 11.5.
11.3.6. Non-Linear Response
The M200E 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 concentra-
tions as the linearity test is performed. Check for leaks as described in Section 11.5.
• 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.
• 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 filter
chemical will let compounds such as HNO
3
and ammonia derivatives break through
to the reaction cell. Check the contents of the ozone filter cartridge and replace as
necessary. This also will affect linearity mostly at the low level.
• Sample inlet may be contaminated with NO
X
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. Make sure to create
and properly vent excess span gas.
044100102 Rev A 201
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