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TROUBLESHOOTING & REPAIR PROCEDURES
11.3. Calibration Problems
11.3.1. Mis-Calibrated
There are several symptoms that can be caused by the analyzer being
mis-calibrated. This condition is indicated by out of range Slopes and Offsets as
displayed through the test functions and is frequently caused by the following:
•
Contaminated Span gas. This can cause a large error in the slope and a small
error in the offset. Span gas contaminated with a major interferent such as
Mercury Vapor, will cause the analyzer to be calibrated to the wrong value.
Also could be caused if the Span gas concentration entered into the analyzer
during the calibration procedure is not the precise concentration value of the gas
used.
•
Dilution calibrator not set up correctly or is malfunctioning. This will also cause
the slope, but not the zero to be incorrect. Again the analyzer is being calibrated
to the wrong value.
•
Too many analyzers on the manifold. This can cause either a slope or offset
error because ambient gas with its pollutants will dilute the zero or span gas.
•
Contaminated Zero gas. This can cause either a positive or negative offset and
will indirectly affect the slope. If contaminated with O3 it will cause a positive
offset.
11.3.2. Non-Repeatable Zero and Span
As stated earlier, leaks both in the M400E and in the external system are a
common source of unstable and non-repeatable readings.
1. Check for leaks in the pneumatic systems as described in Section 9.3.4. Don't
forget to consider pneumatic components in the gas delivery system outside the
M400E. Such as:
A change in Zero Air source such as ambient air leaking into zero air line, or;
A change in the Span Gas concentration due to Zero Air or ambient Air
Leaking into the Span Gas line.
2. Once the instrument passes a leak check, do a flow check (see Section 9.3.5) to
make sure adequate sample is being delivered to the optical bench assembly.
254
Model 400E Ozone Analyzer
Instruction Manual
P/N 04316 Rev: B
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