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8.3 Calibration Errors
The MAXO2 analyzers have a self test feature built into the software to
detect faulty calibrations. During calibration, if the signal from the oxygen
sensor is outside the limits stored within the instrument’s memory, a
flashing “CAL Er” is displayed. The error code is displayed to indicate
that either the sensor should be replaced or that there is a fault in the
calibration process. A few simple hints can prevent calibration errors.
If you try to adjust the analyzer display before the reading has stabilized,
the “CAL Er” may appear. For example, if the analyzer had just been
calibrated on a known high concentration of oxygen source gas and then
exposed to ambient air, you should wait until the reading has stabilized. If
you try to adjust the display to read 20.9% before the sample line has
cleared of high concentration O
2, the sensor may actually be exposed to
residual high % oxygen. The signal from the sensor would still be high
and considered “out of spec” for air, thus resulting in a “CAL Er”. The
proper procedure is to wait for the reading to stabilize before adjusting the
display. This may take 30 seconds or more.
8.4 Atmospheres of High Humidity
The MAXO2 analyzer can be used in applications where the relative
humidity of the sample gas ranges from 0 to 95%, non-condensing.
However, it should be noted that water vapor exerts its own pressure in
the same manner as oxygen does in a sample gas stream.
For example, if the MAXO
2
analyzer is calibrated in dry gas and then the
gas is humidified, the analyzer will correctly display a reading which is
slightly lower than previously displayed. This is due to the dilution of
oxygen in the sample gas by water vapor.
Gas streams of high humidity may tend to condense on the sensor.
Condensation on the sensor may eventually affect performance. For this
reason, it is recommended that the unit be used in a vertical position, with
the barb fitting pointing downward to prevent condensate from flowing
onto the sensing surface.
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