82 DF-310E User Interface
8.6.2.2 Check/Adj Span
Note: A calibration should be performed only after the Analyzer has been operating at least
eight hours. The door should be closed when calibrating the Analyzer to keep the sensor
temperature stable.
It is not possible to perform a Span Adjustment if the TEMP OVER RANGE condition is
occurring.
The Check/Adj Span entry in the Oxygen Cal Menu, Figure 50, is used to adjust the O
2
calibration. Selecting Check/Adj Span will display the screen shown in Figure 53.
Disclaimer
The method used to correct the calibration of the Servomex Oxygen Analyzer for
measurement in non-nitrogen background gases is derived from a well known theoretical mass
transfer equation. This equation accounts for the change in oxygen diffusion rates through
different gases.
Although significant empirical work has been done in this field, it is generally accepted that
the equation may be only 85-90% accurate. In addition, there is further error introduced when
correcting for a "multi" component background gas. This may result in an additional 3-5%
error. Correcting the calibration (for all combinations of background gases) using theoretical
means has its limitations.
An alternate method when using a non-nitrogen or "multi" component background gas is to
obtain a certified oxygen calibration standard which has been prepared in a background gas
which models the average process sample. In this case any possible error introduced in using
the theoretically derived correction factor is eliminated. Caution must still be used, however,
as certified standards may also have inaccuracies associated with them.
Questions regarding the calculation of a background gas correction factor for a specific
application should be directed to the local Servomex Business Center.
NOTE: In light gas (H
2
or He) backgrounds, the diffusion rate of oxygen will be greater than that in nitrogen,
resulting in a higher absolute current generated by the sensor. If the sample contains an oxygen concentration
near the high-end of the instrument (e.g. 80 ppm on a 0-100 ppm unit), and consists of a light gas background,
the current generated by the sensor may be too much for the electronics to source and will effectively put the
instrument out of range. In such a case, it would be appropriate to use an analyzer of the next highest range (e.g.
0-500 ppm). Consult Servomex for application specific details.
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