Trace Oxygen Analyzer | Operation 4 | |
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4.4Calibration of the Analyzer
The analyzer must be calibrated prior to its use. For most applications where the desired range of measurement is 0 to 1 ppm, we recommend the analyzer be calibrated using a span gas as detailed below:
Span Gas Calibration
Before the cell is ready for calibration, it must be purged with semple gas to low oxygen levels preferably below 0.2 ppm. However, if the oxygen contact of the sample gas is higher than 0.2 ppm, a zero gas such as nitrogen with oxygen levels below 0.2 ppm may be required.
The recommended span gas concentration is between 7.0 to 9.0 ppm oxygen in nitrogen, and will require calibration be performed in the
Air Calibration
If desired, a newly installed cell may be calibrated in air to 209,000 ppm. However, this practice is generally not recommended as the cell may take 24 hours or longer to recover to less than 0.2 ppm after being exposed to air for about 3 to 5 minutes.
4.4.1 Zero Cal
The
Generally, the value of the zero offset is part of the oxygen reading of the sample gas as shown by the analyzer readout. As an example, a reading of 0.5 ppm oxygen may include 0.4 ppm oxygen in the sample gas and a 0.1 ppm zero offset.
The determination of the zero offset requires the use of oxygen free gas to the analyzer. We recommend the use of nitrogen gas with a scrubber to assure oxygen levels below 0.02 ppm.
The user may decide to eliminate the zero offset for improved accu- racy. If so desired the analyzer is equipped to provide this function. How- ever, we do not recommend carying out the cal zero during the first 10 days of the operation of the cell.
Teledyne Analytical Instruments |