Teledyne Mixchek - Helium / Oxygen mixture analyzer - Manual (Page 22)

Setup MIXCHEK
Teledyne Analytical Instruments 22
control. A typical sample system, which provides for calibration gas
switching is shown in Figure 2-7.
If using a calibration gas other than air, the concentration of oxygen
in the calibration gas must be known and for best results, should be
approximately 80-100% of the range of interest. For instance if the
analyzer is to be used to typically measure oxygen levels close to 50%
then the calibration gas should have an oxygen concentration between
40-50%.
To successfully calibrate this instrument you should have the
following items on hand:
• Calibration gases (air and 100% helium gas source)
• Means for controlling the calibration gas flow
• Trim pot tool (see Parts Listing in Appendix) or small
screwdriver
To calibrate the oxygen analyzer:
Span Calibration (oxygen sensor)
1. Adjust the flow rate of the air source to 0.2–2 SLPM. prior to
attaching it to the gas inlet of the analyzer.
2. When the oxygen display reading stabilizes (approximately 1
minute) adjust the oxygen display to read 20.9% using the
O2 Span control on the front panel.
To calibrate the helium analyzer:
• The helium analyzer will typically provide 1% accuracy or
better for 30 or more days without adjustment.
• The helium & air table can be used to check the accuracy of
the helium analyzer section after the oxygen span has been set.
• Always calibrate the zero setting on the helium analyzer
prior to calibrating the span setting.
• Always validate the calibration using the helium & air table
after calibration at two or more points (ref. sec. A.3)
Zero Calibration (helium sensor)
Note: To zero the helium sensor, there must be no residual gases
other than air in the sample line of the instrument. Step 1
below is designed to purge the sample line using air.