20 • 35-3010A-09 Sample-Draw Detector
Calibration, IR CH
4
Detector
This section describes how to calibrate the IR CH
4
sensor in the sample draw detector. It
includes procedures to prepare for calibration, set the zero reading, set the response
reading, and return to normal operation.
NOTE:
This procedure describes calibration using a demand flow regulator, a zero air
calibration cylinder, and a methane calibration cylinder.
Preparing for Calibration
CAUTION:
This procedure may cause alarms at the controller. Take appropriate action to avoid
this, such as entering the calibration mode at the controller.
1.
Open the housing door.
2.
Set a voltmeter to measure in the millivolt (mV) range.
3.
Plug the voltmeter into the test points on the CH
4
transmitter. Plug the positive lead
into the test point labeled TP+; plug the negative lead into the test point labeled TP-.
4.
Use the following formula to determine the correct test points output for the
calibrating sample.
Output (mV) = (calibrating sample/fullscale) X 400 + 100
For example, with a calibrating sample of 50 %volume methane and a fullscale setting
of 100 %volume, the correct output for the CH
4
test points is 300 mV.
300 (mV) = (50/100) X 400 +100
Setting the Zero Reading
NOTE:
If you can verify a fresh air environment, it is not necessary to use the zero air
calibration cylinder to set the zero reading.
1.
Screw the regulator into the zero air calibration cylinder.
2.
Connect the calibration kit sample tubing to the regulator.
3.
Connect the sample tubing from the regulator to the inlet line at or near the INLET
fitting.
4.
Allow the gas to flow for one minute.
5.
Verify a voltmeter reading of 100 mV ± 2 mV at the CH
4
test points as described in the
Preparing for Calibration section above.
6.
If necessary, use a small flat-blade screwdriver to adjust the zero pot for the IR CH
4
channel until the voltmeter reading is 100 mV ± 2 mV.
7.
Disconnect the sample tubing from the inlet line.
8.
Unscrew the regulator from the zero air calibration cylinder. Leave the sample tubing
connected to the regulator.
