18 • 35-3001A-14 Methane Sample-Draw Detector
Calibration Frequency
Although there is no particular calibration frequency that is correct for all applications, a calibration
frequency of every 6 months is adequate for most sample draw detector applications. Unless experience in a
particular application dictates otherwise, RKI Instruments, Inc. recommends a calibration frequency of
every 6 months.
If an application is not very demanding, for example detection in a clean, temperature controlled
environment, and calibration adjustments are minimal at calibration, then a calibration frequency of every 9
to 12 months is adequate.
If an application is very demanding, for example if the environment is not well controlled, then more
frequent calibration than every 6 months may be necessary.
Calibration
This section describes how to calibrate the IR CH
4
sensor of the sample-draw detector. It includes
procedures to prepare for calibration, set the zero reading, set the response reading, and return to normal
operation.
The IR CH
4
sensor is calibrated to methane.
NOTE:
This procedure describes calibration using a demand flow regulator.
Preparing for Calibration
1. Follow the instructions in the controller’s operator’s manual for entering calibration mode.
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.
2. Screw the regulator into a zero air calibration cylinder.
3. Open the housing door.
4. Set a voltmeter to measure in the millivolt (mV) range.
5. Connect the voltmeter to the test points on the IR CH
4
amplifier.
Plug the positive lead into the red (+) amplifier test point; plug the negative lead into the black (-)
amplifier test point labeled.
6. 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% LEL and a fullscale setting of 100% LEL, the correct
output is 300 mV.
300 (mV) = (50/100) X 400 +100
Setting the Zero Reading
1. Connect the sample tubing from the demand flow regulator to the sample-draw detector’s inlet line.
This step is not necessary if you verified a fresh air environment earlier in this procedure.
2. Allow the sample-draw detector to draw sample for one minute.
3. Verify a voltmeter reading of 100 mV (± 2 mV).
