35-3001A-07-03 Methane/Hydrogen Sulfide Sample-Draw Detector • 21
Calibration Frequency
Although there is no particular calibration frequency that is correct for all applications, a calibration
frequency of every 3 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 3 months for the H
2
S detector and every 6 months for the infrared
CH
4
detector.
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 6 months is adequate for the H
2
S detector and every 9 to 12 months is adequate for the
infrared CH
4
detector.
If an application is very demanding, for example if the environment is not well controlled, then
more frequent calibration than every 3 months for the H
2
S detector and every 6 months for the
infrared CH
4
detector may be necessary.
Calibration, IR CH
4
Sensor
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% volume and a fullscale setting of 100% volume,
the correct output is 300 mV.
300 (mV) = (50/100) X 400 +100
