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Calibration Frequency
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 CO detector
and LEL detector.
Calibration, LEL Sensor
This section describes how to calibrate the LEL 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 standard calibration gas for the LEL sensor is methane. The sample-draw detector may be
calibrated to other combustible gases such as hexane or hydrogen. Use the correct calibration
gas for your installation.
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 LEL 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
