RKI Instruments 35-3001A-01-01 - Manual (Page 22)

18 • 35-3001A-01-01 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 infrared combustible gas sample draw
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 where 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 methane 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.
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. 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).
4. If necessary, use a small flat-blade screwdriver to adjust the zero potentiometer until the