18 • 35-3010RK-07 Sample-Draw Detector
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 oxygen
and H
2
S sensors and every 6 months for the IR CH
4
sensor in the sample draw 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 for the oxygen and H
2
S sensors and every 12
months for the IR CH
4
sensor is adequate for the sample draw detector.
If the application is very demanding, for example if the environment is not well
controlled, then more frequent calibration than every 3 months for the oxygen and H
2
S
sensors and every 6 months for the IR CH
4
sensor may be necessary for the sample draw
detector.
Calibration, H
2
S Detector
This section describes how to calibrate the H
2
S detector 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 4-gas 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 leads into the test points in the AMP 2 section of the main circuit
board. Plug the positive lead into the test point labeled CAL+2; plug the negative lead
into the test point labeled CAL-2.
4.
Use the following formula to determine the correct test points output for the H
2
S
calibrating sample.
Output (mV) = (calibrating sample/fullscale) X 400 + 100
For example, with a calibrating sample of 25 ppm H
2
S and a fullscale setting of 100
ppm H
2
S, the correct output for the H
2
S test points is 200 mV.
200 (mV) = (25/100) X 400 +100
