22 • 35-3010A-12 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 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 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 may be necessary for the sample draw detector.
Calibration, Oxygen Detector
This section describes how to calibrate the oxygen detector in the sample-draw detector. It
includes procedures to prepare for calibration, set the zero reading, set the fresh air 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 to set the zero reading. A 4-gas cylinder is used
to set the zero since it is already used to calibrate the CO and H
2
S channels. A 100%
nitrogen calibration cylinder could also be used to set the zero reading.
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.
For the oxygen channel, plug the voltmeter into the test points on the oxygen transmitter. Plug
the positive lead into the test point labeled TP+; plug the negative lead into the test point
labeled TP-.
4.
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 12% and a fullscale setting of 25%, the correct
output for the oxygen test points is 292 mV.
292 (mV) = (12/25) X 400 +100