35-3001A-13-XX CO
2
/CO Sample-Draw Detector • 25
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 every 6 months for the infrared CO
2
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 CO detector and every 9 to 12 months is adequate for the infrared CO
2
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 CO detector and every 6 months for the infrared CO
2
detector may be
necessary.
Calibration, IR CO
2
Sensor
This section describes how to calibrate the IR CO
2
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.
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.
2. Open the housing door.
3. Set a voltmeter to measure in the millivolt (mV) range.
4. Connect the voltmeter to the test points on the IR CO
2
amplifier.
Plug the positive lead into the red (+) amplifier test point; plug the negative lead into the black (-) amplifier
test point labeled.
5. 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 2,000 ppm and a fullscale setting of 5,000 ppm, the correct output
is 300 mV.
260 (mV) = (2000/5000) X 400 +100
Setting the Zero Reading
Since there is a background of CO
2
in air of typically 300 - 600 ppm (0.03 - 0.06% volume), it is necessary to use
a calibration kit with a 100% nitrogen cylinder to set the zero signal for the 0 - 5,000 ppm and 0 - 5% volume
versions. Fresh air can be used to set the zero signal for the 0 - 50% and 0 - 100% volume versions.
1. Screw the regulator into a 100% nitrogen calibration cylinder.
2. Connect the sample tubing from the demand flow regulator to the sample-draw detector’s inlet line.
3. Allow the sample-draw detector to draw sample for one minute.
4. Verify a voltmeter reading of 100 mV (± 2 mV).
5. If necessary, use a small flat-blade screwdriver to adjust the zero potentiometer until the voltmeter reading is
100 mV (± 2 mV).
