20 • 65-2397SS CO
2
Transmitter
Calibration
This section describes how to calibrate the CO
2
transmitter. It includes procedures to prepare for
calibration, set the zero reading, set the response reading, and return to normal operation.
WARNING: The controller is not an active gas monitoring device during the calibration
procedure.
NOTE:
The following procedure assumes the use of a calibration kit which includes a calibration gas
cylinder, a 100% nitrogen cylinder, a 0.5 LPM fixed flow regulator with an on/off knob, a
calibration cup for the detector, and a short piece of sample tubing to connect the regulator to
the calibration cup.
Preparing for Calibration
1. Unscrew and remove the junction box cover.
2. Set a voltmeter to measure in the millivolt (mV) range.
3. Plug the voltmeter leads into the test points on the amplifier. Plug the positive lead into the red (+)
test point; plug the negative lead into the black (-) test point.
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 2.5 %Vol. and a fullscale setting of 5 %Vol., the correct
output is 300 mV.
300(mV) = (2.5/5.0) X 400 +100
5. Screw the calibration cup onto the detector housing.
6. Place the controller into its calibration mode or disable external alarms.
NOTE:
Calibrating the CO
2
transmitter may cause alarms. Be sure to put the controller into its
calibration mode or disable external alarms before continuing.
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 of a CO
2
transmitter with a low range detector. Fresh air can be used to zero the transmitter if a 0-20% volume,
0-50% volume, or 0-100% volume detector is being used.
1. Screw the regulator into the 100% nitrogen calibration cylinder.
2. Use the calibration kit sample tubing to connect the regulator to the calibration cup.
3. Turn the regulator’s on/off knob counterclockwise to open the regulator.
4. Allow the gas to flow for one minute and verify a reading of 100 mV (±2 mV). If necessary, use
the zero pot on the amplifier to adjust the reading to 100 mV (±2 mV).
5. Turn the regulator’s on/off knob clockwise to close the regulator.
