RKI Instruments 35-3001A-05-02 - Manual (Page 23)

35-3001A-05-02 Carbon Dioxide Sample-Draw Detector • 19
Calibration
This section describes how to calibrate the carbon dioxide 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. 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 260 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, it is necessary to use a
calibration kit with a 100% nitrogen cylinder to set the zero signal of the carbon dioxide sample-
draw detector.
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).
6. Disconnect the sample tubing from the inlet line.
7. Unscrew the regulator from the 100% nitrogen calibration cylinder.
Setting the Response Reading
1. Screw the regulator into the carbon dioxide 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. When the reading on the voltmeter stabilizes, verify that the reading matches the response
reading (±2 mV) you determined earlier.
5. If necessary, use the span potentiometer on the amplifier to adjust the reading to match the
correct response reading.