35-3001A-10 Oxygen/Carbon Monoxide Sample-Draw Detector • 27
Calibration, CO Sensor
This section describes how to calibrate the carbon monoxide 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.
NOTE:
If you can verify a fresh air environment, it is not necessary to use the zero air calibration
cylinder to set the zero reading.
2. Screw the regulator into a zero air calibration cylinder.
3. Set a voltmeter to measure in the millivolt (mV) range and plug the leads into the CO amplifier.
Plug the positive lead into the red (+) amplifier test point; plug the negative lead into the black (-)
amplifier test point.
4. Use the following formula to determine the correct test points output for the test sample.
Output (mV) = (calibrating sample/fullscale) X 400 + 100
For example, with a test sample of 50 ppm and a fullscale setting of 300 ppm, the correct output is
167 mV.
167 (mV) = (50/300) X 400 +100
Setting the Zero Reading
1. Connect the sample tubing from the demand flow regulator to the sample-draw detector’s inlet
line.
This step is not necessary if you verified a fresh air environment earlier in this
procedure.
2. Allow the sample-draw detector to draw sample for one minute.
3. Verify a voltmeter reading of 100 mV (± 2 mV).
4. If necessary, use a small flat-blade screwdriver to adjust the zero potentiometer until the voltmeter
reading is 100 mV (± 2 mV). If you used a zero air calibration cylinder to set the zero reading,
proceed to step 5. If you verified a fresh air environment, proceed to the next section, Setting the
Response Reading.
5. Disconnect the sample tubing from the inlet line.
6. Unscrew the regulator from the zero air calibration cylinder.
Setting the Response Reading
1. Screw the regulator into the CO 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.
