16 • 35-3001A-05-XX CO
2
Sample-Draw Detector
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. Open the housing door.
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. Screw the demand flow regulator into the 100% nitrogen calibration cylinder.
5. Connect the calibration tubing from the demand flow regulator to the inlet fitting. Gas will begin to
flow.
6. Allow the sample-draw detector to draw sample for one minute.
7. Verify a voltmeter reading of 100 mV (± 2 mV).
8. If necessary, use a small flat-blade screwdriver to adjust the zero potentiometer until the voltmeter
reading is 100 mV (± 2 mV).
9. Remove the calibration tubing from the inlet fitting, then reconnect the sample tubing to the inlet fitting.
10. Remove the voltmeter leads from the test points.
11. Close the housing door.
Maintenance
This section describes maintenance procedures. It includes preventive maintenance procedures. This section
also includes procedures to troubleshoot the sample-draw detector, replace components of the sample-draw
detector, adjust the low flow setting, and remove the particle filter’s tubing stub.
Preventive Maintenance
This section describes a preventive maintenance schedule to ensure the optimum performance of the sample-
draw detector. It includes daily and biannual procedures.
Daily Visual Checks
1. Verify that the Pilot LED is on.
2. Verify that the flowmeter indicates a flow rate of approximately 1.0 SCFH. If necessary use the sensor
flow control valve to adjust the flow rate to 1.0 SCFH. Turn the valve’s knob counterclockwise to
increase the flow and clockwise to decrease the flow.
3. Verify a display reading at the controller of the background concentration of CO
2
. Typical background
concentrations of CO
2
vary from about 300 to 600 ppm (0.03 - 0.06% volume) depending on location.
The 0 - 5,000 ppm and 0 - 5% volume ranges will show a reading in fresh air. The 0 - 50% and 0 - 100%
volume ranges should not show a reading in fresh air. Investigate significant changes in the display
reading.
Biannual Calibration
Calibrate the sample-draw detector as described in “Calibration” on page 22.
