35-3001A-07-03 Methane/Hydrogen Sulfide Sample-Draw Detector • 23
Calibration, H
2
S Sensor
This section describes how to calibrate the H
2
S sensor in 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:
Calibrating the sample draw detector may cause alarms. Be sure to put the controller into
its calibration program or disable external alarms before continuing.
NOTE:
This procedure describes calibration using a demand flow regulator.
Preparing for Calibration
NOTE:
If you can verify a fresh air environment, it is not necessary to use a zero air calibrating
sample to set the zero reading at the controller.
1. Follow the instructions in the controller’s operator’s manual for entering calibration mode.
2. Screw the regulator into the zero air calibration cylinder.
3. Open the housing door.
4. Set a voltmeter to measure in the millivolt (mV) range.
5. Connect the voltmeter to the test points on the H
2
S amplifier.
Plug the positive lead into the red (+) amplifier test point; plug the negative lead into the black
(-) amplifier test point.
6. 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 25 ppm and a fullscale setting of 100 ppm, the correct
output is 200 mV.
200 (mV) = (25/100) X 400 +100
Setting the Zero Reading
1. Connect the sample tubing from the demand flow regulator to the sample-draw detector’s inlet
fitting.
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 fitting.
6. Unscrew the regulator from the zero air calibration cylinder.
