35-3001A-09 Oxygen/Hydrogen Sulfide Sample-Draw Detector • 23
Calibration, H
2
S Sensor
This section describes how to calibrate the hydrogen sulfide 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 H
2
S
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 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
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 hydrogen sulfide 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.
