65-2424RK H
2
S Transmitter • 11
CAUTION:
Allow the transmitter to warm up for 5 minutes before you continue with the next
section, “Setting the Zero Signal”.
Setting the Zero Signal
NOTE:
If you can verify that the detector is in a fresh air environment (environment known to
be of normal oxygen content and free of toxic and combustible gases), it is not
necessary to apply zero air when verifying or setting the fresh air reading.
The procedure below describes applying zero emission air, usually called zero air, using a
calibration kit that includes a calibration cup, calibration gas, sample tubing, and a fixed flow
regulator with an on/off knob. RKI Instruments, Inc. recommends using a 0.5 LPM (liters per
minute) fixed flow regulator.
1. Remove the enclosure’s cover by unscrewing the four cover screws, one at each corner.
2. Set a voltmeter to measure in the millivolt (mV) range.
3. Plug the voltmeter leads into the test points on the amplifier PCB. Plug the positive lead
into the test point labeled
CAL+
; plug the negative lead into the test point labeled
CAL-
.
4. Screw the regulator into the zero air calibration cylinder.
5. Use the sample tubing to connect the regulator to the calibration cup.
6. Turn the regulator’s on/off knob counterclockwise to open it.
7. Hold the calibration cup against the H
2
S sensor’s face. Leave the rubber boot and sealing
spacer on the sensor when calibrating. Hold the cup on gently to allow gas to escape and
avoid pressurizing the sensor’s sensing face.
8. Allow the gas to flow for 2 minutes.
9. Verify a voltmeter reading of 100 mV (±2 mV).
10. If necessary, use a flat-blade screwdriver to adjust the zero pot until the voltmeter reading
is 100 mV (±2 mV).
11. Turn the regulator on/off knob clockwise to close it.
12. Remove the calibration cup from the sensor face.
13. Unscrew the regulator from the zero air calibration cylinder. For convenience, leave the
sample tubing connected to the regulator and the calibration cup.
14. Store the components of the calibration kit in a safe and convenient place.
15. Remove the voltmeter leads from the test points.
16. Secure the cover to the enclosure.
