35-3001A-01-XX1 Sample-Draw Detector Operator’s Manual • 19
Setting the Zero Reading
CAUTION:
If you suspect the presence of combustible gas in the monitoring environment,
use the calibration kit and the zero air calibration cylinder to introduce “fresh
air” to the sensor and verify an accurate zero setting. See “Calibration” on
page 26 for instructions on using a zero air calibration cylinder for setting the
zero reading.
1. Verify that the sample-draw detector is sampling a fresh air environment (environment
known to be free of combustible gas).
2. Open the housing door.
3. Set a voltmeter to measure in the millivolt (mV) range.
4. 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.
5. Verify a voltmeter reading of 100 mV (± 2 mV).
6. If necessary, use a small flat-blade screwdriver to adjust the zero potentiometer until the
voltmeter reading is 100 mV (± 2 mV).
7. Remove the voltmeter leads from the test points.
8. Close the housing door.
Low Flow Contact Operation
The low flow contact is closed during normal operation and opens during a low flow
condition or if the sample-draw detector loses power.
Monitoring of the low flow contacts can be done with a contact monitoring device that
does not exceed the relay ratings below. Alternatively, the contacts could be used to power
a device that does not exceed the relay contact ratings below. The ratings are for a resistive
load.
Table 2: Low Flow Relay Specifications
Voltage
Amps
125 VAC
0.6 A
30 VDC
1 A
110 VDC
0.6 A
