G
ENERAL
M
ONITORS
26776 Simpatica Circle • Lake Forest, CA 92630 • +1-949-581-4464 • Fax +1-949-581-1151
www.generalmonitors.com • email: [email protected]
C
ALIBRATION
P
ROCEDURE
1. If the gas alarm relays are not to be activated during calibration (since they might be connected to
external devices), move the recessed front panel rocker switch to the "CAL" position. The MALF light
will flash and the relays will be held in standby. The % LEL display and gas alarm LED's will function
normally.
2. Locate the ZERO and SPAN potentiometer screwdriver access openings for each channel on the front
panel.
3. Select one channel to calibrate. Assure that the sensing assembly for that channel is in "clean" air.
4. Adjust the appropriate (20 turn) ZERO pot for that channel until the % LEL display reads zero, using a
small thin-blade screwdriver. Make sure that you are adjusting the proper channel zero setting by
observing the channel % LEL display.
5. Expose the sensor for the channel being calibrated to calibration gas, using the GMI portable purge
calibrator (for methane, hydrogen, etc.), P/N 1400150, or calibration chamber, P/N 1400200 (for
solvents).
6. Adjust the channel's SPAN pot to bring the % LEL display to the concentration matching the calibration
gas being used. Note: gas cylinders are normally labeled either in % LEL or % by volume of the gas.
Refer to NFPA Standards No. 325M or other authority for conversions if required. For methane, 50%
LEL = 2.5% gas by volume; for hydrogen, 50% LEL = 2.0% gas by volume.
7.
Remove the calibration gas, allowing the sensor to return to clean air. Allow sufficient time for the meter
reading to stabilize. It should stabilize at or near 0% LEL. If a minor adjustment is required to reach
zero, the calibration is acceptable. Adjust the meter to zero with the ZERO potentiometer. If a
significant adjustment is necessary to return to zero, repeat the entire calibration procedure.
8.
Repeat the previous steps (1-7) for the other channel.
