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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]
Model 610 Calibration Info
Calibration to customer specified gas is initially done at the factory. We recommend that the Model 610
system be re-calibrated upon start-up, and that calibration be checked at least every 90 days thereafter.
B
ACKGROUND OF
C
OMBUSTIBLE
G
ASES
In some applications there will be an occasional or continuous presence of "background" combustible gases.
Generally this will be a very small % LEL. Usually it is advisable to zero out the background gas
concentration during calibration. To do so, isolate the sensor from the surrounding air using a plastic bag (or
by placing your hand tightly over the sensor). Observe the reading on the % LEL meter. A gradual drop in
reading indicates the presence of a background of combustible gases. With the bag in place, set the meter
to read 0% LEL using the ZERO potentiometer. Remove the bag and proceed with normal calibration.
CAUTION - E
XTENDED
E
XPOSURE TO
C
OMBUSTIBLE
G
ASES
Extended exposure of a sensor to a high concentration of combustible gases can introduce stress in the
sensing element which may seriously affect performance. Re-calibration should therefore be performed after
an alarm due to a high concentration of gas, and the sensor should be replaced if necessary. A display
reading of 99% LEL, or high off-scale, may mean an explosive concentration of gas is present.
Note: the foregoing warning is applicable to all catalytic bead sensors regardless of manufacturer.
F
REQUENCY OF
C
ALIBRATION
As a rule of thumb, GMI recommends that the calibration be checked on each sensor at least every 90 days.
If a sensor is installed where it may be subjected to splashing water, mud or dirt accumulation, or adverse
gases, more frequent calibration is recommended. The exact frequency can vary with the severity of
conditions and must be established in the field.
C
ALIBRATION
C
HECK
-P
OINTS
a. A horizontal, one digit display (-), when the sensor is exposed to calibration gas, indicates the white and
black sensor leads are reversed. This same display will appear if the ZERO pot is adjusted below the
0% LEL setting (no gas at the sensor).
b. The SPAN potentiometer is a 20-turn pot. The number of clockwise turns required to obtain the correct
meter reading during calibration varies from one gas to another. For a particular gas at a specific
concentration, a steady increase over a short period of time in the number of turns required to obtain the
correct meter reading indicates that the sensor is losing sensitivity and/or has been contaminated.
Operators should periodically check how many turns remain in the span pot. GMI highly recommends
replacing the sensor while a few turns remain, since it is probably approaching the end of its useful life.
See Section V of the Instruction Manual for additional information.
