MSA 610A - Calibration Checks and Options; Calibration Frequency; Background Gas Handling; Sensor Replacement

MODEL 610A
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3.9 Check Points for Calibration and Operation
3.9.1 Frequency of Calibration
GMI recommends that the calibration be checked on each sensor at least every ninety
(90) days. If a sensor is installed where it may be subjected to splashing wat er, m ud o r
dirt accumulation, or adverse gases, more frequent calibrat i on is rec omm ended. The
exact f requency can vary with the severity of conditions and must be established in t he
field.
3.9.2 Background of Combustible Gases
In some applications, there is an occasional or continuous p resence of “b ackground”
combustible gases. Generally, this is a very small % LEL. Usually, it is advisable t o zero
out the background gas concentration during calibration.
To Zero the Background Gas Concentration:
1. Isolate the sensor from the surrounding air by placi ng your hand t ight ly over t he
sensor.
2. Observe the reading on the “%” LEL display. A gradual drop in reading indicates t he
presence of background or combustible gases. Keeping the hand over t he s ensor,
wait f or the reading to stabilize and start the calibration without the calibration cap.
3. When “AC” displays, remove your hand f rom the sensor, place the cap over the
sensor and continue the calibration.
3.9.3 Replacing a Sensor
When a sensor is replaced, the new sensor must be calibrated. To avoid f alse alarms,
General Monitors recommends disabling all the alarm circuits until the sensor is
calibrated. For better results, the sensor should be powered up at least one hour before
calibration.
CAUTION: Extended exposure of a sensor to a high concent ration of c ombust ibl e
gases can introduce stress in the sensing element, which m ay s eriousl y
af f ect performance. Re-calibration should therefore be performed af ter 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 of f s cale,
may mean an explosive concentration of gas is present.
NOTE: The previous warning is applicable to all catalytic bead sensors.
3.10 Special Options
3.10.1 Optional Model 610A Controller for Zone Control (Voting)
The Model 610A Controller can be supplied with a special voting option, when s pecif ied
on the original order for the equipment. A system supplied for voting use, must be the
common relay version and will require that two channels reach the High alarm set point