Model 580A
24
3.9 Check Points for Calibration and Operation
3.9.1 Frequency of Calibration
It is very important that the owner/operator of this equipment determine the correct
calibration schedule for their particular environment. The frequency of calibration may be
substantially shorter then 90 days depending on environmental contaminants and
conditions. This calibration frequency should follow a regular calibration routine and
procedure.
3.9.2 Background of Combustible Gases
In some applications, there is an occasional or continuous presence of “background”
combustible gases. Generally, this is a very small % LEL. Usually, it is advisable to zero
out the background gas concentration during calibration.
To Zero the Background Gas Concentration
1. Isolate the sensor from the surrounding air by placing your hand tightly over the
sensor.
2. Observe the reading on the “%” LEL display. A gradual drop in reading indicates
the presence of background or combustible gases. Keeping the hand over the
sensor, wait for the reading to stabilize and start the calibration without the
calibration cap.
3. When “
AC
” displays, remove your hand from 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 false alarms,
GMI 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 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 previous warning is applicable to all catalytic bead sensors.
