S4000C
19
General Monitors recommends that a calibration schedule be established and followed. A
logbook should also be kept, showing calibration dates and dates of sensor replacement.
4.6.1 Calibration
Procedure
If it is suspected that gases are present, it will be necessary to purge the sensor environment
with Zero Air. If Zero Air is not available, cover the sensor for about thirty seconds before
applying the calibration gas. Zero Air is air that is hydrocarbon free.
Entering Calibration Mode automatically disables the alarm circuits by sending a 1.5mA output
signal and disabling the Warn and Alarm relays, if present. This will also prevent activation of
the remote relay contacts when using a General Monitors Readout/Relay Display Module with
the Model S4000C.
To enter Calibration Mode, place the magnet over the GM Logo on the cover of the unit (Figure
4) and hold it there until “
AC
” (Figure 13) appears on the display (about ten seconds). The
display will flash the remaining sensor life (Section 4.6.4) for about ten seconds, while the unit
acquires the zero reading. Ensure that the sensor is seeing clean air during this time.
Figure 13: Automatic Calibration Mode
Apply the calibration gas concentration to the sensor (usually 50% LEL of the desired gas). The
display will change from “
AC
” (Automatic Calibration) to “
CP
” (Calibration in Progress),
indicating that the sensor is responding to the calibration gas (Figure 14).
Figure 14: Calibration In Progress Mode
After one or two minutes, the display will change from “
CP
” to “
CC
” (Figure 15), indicating that
the calibration is complete.
Figure 15: Calibration Complete Mode
Remove the gas and wait for the unit to return to normal operation. The display will indicate a
few percent full-scale and then drop to “
0
”.
