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6. CALIBRATION
6.0. General
Calibration of the monitor is required by law to be performed every 30 days to allow
the monitor electronics to compensate for any aging of the sensor cell. The process
consists of applying
ZERO
and
SPAN
gases to the sensor cell and holding a magnet
to the TEST/CALIBRATE magnetic switch to allow the electronics to save the two
values.
6.1. Zero Calibration
1) Apply a ZERO gas to the sensor cell input and wait 2 minutes for the cell to
stabalize.
2) Hold a magnet to the magnetically activated CAL/TEST switch
3) Observe the LCD display and verify the value jumps to 2 or 3 PPM and then
slowly decreases to ZERO. When the display reaches ZERO also observe that the
display now blinks ZERO. This indicates the ZERO parameters for the sensor cell
have been saved in memory. It also starts a timer that gives the operator 3 minutes to
properly perform the SPAN calibration.
4) Remove the magnet from the CAL/TEST switch
5) During ZERO calibration of the sensor electronics, the unit evaluates the amplified
gas sensor cell output and the sensor electronics ZERO adjust to determine that the
amplified cell output value is between 0.10 VDC and 0.50 VDC at the test point TP1.
If the voltage is not between these two values a
sensor calibration error “E”
will
appear in the left digit of the LCD display as the LCD begins to flash
“E00”
. The
“
E”
error indication will remain
ON
until the ZERO is adjusted and the sensor is
re-calibrated. The PLC Monitor System Master Station will also be notified that a
calibration error has occurred at this sensor. Should the
“E”
error indication occur,
open the sensor enclosure door and connect a VOM between TP1 and POWER
RETURN (J1-3). Adjust the ZERO ADJUST potentionmeter until the VOM
indicates 0.30 VDC. Perform the ZERO calibration again.
6) Remove the ZERO gas from the sensor cell and prepare to perform the SPAN
calibration.