Detcon CXT-DM - Manual (Page 25)

Model CXT-DM
a) Verify that the AutoSpan Level is equal to the Calibration Span Gas Concentration. (Refer to View
Sensor Status in Section 3.4.1.) If the AutoSpan Level is not equal to the Calibration span gas
concentration, adjust the AutoSpan Level as instructed in Section 3.3.2 AutoSpan.
b) From Normal Operation, enter Calibration Mode by holding the programming magnet over PGM1 for 3
seconds. Note, the “ ” prompt will show that the magnetic switch is activated during the 3 second hold
period. The display will then scroll “PGM1=Zero PGM2=Span”. Hold the programming magnet over
PGM2 for 3 seconds to execute AutoSpan (or allow to timeout in 5 seconds if AutoSpan is not intended).
The ITM will then scroll “Apply XX ppm Gas”.
NOTE: Upon entering Calibration Mode, the Modbus™ Status Register bit 14 is set to signify
the sensor is in-calibration mode. This bit will remain set until the program returns to normal
operation.
c) Apply the span calibration test gas for toxic gas sensors at a flow rate of 200-500cc/min (500cc/min is the
recommended flow rate). As the sensor signal begins to increase the display will switch to flashing “XX“
reading as the ITM shows the sensor’s “as found” response to the span gas presented. If it fails to meet the
minimum in-range signal change criteria within 2 minutes, the display will report “Range Fault” twice
and the ITM will return to normal operation, aborting the AutoSpan sequence. The ITM will continue to
report a “Range Fault” for 1 minute.
NOTE: Ambient air should be used to calibrate O
2
deficiency sensors as long as the oxygen
concentration is confirmed to be 20.9%. There is no need to apply a flow of gas.
Assuming acceptable sensor signal change, after 1 minute the reading will auto-adjust to the programmed
AutoSpan level. The ITM then reports the following messages:
“Remove Gas”
d) Remove the span gas source and calibration adapter. The ITM will report a live reading as it clears toward
“0”. When the reading clears below 10% of range, the ITM will display “Span Complete” and will revert
to normal operation. If the sensor fails to clear to less than 10% in less than 5 minutes, a “Clearing Fault”
will be reported twice and the ITM will return to normal operation, aborting the AutoSpan sequence. The
ITM will continue to report a “Clearing Fault” for 1 minute.
NOTE: When calibrating O2 deficiency sensors, there is no requirement to clear to <5% of
range. The sensor will return to normal operation immediately after span adjustment.
e) AutoSpan calibration is complete.
NOTE 1: If the sensor fails the minimum signal change criteria, a “Range Fault” will be
declared and the ‘Range Fault’ fault bit will be set on the Modbus™ output.
NOTE 2: If the sensor fails the clearing time criteria, a “Clearing Fault” will be declared and
the ‘Clearing Fault’ fault bit will be set on the Modbus™ output.
CXT-DM Instruction Manual Rev. 1.6 Page 21 of 52