Model CXT-DM
CXT-DM Instruction Manual
Rev. 2.0
Page 21 of 54
To enter Calibration Mode hold the magnet over PGM1 for 3 seconds. If the sensor is experiencing a fault
condition the “
” prompt will not appear until the fault(s) have been displayed. When the ITM enters
Calibration Mode the display will scroll “
Pgm1=Zero . . . Pgm2=Span
” twice before returning to Normal
Mode (about 5 seconds).
3.3.1
AutoZero
The AutoZero function is used to zero the sensor. AutoZero should be performed periodically or as required.
AutoZero should be considered after periods of over-range target gas exposure. Local ambient air can be used
to zero calibrate a toxic gas sensor as long as it can be confirmed that it contains no target or interference
gasses. If this cannot be confirmed then a zero air or N
2
cylinder should be used. Pure N
2
must be used for
zero calibration of the O
2
deficiency sensors.
Material Requirements:
•
-Detcon PN 327-000000-000 MicroSafe™ Programming Magnet
•
-Detcon PN 613-120000-700 Splash Guard with integral Cal Port and with Wind Guard. -OR-
•
-Detcon PN 943-000006-132 Threaded Calibration Adapter
•
-Detcon PN 942-001123-000 Zero Air cal gas (or use ambient air if no target gas is present).
•
-Detcon P/N 942-640023-100 Nitrogen 99.99%
NOTE:
The zero gas source may be zero air or N
2
for toxic sensors, but must be pure N
2
(99.99%) for O
2
deficiency sensors
NOTE
: The Calibration Wind Guard must be used when the Splashguard Adapter with
integral Cal Port is used. Failure to use the Calibration Wind Guard may result in an inaccurate
AutoZero calibration.
a)
For toxic sensors, if the ambient air is known to contain no target gas content, then it can be used for zero
calibration. If a zero gas cal cylinder is going to be used, attach the calibration adapter and set flow rate of
200-500cc/min (500cc/min is the recommended flow rate) and let sensor purge for 1-2 minutes before
executing the AutoZero. For O
2
deficiency sensors, apply N
2
at a set flow rate of 500cc/min for 3-5
minutes before executing AutoZero.
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
PGM1 for 3 seconds once the “
” prompt appears to execute AutoZero (or allow to timeout in 5 seconds if
AutoZero is not desired).
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)
The ITM will display the following sequence of text messages as it proceeds through the AutoZero
sequence:
Zero Cal . . . Setting Zero . . . Zero Saved (each will scroll twice)
d)
Remove the zero gas and calibration adapter, if applicable.