Model CXT-IR
CXT-IR Instruction Manual
Rev. 2.1
Page 21 of 48
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 combustible 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.
Material Requirements:
•
DetconMicroSafe™ Programming Magnet (PN 327-000000-000)
•
Detcon Splash Guard with integral Cal Port (PN 613-120000-700) and Calibration Wind Guard (PN
613-120000-700) -OR-
•
Detcon Threaded Calibration Adapter (PN 943-000006-132)
•
Detcon Zero Air cal gas (PN 942-001123-000) (or use ambient air if no target gas is present)
•
Detcon Nitrogen 99.99% (PN 942-640023-100)
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 combustible gas 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 to 2 minutes
before executing the
AutoZero
.
b)
From normal operation, enter calibration mode by holding the programming magnet over
PGM1
for 3
seconds 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:
The "
◄
" prompt will show that the magnetic switch is activated during the 3 second
hold period.
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.
3.3.2
AutoSpan
The AutoSpan function is used to span calibrate the sensor. AutoSpan should be performed periodically or as
required. AutoSpan should be considered after periods of over-range target gas exposure. Unless otherwise
specified, span adjustment is recommended at 50% of range. This function is called
AUTO SPAN
.
