Detcon DM-700 - Manual (Page 20)

Model DM-700
DM-700 Instruction Manual Rev. 4.0 Page 16 of 48
3.4 Calibration Mode
3.4.1 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 613-120000-700 700 Series Splash Guard with integral Cal Port and Calibration Wind
Guard (P/N 943-000000-000) -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 1: 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 2: 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=AutoZero …PGM2=AutoSpan”. 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 4-20mA signal drops to 2mA and is held at this
level until the program returns to normal operation. Modbus™ Status Register bit 14 is also set
to signify when the sensor is in-calibration mode.
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.
3.4.2 AutoSpan