Detcon DM-700 - Manual (Page 22)

Model DM-700
DM-700 Instruction Manual Rev. 4.0 Page 18 of 48
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) 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 2½ 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” and will not clear the fault until a successful AutoSpan is completed.
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.
For about 1 minute the reading will auto-adjust to the programmed AutoSpan level. For about another 30
seconds, the AutoSpan sequence checks the sensor for acceptable reading stability. If the sensor fails the
stability check, the reading is re-adjusted back to the AutoSpan level and the cycle repeats until the stability
check is passed. Up to three additional 30-second stability check periods are allowed before the unit reports a
“Stability Fault” twice and the ITM will return to normal operation, aborting the AutoSpan sequence. The
ITM will continue to report a “Stability Fault” and will not clear the fault until a successful AutoSpan is
completed.
If the sensor passes the stability check, the ITM reports a series of messages:
“Span OK”
“Sensor Life XXX%”
“Remove Span 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 5% of range, the ITM will display “Span Complete” and will revert
to normal operation. If the sensor fails to clear to less than 5% 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” and will not clear the fault until a successful AutoSpan is
completed.
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) The AutoSpan calibration is complete.
NOTE 1: If the sensor fails the minimum signal change criteria, a “Range Fault” will be
declared and a “Fault Detected” message will be displayed alternately with the sensor’s
current reading. The 4-20mA output will be taken to 0mA and the ‘Range Fault’ fault bit will
be set on the Modbus™ output.
NOTE 2: If the sensor fails the stability criteria, a “Stability Fault” will be declared and a
“Fault Detected” message will be displayed alternately with the sensor’s current reading. The
4-20mA output will be taken to 0mA and the ‘Stability Fault’ fault bit will be set on the
Modbus™ output.
NOTE 3: If the sensor fails the clearing time criteria, a “Clearing Fault” will be declared and a
“Fault Detected” message will be displayed alternately with the sensor’s current reading. The