Detcon DM-700 - Manual (Page 28)

Model DM-700
DM-700 Instruction Manual Rev. 4.0 Page 24 of 48
In-Calibration Status
When the sensor is engaged in AutoZero or AutoSpan calibrations, the 4-20 mA output signal is taken to 2.0
mA and the in-calibration Modbus™ Status Register bit 14 is set. This alerts the user that the ITM is not in an
active measurement mode. This feature also allows the user to log the AutoZero and AutoSpan events via
their master control system.
Sensor Life
Sensor Life is calculated after each AutoSpan calibration and is reported as an indicator of remaining service
life. It is reported in the “View Sensor Status” menu and as a RS-485 Modbus™ register bit. Sensor Life is
reported on a scale of 0-100%. When Sensor Life falls below 25%, the sensor cell should be replaced within a
reasonable maintenance schedule.
Last AutoSpan Date
This reports the number of days that have elapsed since the last successful AutoSpan. This is reported in the
View Sensor Status menu. After 180 days, an AutoSpan Fault will be declared.
3.6.2 Fault Diagnostic/Failsafe Features
Fail-Safe/Fault Supervision
Model DM-700 sensors are designed for Fail-Safe operation. If any of the diagnostic faults listed below are
active, the ITM Display will scroll the message “Fault Detected” every 1 minute during normal operation. At
any time during “Fault Detected” mode, holding the programming magnet over PGM1 or PGM2 for 1 second
will display the active fault(s). All active faults are reported sequentially.
Most fault conditions result in failed operation of the sensor. In these cases the 4-20mA signal is dropped to
the universal fault level of 0mA. These include the AutoSpan Calibration faults, Heater Fault, Sensor Fault,
Processor Fault, Memory Fault, Loop Fault, and Input Voltage Fault. The 0mA fault level is not employed for
Temperature or AutoSpan Faults. For every diagnostic fault condition the associated RS-485 Modbus™ fault
register will be flagged to alert the user digitally.
NOTE: Refer to the Troubleshooting Guide section for guidance on how to address fault
conditions.
Range Fault – AutoSpan
If the sensor fails the minimum signal change criteria (Section 3.4.2) during AutoSpan sequence, the “Range
Fault” will be declared. A “Range Fault” will cause a “Fault Detected” message to flash intermittently on the
ITM display and drop the 4-20mA output to 0mA. The Modbus™ fault register bit for Range Fault will be set
and will not clear until the fault condition has been cleared. The sensor should be considered ‘Out-of-Service’
until a successful AutoSpan calibration is performed.
Stability Fault - AutoSpan
If the sensor fails the signal stability criteria (Section 3.4.2) during AutoSpan sequence, the “Stability Fault”
will be declared. A “Stability Fault” will cause a “Fault Detected” message to flash intermittently on the ITM
display and drop the mA output to 0 mA. The Modbus™ fault register bit for Stability Fault will be set and
will not clear until the fault condition has been cleared. The sensor should be considered as ‘Out-of-Service’
until a successful AutoSpan calibration is performed.