Detcon FP-624D - Manual (Page 32)

Model FP-624D
FP-624D Instruction Manual Rev. 1.2 Page 28 of 42
3.6.2 Fault Diagnostic/Failsafe Features
Fail-Safe/Fault Supervision
Model FP-624D MicroSafe™ sensors are designed for Fail-Safe operation. If any of the diagnostic faults
listed below are active, the sensor display will scroll the message “Fault Detected” every 60 seconds 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. The “Global Fault” bit in the Modbus fault register is also set and the fault
relay output is activated. These include the AutoZero and AutoSpan Calibration faults, Sensor Faults,
Processor Fault, Memory Fault, Loop Fault, and Input Voltage Fault. (The 0mA fault level is not employed
for a Temperature Fault, or during Calibration.)
NOTE: Refer to the Troubleshooting Guide, Section 6, for guidance on fault conditions.
Zero Fault
If the sensor drifts below –10% LEL, the “Zero Fault” will be declared. A “Zero Fault” will cause a “Fault
Detected” message to scroll once a minute on the transmitter display and drop the 4-20mA output to 0mA.
The “Zero Fault” bit in the Modbus fault register will be set. The sensor should be considered “Out-of-
Service” until a successful AutoZero calibration is performed.
Range Fault – AutoSpan
If the sensor fails the minimum signal change criteria during AutoSpan sequence (Section 3.4), the “Range
Fault” will be declared. A “Range Fault” will cause a “Fault Detected” message to scroll once a minute on the
sensor display and drop the 4-20mA output to 0mA. The “Range Fault” bit in the Modbus fault register will
be set. 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 during AutoSpan sequence (Section 3.4), the “Stability Fault” will
be declared. A “Stability Fault” will cause a “Fault Detected” message to scroll once a minute on the sensor
display and drop the mA output to 0mA. The “Stability Fault” bit in the Modbus fault register will be set. The
sensor should be considered as “Out-of-Service” until a successful AutoSpan calibration is performed.
Clearing Fault - AutoSpan
If the sensor fails the signal stability criteria during AutoSpan sequence (Section 3.4), the “Clearing Fault” will
be declared. A “Clearing Fault” will cause a “Fault Detected” message to scroll once a minute on the sensor
display and drop the mA output to 0mA. The “Clearing Fault” bit in the Modbus fault register will be set. The
sensor should be considered as “Out-of-Service” until a successful AutoSpan calibration is performed.
Sensor Current Fault
If the current through the sensor bridge (See Figure 3) drifts outside the range of 200mA ± 50mA, a “Sensor
Current Fault” will be declared. A “Sensor Current Fault” will cause a “Fault Detected” message to scroll
once a minute on the transmitter display. If a Sensor Current Fault occurs, the 4-20mA signal will be set at
0mA and the “Sensor Current Fault” bit will be set until the fault condition is resolved.
Sensor Voltage Fault