Rockwell Automation T8444 Trusted TMR Pulse Generator and Monitoring Module - Manual (Page 32)

Trusted
TM
Module T8444
Issue 09 Apr 10 PD-T8444 32
5. Fault Finding and Maintenance
5.1. Fault Reporting
Module faults are reported to the user through visual indicators on the front panel of the module and
through status variables which may be automatically monitored in the application programs and
external system communications interfaces. There are generally two types of faults that must be
remedied by the user: external wiring and module faults. External wiring faults require corrective action
in the field to repair the fault condition. Module faults require replacement of the module.
5.2. Field Wiring Faults
By measuring the channel voltage and current, the module automatically detects field-wiring and load
faults. When a field signal fails open circuit, short circuit or there is no field supply voltage connected,
the status indicator will display the configured LED mode and the line fault status for that channel will
be set to ‘1’. All other channels will be unaffected, except in the case of common cause wiring and
supply voltage faults in the field.
The field voltage and current variables can be monitored to determine the actual operating conditions
of each channel. This additional information assists the user in determining the specific type of wiring
fault.
Once the specific field-wiring fault has been identified and corrected, the status variables and status
indicator will display the normal on/off status of the field device.
5.3. Module Faults
Extensive diagnostics provide the automatic detection of module faults. The TMR architecture of the
module and the diagnostics performed ensure the validity of all critical circuits. Using the TMR
architecture provides a Fault Tolerant method to withstand the first fault occurrence on the module and
continue normal control without interruption in the system or process. Faults are reported to the user
through the Healthy status indicators on the front panel of the module and through the INFO and
HKEEPING variables. Under normal operations all three Healthy Indicators are green. When a fault
occurs, one of the Healthy Indicators will be flashing red. It is recommended that this condition is
investigated and if the fault is within the module, it should be replaced .