Rockwell Automation T8442 Trusted TMR Speed Monitor - Manual (Page 56)

Trusted
TM
Module T8442
Issue 8 Apr 10 PD-T8442 56
5. Fault Finding and Maintenance
5.1. Fault Reporting
Input module faults are reported to the user through visual indicators (LEDs) on the front panel of the
module. Faults are also reported via 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 input module.
The module monitors the speed input to determine if they are within the appropriate parameters.
5.2. Field Faults
The input circuits of the module may be used to detect field wiring faults in addition to alarm states. To
achieve this, line monitoring components must be fitted to the field device.
By comparing the input signal from the field with pre-configured alarm thresholds, the module can
automatically detect field-wiring faults. When a field signal fails open or short-circuit, or to an
intermediate value, the input channel status LED will flash red (default setting). The corresponding
input state will be reported and the line fault status for that channel will be set to ‘1’. All other input
channels will be unaffected, except in the case of common cause wiring faults in the field.
NOTE: A loss of a speed input is a safety critical fault. Once the field fault has been identified and
corrected, the processor RESET button must be pressed to clear the fault indication and then the input
status and the input status LED will display the normal on/off status of the field device and field wiring.
5.3. Module Faults
Extensive diagnostics provide the automatic detection of module faults. The TMR architecture of the
input 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 input measurements without interruption in the system or process. Faults are
reported to the user through the Healthy status LEDs on the front panel of the module and through the
INFO and HKEEPING variables. Under normal operations all three Healthy LEDs are green. When a
fault occurs, one of the Healthy LEDs will flash red. It is recommended that this condition is
investigated, and if the fault is within the module, it should be replaced.
Module replacement activities depend on the type of spare module configuration chosen when the
system was configured and installed. The module may be configured with a dedicated Companion Slot
for a spare replacement module. SmartSlot operation is not available. Refer to Operator and
Maintenance Manual for module replacement procedure.