Rockwell Automation T8402 Trusted Dual 24V dc Digital Input Module - 60 Channel - Manual (Page 25)

Trusted
TM
Module T8402
Issue 13 April 10 PD-T8402 25
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.
5.2. Field Wiring 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 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.
Once the field-wiring fault has been identified and corrected, the input status 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 1-oo-2D Dual architecture
of the input module and the diagnostics performed ensure the validity of all critical circuits. Using the
1-oo-2D Dual 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 cause 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
or with a SmartSlot for a spare replacement module.