Rockwell Automation T8094 8000 Series TMR System Safety Manual - Manual (Page 57)

SAFETY MANUAL
D oc N umber T8094
I ssue 27 – June 2013
Page 36 of 103
3.8 INPUT AND OUTPUT FORCING
Locking and forcing of individual inputs and outputs from the IEC1131 Workbench are
supported for engineering, installation and commissioning purposes. In-service,
maintenance overrides for safety-related inputs and outputs should be implemented
using the application program. The IEC1131 Workbench initiated locking and forcing
requires:
• The TMR Processor keyswitch to be in the “Maintain“ position to make
changes to the lock or force status of any point
• Access to the Workbench lock & write commands, which are multi-level
password protected.
• A list of the currently locked points are read back from the TMR system and
made available within the IEC1131 Workbench
The TMR Processor inhibit LED will indicate when one or more I/O points are locked.
The application program can determine how many points are currently locked by used
the information available from the TMR Processor complex equipment; it is highly
recommended that this be used to control additional status display and/or for logging
purposes.
All input and output locks (and forces) can be removed using either a single
function from the IEC1131 Workbench or from an edge triggered signal to the
TMR Processor board within the application program. If locking is used, a
safety-related input connected to an operator accessible switch shall be
implemented to initiate the removal of the lock and force conditions.
It is important that the effects of forcing input and output points on the process and
their safety impact are understood by any person using these facilities.
The system will allow the forced conditions to be maintained during normal operation.
When returning to normal operation it is recommended that all locked and
forced points be returned to normal operation. It is the plant operators’
responsibility to ensure that if forced conditions are present that they do not jeopardise
the functional safety.