Rockwell Automation 8000 Series TMR System - Manual (Page 15)

OPERATOR AND MAINTENANCE MANUAL
D o c N u m b e r 5 5 2 8 6 4
I s s u e 0 2 J u n e 2 0 0 4 P a g e 5 o f 2 3
1.9 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 using 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.