Rockwell Automation 1715-OF8I Redundant I/O System User Manual - Manual (Page 221)

Rockwell Automation Publication 1715-UM001C-EN-P - March 2014 221
1715 Redundant I/O System in SIL 2 Safety Applications Chapter 6
The task period and task watchdog are configured in the Task Properties dialog
box.
Configuring the Output Module Program/Fault Actions
For a SIL 2 safety system, the user is responsible for making sure that the SIL 2
related safety code, including the SIL 2 Add-On Instructions, are being scanned
using a safety task watchdog.
See Using ControLogix in SIL 2 Safety Applications Reference Manual for safety
watchdog requirements.
Safety Watchdog
Configure the properties of the task used for safety correctly for your application.
• Priority: must be the highest-priority task in the application (lowest
number).
• Watchdog: the value entered for the SIL 2 safety task must be large enough
for all logic in the task to be scanned.
If the task execution time exceeds the watchdog time, a major fault occurs on the
controller. Users must monitor the watchdog and program the system outputs to
transition to the safe state (typically the OFF state) in the event of a major fault
occurring on the controller. For more information on faults see the Using
ControLogix in SIL 2 Safety Applications Reference Manual .
IMPORTANT You must dedicate a specific task for safety-related functions and set that task
to the highest priority (1). SIL 2 safety logic and logic intended for use in non-
SIL 2 functions must be separate.
IMPORTANT The preferred way to meet this controller requirement in a 1715 SIL 2 system is
to configure both the PROGRAM MODE and FAULT MODE tables for the
1715-OB8DE and 1715-OF8I with safe state values.