Rockwell Automation Publication 1756-RM093J-EN-P - April 2018
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Characteristics of Safety Tags, the Safety Task, and Safety Programs
Chapter 5
SIL 2 Safety Control in Standard Tasks (1756 GuardLogix controllers
only)
Because of the quality and amount of diagnostics built into the 1756
ControlLogix series of controllers, you can perform SIL 2 safety functions from
within standard tasks. This is also true for 1756 GuardLogix controllers.
To perform SIL 2 safety control within a GuardLogix standard task, you must
abide by requirements defined in the Using ControlLogix in SIL 2 Applications
Safety Reference Manual, publication
SIL 3 Safety–the Safety Task
Creation of a GuardLogix project automatically creates a single safety task. The
safety task has these additional characteristics:
•
GuardLogix controllers are the only controllers that support the safety
task.
•
The safety task cannot be deleted.
•
GuardLogix controllers support a single safety task.
•
Within the safety task, you can use multiple safety programs composed of
multiple safety routines.
•
You cannot schedule or execute standard routines from within the safety
task.
The safety task is a periodic timed task with a user-selectable task priority and
watchdog. In most cases, it is the controller’s top priority and the user-defined
program watchdog must be set to accommodate fluctuations in the execution of
the safety task.
Safety Task Limitations
You specify both the safety task period and the safety task watchdog. The safety
task period is the period at which the safety task executes. The safety task
watchdog is the maximum time allowed from the start of safety task scheduled
execution to its completion.
For more information on the safety task watchdog, see
,
IMPORTANT
You may not use the standard task in a 1768 Compact GuardLogix controller
for SIL-2 safety applications.
