Rockwell Automation Publication 1756-RM093J-EN-P - April 2018 39
Characteristics of Safety Tags, the Safety Task, and Safety Programs Chapter 5
For SIL 2-only safety, a safety task signature is not required. However, if any
SIL 3 safety functions are used within the safety task, a safety task signature is
required.
Safety-locking the safety task once testing is completed is recommended for SIL 2
applications. Locking the safety task enables additional security features. You may
also use FactoryTalk® Security
and RSLogix 5000 routine source protection to
limit access to safety-related logic.
For more information on generating a safety task signature and safety-locking the
safety task, refer to the GuardLogix Controllers User Manual, publication
1756-UM020
, or the Compact GuardLogix Controllers User Manual,
publication 1768-UM002
.
SIL 2 Safety Inputs
CompactBlock™ Guard I/O™ (1791-series), ArmorBlock®
Guard I/O™ (1732-
series), and POINT Guard I/O™ (1734-series) safety input modules support
single-channel SIL 2 safety input circuits. Because these modules are also rated
for SIL 3 operation, mixing SIL 2 and SIL 3 circuits on the same module is
allowed, provided you follow these guidelines.
These two wiring examples show how to wire SIL 2 safety circuits to Guard I/O
safety input modules. These examples make use of onboard test sources (T0…Tx)
that are resident on all 1791 and 1732 safety input modules.
Figure 11 - Input Wiring
Guard I/O modules group inputs in pairs to facilitate Cat 3, Cat 4, and SIL 3
safety functions. For use in Cat 1, Cat 2, and SIL 2 safety functions, module
inputs should still be used in pairs as illustrated. Two SIL 2 safety functions are
shown wired to inputs I0 and I1 using test sources T0 and T1, respectively.
Figure 12 - Input Wiring in Pairs
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