Application Note for “Usage of AC500 digital standard I/Os in functional safety applications up to PL c (ISO 13849-1)”, V1.0.0
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2.2 Task
We want to show and describe an approach how AC500 digital standard I/O channels
can be used for functional safety applications up to PL c (ISO 13849-1) in combination
with SM560-S Safety CPU.
NOTICE
It is always highly recommended to use digital safety input channels
even for functional safety applications up to PL c (ISO 13849-1).
Thus, the presented approach with the usage of digital standard I/O
channels is only an option if spare digital standard I/O channels are
available and their reuse for functional safety functions up to PL c
is needed to satisfy specific customer requirements (e.g., limited
space in the control cabinet to add additional digital safety I/O mod-
ule, cost saving, etc.).
Customer benefits from using spare AC500 digital standard I/O channels for functional
safety applications up to PL c (ISO 13849-1) are:
- Smaller control cabinet dimensions are possible
- Cost savings on additional Safety I/O modules.
2.3 Solution
The proposed solution is based on the design analysis and additional diagnostic safety
measures which can be implemented using AC500/AC500-S setup shown in Figure 1
to enable usage of AC500 digital standard I/O channels in functional safety applica-
tions up to PL c (ISO 13849-1).
Figure 2 shows an overview on reachable Performance Levels depending on Cate-
gory, DCavg and MTTFd values, as defined in ISO 13849-1. As one can see from
Figure 2 (see a selection in blue), one of the most attractive approaches to satisfy PL
c (MTTFd = High or Medium) and even PL d (MTTFd = High) requirements is the usage
of Category 2, DCavg = Low.
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