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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Key requirements for Category 2 (ISO 13849-1) are:
- Requirements of system B (refer to ISO 13849-1 for details) and the use of well-
tried safety principles shall apply
- Safety function shall be checked at suitable intervals by the machine control
system
- The occurrence of a fault can lead to the loss of the safety function between the
checks
- The loss of safety function is detected by the check
Category 2 architecture realization using AC500/AC500-S modules (see Figure 1) is
shown in Figure 4.
Figure 4. Category 2 equivalent architecture using AC500/AC500-S modules
As one can see from Figure 4, safety logic processing and safety output part are fully
covered by SM560-S Safety CPU (SIL3, PL e) and DX581-S digital safety input/output
module, which even significantly exceed the requirements from PL c (ISO 13849-1).
Nevertheless, we need an additional analysis for the input part in which standard (non-
safety) AC500 modules (DC523 and PM573) are used. This input part will be always
application-specific and will require additional measures to satisfy PL c requirements.
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