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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DANGER
In special cases (e.g., if two sensors are connected to two AC500
digital I/O channels from different I/O modules in parallel, etc.), dig-
ital standard I/O modules from AC500 platform can be also used in
functional safety applications up to PL d (ISO 13849-1) and SIL CL
2 (IEC 62061). However, more detailed functional safety application
analysis is required (contact AC500 technical support at
www.abb.com/PLC for more details), which is not shown in this doc-
ument.
To fulfill PL c (ISO 13849-1) requirements for input part, special DC measures shall be
implemented according to ISO 13849-1. The following measure was selected for the
input part:
- Cyclic test stimulus by dynamic change of the input signals, which provides DC
= 90% (see Annex E, ISO 13849-1)
The exemplary realization of this measure in AC500/AC500-S setup is presented in
Figure 5 and is based on some assumptions, which are later described in Chapter 3 in
details:
- Generation of dynamic pulses is done e.g., from non-safety PM5xx program but
the supervision of the test pulse pattern is done on SM560-S Safety CPU
o For data exchange between SM560-S and PM5xx two options can be
used:
§ SF_DPRAM_PM5XX_S_REC and
SF_DPRAM_PM5XX_S_SEND FBs from Safe-
tyExt_AC500_V22.lib [1] or
§ Cyclic Non-safe Data Exchange [2]
DANGER
50 Hz and 60 Hz frequencies shall be avoided for dynamic pulse
generation to avoid electrical noise interference.
- The safety reaction is triggered by SM560-S Safety CPU (in our example
through DX581-S digital safety input/output module), if the expected test pattern
is not available.
o Stuck-at-1 error are covered by the test pulse test
o Cross-talk between other channels can be implemented using time-
shifted (unique) dynamic test pulses for different input channels or differ-
ent test pulse frequencies
DANGER
Additional fault exclusion argumentation is required to exclude the
availability of similar periodic signals (with the same frequency as
that selected for dynamic test pulse generation on DC523 (see Fig-
ure 5)) within PM573 CPU.
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