With the publication of Edition 3 of the harmonized EN 61496-1 standard it is no longer
possible to use a Type 2 safety light barrier for safety functions assessed as
SIL 2 / PL d.
If a safety level of SIL 2 / PL d (or higher) is required and it is nevertheless intended to
use a safety light barrier, then it will be necessary to use a Type 4 safety light barrier.
This regulatory requirement derives from the fact that the reduction of risk that can be
obtained via a photoelectric safety barrier is not only a function of the safety level of its
electronic parts, but is also determined by its systematic capabilities (for example:
environmental influences, EMC, optical performance and detection principle).
The systematic capability of a Type 2 photoelectric barrier may in fact not be sufficient
to ensure adequate risk reduction for SIL 2 / PL d applications.
The standard also establishes that the labelling of Type 2 safety barriers must indicate
such limitation to SIL 1 / PL c.
The PFHd values declared for the electronic control part of the device, on the other
hand, are not limited and therefore it is possible to use the PFHd value provided by the
manufacturer of the device in the global assessment of the safety function, even if it
exceeds the SIL 1 / PLc range.
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