Siemens SIRIUS 3SK1

Safety systems - General information
4.3 Basic terminology
3SK1 safety relays
Manual, 04/2013, A5E02526190021A/RS-AA/01
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4.3 Basic terminology
4.3.1 Redundancy/single-channel and two-channel
Redundancy
With redundancy, more than one component is implemented for the same function, so a
faulty function of a component is performed instead by the other component(s).
A redundant configuration reduces the probability of a function failing due to a single
defective component. This requirement is essential for achieving SILCL 3 in accordance with
IEC 62061, SIL 3 in accordance with IEC 61508 and PL e (Cat. 4) in accordance with
ISO 13849-1 (also necessary for SIL 2 / PL d under certain circumstances).
The simplest form of redundancy is two-channel redundancy.
If a circuit fails, two-channel redundancy ensures that the safety function is maintained.
In a redundant system configuration, the subsystems for detecting and reacting must also be
implemented with two-channel redundancy.
Note
All SIRIUS Safety devices that comply with SILCL 3 in accordance with IEC 62061, SIL 3 in
accordance with IEC 61508 and PL e (Cat. 4) in accordance with DIN EN ISO 13849-1 are
redundantly configured with regard to the internal logic as well as with regard to the output
circuits.
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Figure 4-1 Single-channel sensor connection