Siemens SIRIUS 3RK3 - What Is Safety; Basic Terminology; Redundancy;Single-Channel and Two-Channel

3.7.2 What is safety?
Safety de󹪝nes a state in which the risk of damage is reduced to a tolerable level, or which can be
regarded as risk-free. Following on from this de󹪝nition, functional safety concerns persons,
machines and the environment.
The objective of safety systems is to reduce the risk for humans and machines that is posed by
a use case to an acceptable level. The 󹪝rst step is, therefore, to identify the risk of a use case. In
order to make a reliable assessment regarding the application, each individual function of a
machine or plant must be analyzed for potential hazards.
You can 󹪝nd further information on the Siemens Safety Integrated (http://www.siemens.com/
safety) Internet page.
3.7.3 Basic terminology
3.7.3.1 Redundancy/single-channel and two-channel
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 con󹪝guration reduces the probability of a function failing due to a single defective
component. This requirement is essential for achieving SILCL 3 as per EN 62061, SIL 3 as per
IEC 61508 and PL e/Cat. 4 as per EN ISO 13849-1 (also necessary for SILCL 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 con󹪝guration, the subsystems for detecting and reacting must also be
implemented with two-channel redundancy.
Note
All safety devices that comply with SILCL 3 as per EN 62061, SIL 3 as per IEC 61508 and PL e/Cat. 4
as per EN ISO 13849-1 are redundantly con󹪝gured with regard to the internal logic and also with
regard to the output circuits.
Overview
3.7 Safety systems - General information
SIRIUS 3RK3 Modular Safety System
Equipment Manual, 07/2020, NEB926253002000/RS-AC/006 51