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Introduction to Functional Safety of Control Systems
IEC/EN 62061 describes both the amount of risk to be reduced and the ability of a control system to reduce that risk in terms of SIL (Safety Integrity Level). There are three SILs used in the machinery sector, SIL 1 is the lowest and SIL 3 is the highest.
Because the term SIL is applied in the same manner in other industrial sectors such as petro-chemicals, power generation and railways, IEC/EN 62061 is very useful when machinery is used within those sectors.
Risks of greater magnitude can occur in other sectors such as the process industry and for that reason IEC 61508 and the process sector specific standard IEC 61511 include SIL 4.
A SIL applies to a safety function. The subsystems that make up the system that implements the safety function must have an appropriate SIL capability. This is sometimes referred to as the SIL Claim Limit (SIL CL).
A full and detailed study of IEC/EN 62061 is required before it can be correctly applied. Some of the most commonly applicable requirements of the standard are summarized later in this text.