SIL & Performance Level — functional safety for machinery.

Safety functions need a demonstrable measure. In mechanical engineering there are two worlds for this — SIL and Performance Level — that translate directly into each other.

Discuss control & safety

IEC 61508 — the parent standard

IEC 61508 is the overarching standard for functional safety of electrical/electronic/programmable systems. It defines Safety Integrity Level (SIL) 1 to 4 — the higher the level, the stricter the requirements.

IEC 62061 — SIL for machinery

IEC 62061 transfers the SIL concept to machine controls and uses SIL 1 to 3 (SIL 4 is excluded for machinery). It covers electrical, electronic and programmable controls.

ISO 13849 — Performance Level (PL)

ISO 13849 uses the Performance Level PL a to e (a = lowest, e = highest safety) and covers a broader range of technologies — including pneumatics and hydraulics. The PL is defined via the average probability of a dangerous failure per hour.

The translation

Both standards are harmonized under the machinery legislation and are considered equivalent. The levels map directly: PL e ≙ SIL 3, PL d ≙ SIL 2, PL c ≙ SIL 1. We implement safety functions in the control system and PLC accordingly — we clarify the exact framework on a project-specific basis.

Frequently asked questions

SIL or PL — which should I use?

Both are recognized under the machinery legislation and are equivalent. ISO 13849 (PL) also covers non-electrical technologies; IEC 62061 (SIL) focuses on electrical/programmable controls. The choice depends on the technology and the project context.

Is this related to ISO 26262?

Conceptually yes — they all come from the world of functional safety (with IEC 61508 as the root). ISO 26262 is the automotive variant; for machinery, IEC 62061 / ISO 13849 apply. See also our article on functional safety in automotive.

Sources: Automation World — PL & SIL, SIL vs. PL (IEC 62061 vs. ISO 13849). The valid version of the standard is authoritative.