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Should I Use ISO 13849-1 or IEC 62061
ISO 13849-1 and IEC 62061 are two widely used standards for designing a machine's safety circuit. Both start at the risk assessment, set the level each safety function must reach (probability of failure), and end with validating the safety function. The main difference, however, is how they rate a safety function. ISO 13849-1 uses five Performance Levels, PL a to PL e, while IEC 62061 is the machinery standard within the IEC 61508 framework and uses Safety Integrity Levels, SIL 1 to SIL 3. Both ratings are based on the average frequency of a dangerous failure per hour (PFH) and can therefore be directly related to one another.
PL | PFHd | SIL |
|---|---|---|
a | 10⁻⁵ to < 10⁻⁴ | N/A |
b | 3×10⁻⁶ to < 10⁻⁵ | SIL 1 |
c | 10⁻⁶ to < 3×10⁻⁶ | SIL 1 |
d | 10⁻⁷ to < 10⁻⁶ | SIL 2 |
e | 10⁻⁸ to < 10⁻⁷ | SIL 3 |
Subsystems designed to either standard can be combined into one safety function, as allowed in ISO 13849-1. For example, a custom logic board's PFH can be determined using IEC 62061, but then combined into a broader safety function calculation using SISTEMA (ISO 13849-1).
ISO 13849-1 applies to any technology, including electrical, hydraulic, pneumatic and mechanical systems, and its designated architectures (Categories B, 1, 2, 3 and 4) simplify the calculation. IEC 62061 was originally limited to electrical and electronic systems and its way of building safety functions from subsystems is more flexible for complex designs.
In practice, ISO 13849-1 is used far more often due to its simplicity and ease-of-use due to the free software, SISTEMA.
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