Anyone working on machine safety quickly runs into two acronyms that seem to measure the same thing but come from different standards: SIL (Safety Integrity Level, IEC 61508 / IEC 62061) and PLe (Performance Level, EN ISO 13849-1). Understanding the difference avoids design mistakes, especially when one component is certified under one standard and the rest of the circuit was validated under the other.
Two standards, two approaches
EN ISO 13849-1 was written for machinery safety and uses the Performance Level (from PLa to PLe), a rating that combines component reliability (MTTFd), circuit structure (category) and diagnostic coverage (DC). It’s the most common approach for relatively simple safety circuits: barriers, interlocked guards, emergency stops.
IEC 62061 (the machinery-sector version of IEC 61508) uses SIL (from SIL1 to SIL3) and is built for more complex safety architectures, typically based on safety PLCs and safety fieldbus networks.
When to use which
In practice, many designers use EN ISO 13849-1 for most machine applications, and switch to IEC 62061 when the safety architecture is distributed across a fieldbus (e.g. TwinSAFE, PROFIsafe) with multiple interconnected safety stations.
The point not to overlook
SIL and PLe are not an automatic conversion table: a SIL2-rated component doesn’t mechanically equal a PLd. The standards provide indicative correspondence tables (e.g. IEC 62061 Annex A), but the calculation must always be redone on the actual circuit architecture, not just on the single component.
If you’re evaluating a compliance upgrade on an existing plant or designing a new safety circuit, the correct starting point is always risk assessment per EN ISO 12100: that’s where the required performance level comes from, not from the datasheet of the component you’d like to use.