What is the difference between SIL and PL?
SIL (Safety Integrity Level) focuses on the probability of failure, whilst PL (Performance Level) assesses the reliability of the entire safety system.
Are you working on machine safety and are you unsure which standard you need? We explain it clearly below.
SIL and PL are both standards for machine safety.
The main difference is:
SIL is primarily used within IEC 61508 and IEC 62061.
PL is derived from the EN ISO 13849 standard.
In many applications, they are comparable, but the calculation and approach differ.
SIL is a measure of how reliable a safety function is, based on the probability of its failure.
There are four levels:
SIL is determined based on:
SIL is widely used in the process industry and in complex installations.
PL indicates how well a safety system performs in the field of mechanical engineering.
There are five levels:
PL is determined by:
PL is the most widely used standard in mechanical engineering.
Although SIL and PL come from different standards, they have the same purpose:
making machines and installations demonstrably safe.
| SIL | PL |
|---|---|
| IEC 61508 / IEC 62061 | EN ISO 13849 |
| Based on probability of failure | Based on system performance |
| SIL 1 – SIL 4 | PL a – PL e |
| Widely used in the process industry | Standard in mechanical engineering |
In many applications, SIL and PL are comparable, if calculated and applied correctly.
Choose SIL when:
Choose PL when:
In many projects, the standard determines which method you use.
Safety sensors and encoders play a crucial role in achieving SIL and PL levels.
At Procim, we can assist with:
Always tailored to your machine and risk level.
SIL and PL both describe the safety level of a safety function.
SIL focuses primarily on the probability of failure,while PL looks at the total system structure,including component reliability and diagnostics.
Within mechanical engineering, PL (EN ISO 13849-1) is usually applied.
SIL (IEC 62061) is more commonly used for more complex or process-oriented installations. The choice depends on the standard applicable to your machine.
Yes. Many safety sensors and encoders are certified for both SIL and PL, making them widely applicable in safety functions.
Not necessarily. The security level must match the risk..
Too high a level can be unnecessarily complex and costly, while too low a level offers insufficient security.
Yes. Procim will consider your application and advise you on suitable sensors, encoders and safety solutions that meet the required SIL or PL classification.
The standard does not prescribe a specific level, but does require a risk analysis,The result determines which SIL or PL level is required to comply with the machinery guidelines.
Yes, there are guidelines for comparing SIL and PL, but this must be done carefully.
No, the appropriate level depends on the risk assessment.
That depends on the application and the industry.
We’ll help you choose the right safety solution for your application.