Glossary · Functional safety
Performance Level (PL)
Also known as: PL
German: Performance Level (PL)
In functional safety of machinery, a Performance Level (PL) is a discrete level used in ISO 13849-1 to specify the ability of safety-related parts of control systems to perform a safety function under foreseeable conditions. There are five levels, PL a to PL e, with PL e the highest.
- Functional safety
- Verification
In one sentence
The Performance Level (PL a to e) expresses how reliably safety-related control parts perform a safety function under ISO 13849-1.
Example
The safety function “stop the robot when the light curtain is interrupted” is designed and verified to PL d, which meets the PLr d determined in the risk assessment of the robot cell.
How it applies
- Functional safety: The achieved PL is determined from the Category, MTTFd, diagnostic coverage, measures against common-cause failure and, for software, systematic measures. Each PL corresponds to a range of average probability of dangerous failure per hour.
- Verification: The achieved PL must be equal to or higher than the required Performance Level of the same safety function. Tools such as SISTEMA support the calculation, but the input data remain the designer's responsibility.
- Technical documentation: Name the achieved PL per safety function, not per machine. "The machine is PL d" is an imprecise statement that users and auditors may misread.
- Evidence: The PL claim needs the calculation, component data, fault analysis and validation per ISO 13849-2 behind it.
Performance Level vs. SIL
PL comes from ISO 13849-1 and SIL from IEC 62061 and IEC 61508. Both express the reliability of safety functions and can be mapped approximately via their probability ranges, but they are determined with different methods. Do not convert one into the other without stating the basis.