What is Performance Level (PL)?
Performance Level (PL) is a measure of the reliability and effectiveness of safety functions in machines. It is used in the NEN-EN-ISO 13849 standard to indicate how well a system can prevent the risk of injury or damage.
PL is essential for designing and assessing emergency stop circuits, light curtains, door interlocks and other machine safeguards within the scope of the Machinery Directive.
🧠 How does Performance Level work?
- Carry out a risk assessment
- Determine the required Performance Level (PLr) using the risk graph
- Based on:
- Severity of injury (S)
- Frequency/exposure (F)
- Possibility of avoiding the hazard (P)
- Design the safety function
- Selection of suitable components: safety relays, Safety PLC, sensors
- Assessment of:
- MTTFd (Mean Time To Dangerous Failure)
- DC (Diagnostic Coverage)
- Category (system architecture)
- Calculating the achieved PL (a to e)
- Use of software such as SISTEMA or manual calculation
- Validation and documentation are mandatory
🏭 Use in industrial automation
- Safe switching of motors, Drives and Soft Starters
- Use in control cabinets, robot cells and packaging lines
- Emergency stop, light curtain, door interlock, two-handed operation
- Compatible with Lock-out Tag-out and work-permit procedures
PL is particularly suited to electrical, electronic and mechanically based systems, and does not require programmable logic as SIL does.
🔍 PL levels explained
| PL | Meaning | Use |
|---|---|---|
| a | Low – little reliability required | Minor risks, limited exposure |
| b | Basic safety | Simple applications without serious consequences |
| c | Medium | Most common in standard machines |
| d | High | Robots, presses, moving parts with risk |
| e | Very high – life-threatening | Heavy machinery with high risk of severe injury |
PLr = the required level, PL = the level achieved. They must at least be equal.
🔐 Compliance and design considerations
- Selection of certified components (CE, TÜV, SIL/PL-rated)
- Detection of faults (short circuits, broken wires) is mandatory from PL c onwards
- Diagnostics and redundancy are important at PL d and e
- Periodic reassessment as part of the risk assessment or Audit
- Integrate with PPE, Lock-out Tag-out and training
Take note: choosing the wrong PL = insufficient protection and non-compliance with the Machinery Directive.
📌 In summary
PL is a standardised way of measuring how reliable a safety function in a machine is. It helps reduce risk and meets the requirements of the Machinery Directive and ISO 13849.