Glossary · Functional safety
Safety function
German: Sicherheitsfunktion
In functional safety, a safety function is a function whose failure can increase risk and that is implemented to achieve or maintain a safe state. Each safety function is specified with its trigger, reaction, required level (PLr or SIL) and response time.
- Functional safety
- Systems engineering
In one sentence
A safety function is a control function whose failure raises risk; each one is specified, rated and verified separately.
Example
“When the guard door of the robot cell opens, the robot drives are brought to a stop and Safe Torque Off is maintained until the door is closed and reset” is one safety function.
How it applies
- Functional safety: The safety function, not the component, is the unit of design and verification. It runs from the sensor through the logic to the actuator and has its own PL or SIL.
- Risk reduction: Each safety function should trace to a hazard and to the risk reduction it is credited with in the risk assessment.
- Technical documentation: Maintain a safety function list with a unique ID, description, trigger, reaction, defined safe state, required and achieved level, and response time. The operating manual should describe the functions users interact with, such as reset and muting.
- Evidence: Validation tests are organized per safety function, which makes the list a natural backbone for traceability.
Safety function vs. protective device
A light curtain is a protective device. The safety function is the whole behavior: detection, evaluation, stopping the hazardous movement and preventing restart.