Glossary · Functional safety
Safety PLC
Also known as: safety programmable logic controller, safety controller
German: Sicherheits-SPS
In functional safety, a safety PLC is a programmable logic controller designed and certified for safety-related control functions. Its internal redundancy, self-tests and certified firmware support safety functions up to the level stated in its certificate, under the conditions of its safety manual.
- Functional safety
- Integrated systems
In one sentence
A safety PLC is a programmable controller designed and certified for safety functions, used within the limits of its certificate and safety manual.
Example
An AGV charging area uses a safety PLC to evaluate laser scanners, door switches and emergency stops, and to command Safe Torque Off on the conveyor drives.
Explained in context
Context cards connect this term with others to answer one question. Also in British English and German.
How it applies
- Functional safety: The certificate covers the controller, not the application. The safety program, wiring, sensors and actuators still need their own design, verification and validation.
- Evidence: Keep the safety program version, its checksum or signature, and the validation report together. The checksum is a practical way to show that the validated program is the one running.
- Change control: Any change to the safety program is a change to safety functions. It needs impact analysis, re-verification and a controlled release through change control.
- Technical documentation: The safety manual of the controller sets conditions such as response times, proof test intervals and permitted configurations. Carry the relevant conditions into the machine's own documentation.
Safety PLC vs. safety relay
A safety relay performs one or a few fixed functions with limited configuration. A safety PLC is programmable, handles many functions and signals, and therefore needs software verification and stricter version control.