Glossary · Functional safety
Programmable logic controller (PLC)
Also known as: PLC, standard PLC
German: Speicherprogrammierbare Steuerung (SPS)
In industrial automation, a programmable logic controller (PLC) is an industrial controller used to automate machine and process functions. A standard PLC is not automatically safety-rated and cannot be assumed to perform safety functions.
- Functional safety
- Integrated systems
In one sentence
A programmable logic controller (PLC) automates machine and process functions, but a standard PLC is not safety-rated by default.
Example
On a bottling line, a standard PLC sequences the filler, capper and labeler, while the guard doors and emergency stops are handled by a separate safety PLC.
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: Using a standard PLC for a safety function requires the full evidence of ISO 13849-1 or IEC 62061, which is rarely practical. Safety functions usually go to a safety PLC or safety relay.
- Integrated systems: The standard PLC often coordinates several machines and exchanges data with MES and cloud systems. Its signals to the safety system must be defined so that it cannot override a safety function.
- Cybersecurity: Networked PLCs are attack targets. IEC 62443 addresses zones, conduits and access control.
- Technical documentation: Document program versions and the parameters that affect machine behavior, so that changes can be traced.
Standard PLC vs. safety PLC
A standard PLC is built for availability and flexibility. A safety PLC is designed and certified for safety functions, with internal redundancy, self-tests and a safety manual that sets conditions of use.