Glossary · PLC and control programming
IEC 61131-3
Also known as: IEC 61131 Part 3, EN 61131-3
German: IEC 61131-3
IEC 61131-3 is the international standard that defines the programming languages, data types, program organization units and software model for programmable logic controllers, including ladder diagram, function block diagram, structured text and sequential function chart.
- PLC programming
- Standards
In one sentence
IEC 61131-3 is the international standard for PLC programming languages, data types, program units and the PLC software model.
Example
A machine builder writes its specification so that all control software follows IEC 61131-3, with structured text for calculations and SFC for sequences.
How it applies
- Engineering: IEC 61131-3 gives PLC programming a common vocabulary: configurations, resources, tasks, programs, function blocks, functions, elementary and derived data types, and the languages LD, FBD, ST and SFC (the 2013 edition marked IL as deprecated). It also introduced object-oriented features such as methods, interfaces and inheritance.
- Portability: Vendors implement the standard to different degrees and add extensions. Code written to IEC 61131-3 is easier to port, but rarely portable without changes. PLCopen works on harmonization, and PLCopen XML provides an exchange format.
- Safety: IEC 61131-3 is a programming standard, not a safety standard. Safety-related software follows IEC 61508, IEC 61511, IEC 62061 or ISO 13849-1, usually with a restricted language subset.
- Documentation: Use the standard's terms (task, program, function block, data type) in software documentation and glossaries. Readers across vendors then understand them the same way.
IEC 61131-3 vs. IEC 61499
IEC 61131-3 describes cyclically executed programs on a controller. IEC 61499 describes event-driven function block applications distributed across several devices. They can coexist, and IEC 61499 reuses IEC 61131-3 data types and ST for algorithms.