Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Safety standards

IEC 61131

German: IEC 61131

IEC 61131 is the international standard series for programmable controllers (PLCs), covering general information, equipment requirements and tests, programming languages (Part 3), user guidelines, communications and functional safety for PLCs (Part 6), among other parts.

  • Standards

In one sentence

IEC 61131 is the standard series for programmable controllers (PLCs), including equipment requirements and the programming languages in Part 3.

Example

A machine builder specifies that all PLC code must be written in IEC 61131-3 Structured Text and function block diagram to ease maintenance by the customer.

How it applies

  • Engineering: IEC 61131-3 defines the programming languages (Structured text (ST), ladder diagram, function block diagram, sequential function chart; instruction list is deprecated in the current edition) and the program organization units.
  • Hardware: IEC 61131-2 defines requirements and tests for PLC equipment (environment, I/O characteristics).
  • Safety: IEC 61131-6 addresses functional safety of PLCs; safety PLCs are also assessed against IEC 61508.
  • Documentation: Programming manuals and code documentation should use IEC 61131-3 terms (POU, function block, task); the documentation team should note where a vendor's implementation deviates.

Customers often require IEC 61131-3 compliant programming; check which languages and features a controller actually supports.

IEC 61131 vs. IEC 61499

IEC 61131-3 targets cyclic programming of individual controllers. IEC 61499 defines an event-driven function block model for distributed control applications.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: IEC 61131 series, Programmable controllers

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Blog and are not part of any standard.

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