engineering

IEC 61131

IEC 61131 is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand IEC 61131 rather than just read about it. In short: IEC 61131 is an IEC standard for programmable controllers. It was first published in 1993; the current (4th) edition dates from 2025.

Key takeaways

IEC 61131 belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect IEC 61131 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of IEC 61131 from memory before moving on to harder problems.

Reference excerpt

IEC 61131 is an IEC standard for programmable controllers. It was first published in 1993; the current (4th) edition dates from 2025. It was known as IEC 1131 before the change in numbering system by IEC. The parts of the IEC 61131 standard are prepared and maintained by working group 7, programmable control systems, of subcommittee SC 65B of Technical Committee TC65 of the IEC.

Sections of IEC 61131 Standard IEC 61131 is divided into several parts:

Part 1: General information. It is the introductory chapter; it contains definitions of terms that are used in the subsequent parts of the standard and outlines the main functional properties and characteristics of PLCs. Part 2: Equipment requirements and tests - establishes the requirements and associated tests for programmable controllers and their peripherals. This standard prescribes: the normal service conditions and requirements (for example, requirements related with climatic conditions, transport and storage, electrical service, etc.); functional requirements (power supply & memory, digital and analog I/Os); functional type tests and verification (requirements and tests on environmental, vibration, drop, free fall, I/O, power ports, etc.) and electromagnetic compatibility (EMC) requirements and tests that programmable controllers must implement. This standard can serve as a basis in the evaluation of safety programmable controllers to IEC 61508. Part 3: Programming languages Part 4: User guidelines Part 5: Communications Part 6: Functional safety Part 7: Fuzzy control programming Part 8: Guidelines for the application and implementation of programming languages Part 9: Single-drop digital communication interface for small sensors and actuators (SDCI, marketed as IO-Link) Part 10: PLC open XML exchange format for the export and import of IEC 61131-3 projects

Related standards IEC 61499 Function Block PLCopen has developed several standards and working groups.

TC1 - Standards TC2 - Functions TC3 - Certification TC4 - Communications TC5 - Safe Software TC6 - XML Motion Control Library Presentation on IEC 61131-3

References

Sources R.W. Lewis, Modelling control systems using IEC 61499 R.W. Lewis, Programming industrial control systems using IEC 1131-3 K.H. John & M. Tiegelkamp, IEC 61131-3: Programming Industrial Automation Systems

External links "IEC 61131" at International Electrotechnical Commission PLCopen.org - International Not-For-Profit organization that supports and extends the IEC 61131 programming standard. http://www.PLCopen.org PLCopen North America http://www.PLCopen-NA.org Part of PLCopen XML Standard Documentation

Worked examples

Example 1 — a first encounter with IEC 61131

Start with the simplest possible case. Write down what IEC 61131 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to IEC 61131 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about IEC 61131 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of IEC 61131

In research: IEC 61131 appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses IEC 61131 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: IEC 61131 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electronic engineering, IEC 61131, IEC standards, so understanding it makes those chapters shorter.
In everyday life: Look for IEC 61131 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study IEC 61131 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what IEC 61131 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain IEC 61131 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IEC 61131 in simple terms?

IEC 61131 is an IEC standard for programmable controllers. It was first published in 1993; the current (4th) edition dates from 2025.

Why does IEC 61131 matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study IEC 61131?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on IEC 61131.