IEC 61131-3

Introduction to IEC 61131-3 Standard

IEC 61131-3 is an international standard for programmable logic controllers (PLCs). Don't worry if you're not familiar with PLCs yet. They're essentially specialized computers used to control industrial processes, like assembly lines or robotic devices.

What is IEC 61131-3?

IEC 61131-3 is the third part of the IEC 61131 family. It defines the basic software architecture and programming languages of PLCs. Before this standard, every PLC manufacturer had their own unique programming languages and conventions. This made it difficult for engineers to work with different PLCs. IEC 61131-3 was created to standardize PLC programming, making it easier for engineers to learn and use these systems.

Programming Languages

IEC 61131-3 defines five programming languages:

  1. Ladder Diagram (LD): This is a graphical language that represents circuits in a form of a diagram.

  2. Structured Text (ST): This is a high-level language similar to Pascal or C.

  3. Instruction List (IL): This is a low-level language similar to assembly language.

  4. Function Block Diagram (FBD): This is a graphical language that allows you to build complex procedures by connecting function blocks.

  5. Sequential Function Chart (SFC): This is a graphical language used for sequential and parallel process control tasks.

Each of these languages has its own strengths and weaknesses, and the best one to use depends on the specific task at hand.

Why is IEC 61131-3 Important?

IEC 61131-3 is important because it provides a standardized way to program PLCs. This means that if you learn to program in these languages, you'll be able to work with PLCs from many different manufacturers. It also makes it easier to share code between different PLCs, and to move code from one PLC to another. Not every PLC supports all five languages, but most support at least two or three of them. This means that you can use the same code on different PLCs, even if they don't support the same languages. Some PLCs are not fully complient with the standard, but they still support most of the features.


IEC 61131-3 is a key standard in the world of industrial automation. By standardizing the programming languages and software architecture of PLCs, it makes it easier for engineers to learn, use, and share PLC programming. If you start your journey into the world of PLCs, understanding IEC 61131-3 will be a valuable asset.

We are diligently working to ensure that our PLC Simulator Online (opens in a new tab) is fully compliant with the IEC 61131-3 standard, striving to provide a high-quality, industry-standard tool for our users.

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