Choosing an Automation Platform: Compliance with IEC 61131

IEC 61131 was published in 1993 after over 10 years of development by IEC (the International Electrotechnical Commission). The 10-part standard is an attempt to standardize programmable controllers.

Each of the 10 parts addresses a different part of the programmable controller. Parts are identified by the number following the standard, such as “IEC 61131-1.”

Here are all 10 parts of the standard:

  • Part 1: General Information;
  • Part 2: Equipment requirements and tests;
  • 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 (SDCI);
  • Part 10 (Under development): XML exchange formats for programs according to IEC 61131-3.

Standards are platform independent, which means that ideally, automation systems following the standard can be ported from one platform to another. However, this is not always the case in practice because each automation vendor has special functions and tools that apply only to their hardware. At a basic level, though, a code base developed in one platform will work on another platform as long as both conform to this standard.

Key Programming Parts of the Standard

Two of the most commonly known parts of this standard are part 3 and part 9. Part 3 deals with programming languages and part 9 is known as Single-drop Digital Communication Interface, SDCI, or more commonly “IO-Link.”

Part 3 defines modern PLC programming languages: Structured Text (ST), Instruction List (IL), Ladder Diagram (LD), Function Block Diagram (FBD), and Sequential Function Charts (SFC).

This part of standard details the elementary data types and the way that user data types are defined. Compliance with this standard means that data types are consistent across platforms. It means that an integer on platform A is the same size as an Integer on platform B.

It also describes the types and scope of variables in a PLC (Global, Local, I/O, External, and Temporary) and it defines the program configuration details, like Tasks and Programs. It also defines Program Organization Units (POU). These include Functions and Function Blocks. In the Rockwell world, these are called Add-on Instructions (AOIs), while most other platforms call them Functions or Function Blocks (not to be confused with Function Block Diagram programming language).

Part 8 of the standard is a technical report on how to put all the parts from Part 3 together. This part is a software development guide using the standards from Part 3

Part 10 of the standard is still under development, but it describes an XML schema for exchanging programs according to Part 3, which would enable you to take your program from one platform to another without a problem.

Whatever automation platform you choose, it is important that it meets IEC 61131. Nearly all modern platforms conform to this standard in some way. Using a system integrator company that knows this standard means that you will not be limited to any specific industrial automation platform and opens the possibilities of options.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our industrial automation services, or selecting a platform that follows the IEC standard contact Terry DuMoulin.

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