IEC 61131-3 represents the first real attempt to standardize programming languages in industrial automation. The legislation is the result of hard work carried out by seven international companies that have brought over ten years of experience in the industrial automation sector. The standard has a worldwide diffusion and is independent of the systems manufacturers. Manufacturers such as Siemens (STEP7), Schneider, Omron, ABB, Festo, etc. have conformed to this standard.
The IEC 61131-3 is the third part of the IEC 61131 standard, which consists of:
- Part 1 - General overview
- Part 2 - Hardware Requirements
- Part 3 - Programming languages
- Part 4 - User guidelines
- Part 5 - Communication
- Part 6 - Security
- Part 7 - Fuzzy logic
- Part 8 - Application guidelines
Programming languages
Five programming languages are defined in the standard. This means that its syntax and semantics have been defined, making it impossible to use dialects. Once learned, a variety of systems can be used based on this standard. The languages consist of two text versions and three graphic versions, please refer to the note "Definitions on IEC61131-3 standards”Edited by Cesare Fantuzzi and Marcello Bonfè.
Textual
- The Instruction List (IL) is its European correspondent. As a textual language, remember assembler.
- Structured Text (ST) is a very powerful high-level language that originates in Ada, Pascal and "C". It contains all the fundamental elements of a modern programming language, including selective instructions (IF-THEN-ELSE and CASE OF) and iterative loops (FOR, WHILE and REPEAT). These elements can also be nested. An excellent use of structured text is to create complex function blocks which can themselves be used within all other languages.
Graphs
- The Contact Diagram (LD) originates in the USA, it is based on the graphical presentation of a relay circuit.
- The Function Block Diagram (FBD) is very popular in the process industry. It expresses the behavior of functions, function blocks, and programs as a group of interconnected graphic blocks, such as in electronic circuit diagrams. Consider a system from the point of view of the flow of signals acting between processing elements.
- The Sequential Functional Diagram (SFC) is based on the Grafcet which in turn inherits the main characteristics from the mathematical model of the Petri Net. The SFC is also useful as a modeling and analysis tool for the sequential evolution of an automation system as it allows the machine cycle to be decomposed into a series of sequential control actions.
Which language to choose
All five languages are managed by a common suite that allows the entire project to be divided into different programs written in the 5 different languages. The programming language to choose depends on several factors including:
- the basic knowledge of the programmer
- the type of problem to be solved
- the level of description of the problem
- the structure of the control system
- the interface with other people / other departments
Why program in IEC61131-3
There are countless advantages to using the IEC61131-3 standard including:
- Easy migration to and from different hardware platforms of different manufacturers (Siemens, Omron, Schneider etc.),
- Protection of the investment both at the training level and at the application level,
- Compliance with the requirements of the EN60204 machine directive,
- Reusability of the developed application.