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IEC 61131-3: Programmable Controllers - Part 3: Programming Languages

Title: A Comprehensive Guide to IEC 61131-3: Programmable Controllers Programming Languages




IEC 61131-3 is an international standard for programmable logic controller (PLC) programming, established by the International Electrotechnical Commission (IEC). This standard defines a set of programming languages that can be used to develop PLC applications. In this article, we will explore the different programming languages specified in IEC 61131-3 and discuss their features, capabilities, and applications.


Overview of IEC 61131-3


IEC 61131-3 is divided into several parts, with Part 3 focusing on programming languages for programmable controllers. The standard specifies five programming languages that can be used to develop PLC applications:


1. Structured Text (ST): ST is a high-level programming language that resembles Pascal or C. It allows developers to write complex algorithms in a clear and structured manner. ST is suitable for developing mathematical calculations, data processing, and complex control algorithms.


2. Function Block Diagram (FBD): FBD is a graphical programming language that uses interconnected blocks to represent logic functions. It is easy to understand and is commonly used for developing control algorithms and sequences.


3. Ladder Diagram (LD): LD is a graphical programming language that mimics the traditional relay ladder logic used in industrial automation. It is intuitive and easy to visualize, making it suitable for developing simple control logic.


4. Instruction List (IL): IL is a low-level programming language that represents PLC instructions in a textual format. It is similar to assembly language and is used for writing direct control sequences.


5. Sequential Function Chart (SFC): SFC is a graphical programming language that divides the control logic into steps or stages. It is suitable for developing complex control sequences and state-based logic.


Each programming language in IEC 61131-3 has its strengths and weaknesses, and the choice of language depends on the requirements of the application and the preferences of the developer.


Features and Benefits of IEC 61131-3 Programming Languages


One of the key benefits of using IEC 61131-3 programming languages is the standardization they provide. By adhering to the defined syntax and semantics of the languages, developers can create consistent and reliable PLC applications that are easier to maintain and troubleshoot.


Another benefit of IEC 61131-3 programming languages is their flexibility. Developers can choose the most suitable language for each part of the application, depending on the complexity and requirements of the logic. This allows for better optimization and efficiency in PLC programming.


IEC 61131-3 programming languages also promote modularity and reusability. With the use of function blocks and reusable code segments, developers can create modular and scalable PLC programs that can be easily adapted and extended for different applications.


Applications of IEC 61131-3 Programming Languages


IEC 61131-3 programming languages are widely used in various industries, including manufacturing, energy, transportation, and building automation. Some common applications of these languages include:


- Control of manufacturing processes, such as assembly lines, packaging machines, and CNC machines

- Monitoring and control of power distribution systems, including transformers, switchgear, and substations

- Automation of transportation systems, such as railway signaling, traffic lights, and toll collection

- Building automation systems, including HVAC control, lighting control, and security systems


By utilizing IEC 61131-3 programming languages, developers can create robust and reliable PLC applications that meet the stringent requirements of industrial automation.




IEC 61131-3 programming languages provide a standardized and flexible approach to developing PLC applications. By understanding the features and benefits of the different languages specified in the standard, developers can create efficient and reliable control logic for a wide range of industrial automation applications.


Whether using Structured Text, Function Block Diagram, Ladder Diagram, Instruction List, or Sequential Function Chart, it is important to choose the most suitable language for each part of the application to ensure optimal performance and maintainability.


By mastering IEC 61131-3 programming languages, developers can enhance their skills and expertise in industrial automation, paving the way for a successful career in the field of programmable controllers.



Contact: Eason Wang

Phone: +86-13751010017


Add: 1F Junfeng Building, Gongle, Xixiang, Baoan District, Shenzhen, Guangdong, China

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