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What is IEC61131-3? What is PLCopen?

What is IEC61131-3?

IEC 61131-3 standard is the only global standard for industrial control programming. It harmonizes the way people design and operate industrial controls by standardizing the programming interface. A standard programming interface allows people with different backgrounds and skills to create different elements of a program during different stages of the software lifecycle: specification, design, implementation, testing, installation and maintenance. Yet all pieces adhere to a common structure and work together.

The standard includes the definition of the Sequential Function Chart (SFC) language, used to structure the internal organization of a program, and four inter-operable programming languages: Instruction List (IL), Ladder Diagram (LD), Function Block Diagram (FBD) and Structured Text (ST). Via decomposition into logical elements, modularization and modern software techniques, each program is structured, increasing its re-usability, reducing errors and increasing programming and user efficiency.

IEC 61131-3 is section 3 of the IEC61131 standard. It specifies the syntax and semantics of a unified suite of programming languages for programmable controllers(PCs) and programmable logic controllers (PLCs).  This suite consists of two textual languages, Instruction List (IL) and Structured Text (ST), and two graphical languages, Ladder Diagram (LD) and Function Block Diagram (FBD).

An additional set of graphical and equivalent textual elements named Sequential Function Chart (SFC) is defined for structuring the internal organization of programmable controller programs and function blocks. Also, configuration elements are defined which support the installation of programmable controller programs into programmable controller systems.

In addition, features are defined which facilitate communication among programmable logic controllers and other components of automated systems.

Other parts of IEC61131 exist which detail definitions (1), equipment requirements & tests (2),  user guidelines (4), messaging services (5), functional safety (6), fuzzy logic (7), guidelines for programming (8).

Further details available on IEC's website:


What is PLCopen?

Software plays an ever-increasing role in industrial automation. With this, the associated software costs increase, even to the point that it becomes the highest part of the total system. And not all costs are directly visible: the required maintenance over the life cycle, adding new functionalities, coping with new governmental rules.

To control these costs, one needs higher efficiency during the application development, while increasing the software quality.

PLCopen, as an organization active in Industrial Control, is creating a higher efficiency in your application software development and lowering your life-cycle costs. As such it is based on standard available tools to which extensions are and will be defined. With results like Motion Control Library, Safety, XML specification, Reusability Level and Conformity Level, PLCopen made solid contributions to the community, extending the hardware independence from the software code, as well as reusability of the code and coupling to external software tools.

PLCopen is a vendor- and product-independent worldwide association. Its mission is to be the leading association resolving topics related to control programming to support the use of international standards in this field. For this PLCopen has several technical and promotional committees with participants from numerous large industrial manufactures of PCs and PLCs.

PLCopen was founded in 1992 and has headquarters in The Netherlands with supporting offices in the USA, Japan, and China.

Further details available on PLCopen's website: