- By Bill Lydon
- February 28, 2022
A brief overview of PLCopen and the IEC 61131-3 industrial control software standard.
Industrial automation and control has been ahead of the latest computer industry buzz about no-code development platforms (NCDPs) since 1969 with visual ladder logic programming and evolving into the IEC 61131-3 International Electrotechnical Commission (IEC) standard, first published in 1993. The standard continues to be enhanced and extended in IEC committees and by the not-for-profit PLCopen trade organization, which is comprised of a broad range of volunteer industry experts continually defining and adding new functions to meet new industry needs. Noteworthy enhancements include industrial safety, motion control, robotics, OPC UA, and other functions described on the PLCopen website.
The goal continues to be empowering industrial and process engineers to create applications without being computer programmers.
International Electrotechnical Commission
Founded in 1906, the International Electrotechnical Commission (IEC) is a worldwide organization that publishes standards covering a vast range of technologies including industrial automation and controls, power generation, transmission and distribution, semiconductors, fiber optics, batteries, solar energy, nanotechnology, and marine energy as well as many others.
First no-code industrial programming—1969
Dick Morley is considered the father of the programmable logic controller (PLC), a computer with industrial inputs and outputs conceived by his team at Bedford Associates. The ladder logic control language used electrical relay symbols for users to visually program control and automation the same way they designed physical relay panels (Figure 1). The advantage was the language could be understood by any working electrician in the world.
The first no-code industrial control programming was ladder logic used to program the Modicon 084 PLC deployed at General Motors to control metal cutting, hole drilling, material handling, assembly, and testing for the Hydramatic Model 400 automatic transmission. The new system replaced the large electromagnetic relay panels using a fraction of the space, consuming less energy, and increasing reliability. Labor and downtime for model changeovers was drastically reduced by programming rather than rewiring hundreds of relays.
The PLC enabled significant industrial control and automation applications to be done, dramatically advancing manufacturing productivity, quality and profits.
Birth of IEC 61131-3
The IEC 61131-3 industrial control software standard started with ladder logic (LL) and enhanced the language capabilities and ease of use with function block (FB) and sequential function chart (SFC) programming. Further enhancements have been defined and standardized by PLCopen.
The IEC 61131-3 industrial control software standard is widely used. It enables manufacturing and process engineers to create applications without writing any code. Plant and process people create application programs visually in IEC 61131-3 graphical integrated design environments (IDE) to build, simulate, debug, and download code to PLCs, distributed control systems (DCS), and a wide range of other real-time controllers.
IEC 61131-3 defines strong data typing that includes Boolean, integer, real, string, time, vendor defined, user defined, and physical input/output (I/O).
In addition to ladder logic, the standard supports other programming methods that are compatible with each other. They include function block diagram; structured text; sequential function chart; and user-defined functions created using ladder logic, function block, and structured text.
Function blocks. The function block diagram (FBD) is a graphical language that describes the function between input variables and output variables. Inputs and outputs of the blocks are wired together with connection lines or links (Figure 2).
There are a wide range of function blocks. For example:
- Mathematic functions: add, subtract, multiply, square root, sine/cosign
- Logic: And, OR, exclusive OR
- Control functions: PID (Proportional Integral Derivative), Minimum, Maximum, Average
- Communications: Email, OPC UA, WEB Server, SMS, JSON.
Structured text (ST). Structured text provides a high-level procedural programming language with a syntax that resembles PASCAL, C, and C+ with complex statements and nested instructions supported. ST has many functions including iteration loops (REPEAT-UNTIL; WHILE-DO), conditional execution (IF-THEN-ELSE; CASE), and data arrays.
Sequential function chart (SFC). SFC enables the creation of threaded sequential and parallel control processing to define execution flow based on events and synchronized control operations (Figure 3). Control logic within an SFC block is created with any of the IEC 61131-3 programming methods.
Users can create their own functions in ladder logic, function block, and structured text to create logic and control that is encapsulated in a user created function block. The programmer can lock access to the application in the function block protecting intellectual property. This provides application engineers predefined and tested functions increasing quality and protects intellectual property.
More recently IEC 61131-3 functions can be created with other programming languages including C, C+, and Python.
Embedding intelligence in devices at the network “edge” where sensing and control are performed, is fundamental for the successful implementation of Industry 4.0 and Industrial Internet of Things (IIoT). This is being done today using standard IEC 61131-3 embedded runtime software.
Embedded intelligence at the network edge is imperative to achieve system response that satisfy the real-time requirements of flexible and agile manufacturing. Dramatic advances in hardware and software are making this practical and economical for a wide range of applications. There are several PLCopen member companies providing IEC 6 1131-3 solutions for embedded applications that run on system-on-a-chip, Raspberry Pi, and other edge processors. They can be found here.
No-code development platforms are essential for manufacturing and process subject matter experts to achieve the benefits of digital manufacturing in all of industry including discrete and process. IEC 61131-3 increases productivity, quality and profits. PLCopen is a worldwide organization with headquarters in the Netherlands with regional supporting offices in North America, Japan, China and Korea.
PLCopen has vendor certifications in several areas including those shown in Figure 4. A complete list can be found here.
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