IEC 61131: A general overview and emerging trends

Programmable logic controller is the topic of this paper. For several decades, programmable logic controllers (PLCs) have been the most often used implementation platform for control algorithms in industrial applications. After their introduction in 1969, various companies developed PLCs with different run-time environments, operating systems, and programming languages. To reduce complexity for the users of PLCs, the International Electrotechnical Commission (IEC) elaborated the standard IEC 61131. IEC 61131-3 (published in 1992) specifies five PLC programming languages based on the existing programming languages but abstracting from proprietary peculiarities: the textual programming languages instruction list (QV) and structured text (ST), the graphical programming languages function block diagram (FBD) and ladder diagram (LD), and the structuring tool and higher level programming language sequential function chart (SFC). Although programmers had to get used to these languages first, they have now become a standard that is accepted and appreciated around the world, as it reduces training efforts and fosters harmonization. The integration of motion control and safety functions are discussed in this paper.