A Programmable Logic Controller (PLC) is a universal industrial automatic control device developed based on microprocessors, integrating computer technology, automatic control technology, and communication technology [13]. It uses programmable memory as the internal instruction memory device and has functions such as logic, sequencing, timing, counting, and arithmetic operations. [13]
The core of a PLC consists of a central processing unit, memory, input/output modules, and communication interfaces [1-3], supporting various programming languages such as ladder diagrams and function block diagrams, and is widely used in automotive manufacturing, energy and chemical industries, and mechanical processing, etc. [2] [6] [10] [12]. According to its composition structure, it can be divided into integrated PLC and modular PLC [13]. It has the characteristics of high reliability, strong anti-interference ability, variable control programs, and good flexibility [13]. It was developed based on relay-contactor control. In 1969, the American Digital Equipment Corporation developed the first programmable logic controller [13]. Since then, this new type of industrial control device has been quickly promoted and applied in other industrial fields in the United States [13]. In 1971, Japan introduced this new technology and began to produce programmable logic controllers [13]. In 1973, Western European countries also began to develop and produce programmable logic controllers [13]. In 1974, China began to develop programmable logic controllers and started to apply them in industrial production [13]. In the early 1980s, it has been widely used in advanced industrial countries [5]. From the 1980s to the mid-1990s, it was the fastest-growing period [5]. In the late 20th century, it was more suitable for the needs of modern industry [5]. In the 21st century, with the promotion and implementation of the IEC61131 series standards, especially the IEC61131-3 programming language standard, PLC has entered the era of openness and standardization. [14]
With the development of modern science and technology, PLC is not only used for sequential logic control, but can also receive various digital signals and analog signals, perform logical operations, function operations, and floating-point operations, etc. [13], and is one of the three pillars of modern industrial automation.