Programmable Logic Controller (PLC), abbreviated as PLC, is a new type of industrial control device developed based on microprocessors and integrating computer technology, automatic control technology, and communication technology. It has the advantages of simple structure, convenient programming, and high reliability, and has been widely used in automatic control of industrial processes and positions. According to statistics, programmable controllers are the most commonly used equipment in industrial automation devices. Experts believe that programmable controllers will become the main means and important basic equipment for industrial control in the future. PLC, robots, and CAD/CAM will become the three pillars of industrial production.

PLC is continuously developed and improved by combining relay control logic with 3C (Computer, Control, Communication) technology. At present, it has developed from small-scale single machine sequential control to all control fields including process control, position control, and other occasions.

The various types of PLCs used in automation systems, some are centrally installed in control rooms, while others are dispersed and installed on individual equipment in production sites. Although they are mostly located in harsh electromagnetic environments formed by strong electrical circuits and equipment, PLCs are control devices specifically designed for industrial production environments. In the design and manufacturing process, multi-level anti-interference and component selection measures are adopted, so they have strong adaptability to harsh industrial environments, operational stability, and high reliability. Therefore, they generally do not require any special measures to be taken and can be directly used in industrial environments.

High reliability is a key performance of electrical control equipment. Due to the use of modern large-scale integrated circuit technology and strict production processes, PLC has high reliability with advanced anti-interference technology for its internal circuits. For example, the F-series PLC produced by Mitsubishi Corporation has an average processing time of up to 300000 hours. The average working time of some PLCs using redundant CPUs is longer. From the perspective of the external circuit of PLC, using PLC to form a control system, compared with relay contactor systems of the same scale, the electrical wiring and switch contacts have been reduced by hundreds or even thousands, and faults have been greatly reduced. In addition, the PLC has a hardware fault self detection function, which can promptly issue alarm information when a fault occurs. In application software, users can also incorporate fault self diagnosis programs for peripheral devices, enabling circuits and equipment in the system other than PLCs to also receive fault self diagnosis protection. It is not surprising that the entire system has * reliability.