The development of PLC and its development trend

In the process of industrial production, a large number of switch quantity sequence control, it shall be carried out in accordance with the logical condition order movement, and according to the logic relation between chain protection action of control, and the amount of a large number of discrete data acquisition. Traditionally, these functions are realized through pneumatic or electric control system. In 1968 the United States GM ( General motors) Company instead of following the requirement of electric control device is put forward, in the second year, the United States digital company developed based on the technology of integrated circuit and electronic control unit, adopt programmatic approach is applied to the electrical control, generation of programmable controller, this is * says ProgrammableController ( PC） 。 The development of PLC and computer technology, semiconductor technology, control technology, digital technology, communication network technology such as higher is closely linked to the development of new technology. The development of high and new technology to promote the development of PLC and these high and new technology and the development of PLC to put forward higher and newer demands, promote the development of them. From the control function of PLC, PLC has experienced the following stages of development. From * by the mid - 1970 - s, the advent of PLC is the PLC of the start-up stage. Products are mainly used in the period of the PLC logic, timing, and counting, the PCU is composed of medium and small scale digital integrated circuit, its control function is more simple. From the mid to late 1970, is the practical application of PLC development stage. The period of the main control function of PLC products got greater development. With a variety of 8-bit microprocessor appeared, PLC technology leap. Because of the logical operation function, on the basis of increased the numerical calculation, closed loop adjusting function, improves the operation speed, expand the scale of the input/output. From the late 1970 s to the mid - 80 - s, is the realization of the function of PLC communication stage. With the development of computer communication, PLC also has the very big development in communication, initially formed the fraction of the communication network system. However, because each production manufacturer is fragmented, its own system, communication system so each production is more difficult to communicate with one another. In this phase, due to the need of production process control, greatly increase the demand for PLC, the features of the product has the development, the function of the mathematical operation got bigger expansion, to further improve product reliability. Since the mid - 1980 - s, is the opening stage of the PLC. PLC has strong commonality, easy to use, adaptation of wide, high reliability, strong anti-interference ability, simple programming and so on. The status of PLC in industrial automation control especially sequence control, in the foreseeable future, cannot be replaced. From the structure points, PLC is divided into fixed and modular ( Modular) Two kinds. Fixed PLC including CPU boards, I/O board, display panel, memory blocks, power supply, etc. , these elements are combined into a sealed, as a whole. Modular PLC, including CPU module, I/O module, memory, or the chassis, power supply module, these modules can be according to certain rules of combination configuration. Regarding the future trend of the development of PLC, mainly to miniaturization, specialty, low cost; Seriation, standardization, modular; High speed, large capacity and high performance processing; Networked direction.