PLC's domestic and international situation and future prospects
In the industrial production process, a lot of switching sequence control, which in accordance with the conditions of the order to move a logical and controlled chain protection action in accordance with the logic of relations, and a large number of discrete data collection. Traditionally, these functions are controlled by pneumatic or electrical input output module plc system to achieve. 1968 American GM (General Motors) companies to replace the electrical control device, following the requirements of the second year, the United States Digital Equipment Corporation (DEC) developed a control device based on the integrated circuit and electronics technology, first applied to adopt procedural means electrical control, this is the first generation of programmable logic controller, called plc digital io module Programmable, is recognized as the world's first PLC. Limited to the level of development of computer components and conditions at the time, early PLC discrete components mainly composed of small and medium-scale integrated circuits that can perform simple logic control and timing, counting function. 20 in the early 1970s there has been a microprocessor. It will soon be introduced into the programmable controller, so that PLC increased computing, data transmission and processing functions, complete with real industrial control devices computer features. In order to facilitate the familiar relays, contactors systems engineering and technical personnel, and the relay circuit programmable controller uses a similar ladder as the main programming language, and will participate in computing and computer storage elements are processed to relay name. At this point the PLC to computer technology and the concept of combining conventional control relay product. After a personal computer (referred to as PC) to develop, in order to facilitate, but also to reflect the features of programmable controllers, programmable logic controller named Programmable Logic Controller (PLC).