The development of production technology requirements of the American automobile industry promoted the emergence of PLC. In the 1960s, when General Motors adjusted the factory production line, it found that the relay and contactor control systems were difficult to modify, large in size, noisy, inconvenient to maintain and had poor reliability, so it proposed the famous "General Ten" bidding indicators.
In 1969, the American Digital Equipment Company developed the first programmable controller (PDP-14), which was tested on the production line of General Motors and achieved remarkable results; in 1971, Japan developed the first programmable controller (DCS-8); in 1973, Germany developed the first programmable controller; in 1974, China began to develop programmable controllers: in 1977, China promoted PLC in industrial applications.
The original purpose was to replace mechanical switching devices (relay modules). However, since 1968, the functions of PLC have gradually replaced relay control boards, and modern PLCs have more functions. Its use extends from single process control to the control and monitoring of the entire manufacturing system.
Microprocessors appeared in the early 1970s. People soon introduced it into programmable logic controllers, which added functions such as calculation, data transmission and processing to programmable logic controllers, completing industrial control devices with real computer characteristics. At this time, programmable logic controllers were the product of the combination of microcomputer technology and conventional relay control concepts. After the development of personal computers, in order to facilitate and reflect the functional characteristics of programmable logic controllers, programmable logic controllers were named Programmable Logic Controllers (PLC).
In the mid-to-late 1970s, programmable logic controllers entered the practical development stage, and computer technology was fully introduced into programmable controllers, making their functions leap forward. Higher computing speed, ultra-small size, more reliable industrial anti-interference design, analog quantity calculation, PID function and extremely high cost performance have established its position in modern industry.
In the early 1980s, programmable logic controllers have been widely used in advanced industrial countries. The number of countries producing programmable controllers in the world is increasing, and the output is increasing. This marks that programmable controllers have entered a mature stage.
From the 1980s to the mid-1990s, programmable logic controllers developed fastest, with an annual growth rate of 30~40%. During this period, the PLC's ability to process analog quantities, digital computing capabilities, human-machine interface capabilities, and network capabilities have been greatly improved. Programmable logic controllers have gradually entered the field of process control, and in some applications have replaced the DCS system that dominates the field of process control.
In the late 20th century, the development of programmable logic controllers was characterized by being more adapted to the needs of modern industry. During this period, large and ultra-small computers were developed, various special function units were born, and various human-machine interface units and communication units were produced, making it easier to match industrial control equipment using programmable logic controllers.
