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The English name of the programmable controller is Programmable Controller,which has been referred to as PC for short in the 1970s and 1980s.Due to the development of personal computer in the 1990s,also referred to as PC;and the concept of programmable logic covers too much scope,so American AB Company named the programmable logic controller for the first time as programmable logic controller(PLC-Programmable Logic Controller),for the sake of convenience,PLC is still referred to as programmable logic controller.Some people call the system composed of programmable logic controllers PCS programmable control system,emphasizing that what programmable logic controller manufacturers provide to people is already a complete system.

Development and market situation of PLC

The development history of PLC

In 1968,the American GM(General Motors)Company proposed to replace the relay control device.In the following year,the American Digital Company developed the first-generation programmable logic controller,which met the requirements of GM’s assembly line.With the development of integrated circuit technology and computer technology,there are now the fifth generation of PLC products.

In the manufacturing industries characterized by changes in geometry and mechanical properties and the process industries characterized by physical and chemical changes that convert raw materials into products,in addition to feedback control based on continuous quantities,especially in the manufacturing industry,there are A large number of switch-based open-loop sequential control,which performs sequential action numbers according to logical conditions;in addition,there are chain protection actions independent of sequence and timing according to logical relationships;and a large number of switches,Pulse quantity,timing,counter,over-limit alarm of analog quantity and other state quantity-based data collection and monitoring of discrete quantity.Due to these control and monitoring requirements,PLC has developed into a product that replaces relay circuits and performs sequential control.In many years of production practice,PLC,DCS and IPC have gradually formed a three-legged situation,and other single-loop intelligent regulators occupy a certain percentage in the market.

From the 1980s to the mid-1990s,it was the period of the fastest development of PLC,and the annual growth rate has been maintained at 30~40%.Due to the progress of PLC connection processing simulation capabilities and network functions,it has squeezed a part of the DCS market(process control)and gradually monopolized industries such as sewage treatment.However,due to the emergence of industrial PC(IPC),especially in recent years,fieldbus technology In recent years,the growth rate of PLC has gradually slowed down.At present,there are more than 200 manufacturers around the world producing more than 300 varieties of PLC products,which are mainly used in automobiles(23%),food processing(16.4%),chemical/pharmaceutical(14.6%),metal/mining(11.5%),pulp/paper(11.3%)and other industries.