Introduction of the development of PLC for 40 years

In 1985, the international electrotechnical commission ( IEC) Definition is as follows: to PLC programmable controller PLC is a kind of digital computing operations electronic systems, specially designed for applications in industrial environment; It USES a programmable memory for its internal storage procedures, to perform logic made operations, sequential control, timing, counting and arithmetic operations such as instruction, and through digital, analog input, output, control various types of machinery or production process; The design of the programmable controller and related peripheral equipment, should be in accordance with the 'easy got behind with the industrial control system, easy to extend the functionality of a whole principle'. By this definition: PLC is a kind of controlled by the 'storage program in advance' to determine the function of industrial control computer. In the 1960 s, auto production line automatic control system is basically composed of relay control device. When car every retrofit led directly to the redesign and installation of relay control device. With the development of production, vehicle model update cycle shorter, thus relay control device will need to frequently redesign and installation, it is not only time-consuming, work, material, or even hindered the update cycle shortened. In order to change this situation, the American general motors in 1969, public bidding, hope with the new control device to replace the relay control device, and put forward the following 10 measures of bidding: 1) programming is convenient, the scene can modify the program; (2) convenient maintenance, adopting the modular structure; (3) the reliability is higher than the relay control device; (4) volume is less than the relay control device; 5. Data can be directly into a management role, Upper) The computer; [6] cost with relay control device competition; Once the input can be ac 115 v ( Note: we are China AC220V) ； Being output for ( Ac 115 v, 2 a) above , can direct drive solenoid valve, contactor, etc; When 'levies in extension, the original system only requires a small changes; ⑽ at least could extend to the user program memory capacity of 4 KB. In 1969, the United States, digital equipment corporation ( 12月) Developed the first PLC, and general motors automatic assembly line in the United States to begin testing, a success. This new type of industrial control device, with its small volume, good variability, high reliability, long service life, simple and convenient operation and maintenance and a series of advantages, soon is widely used in many industries in the United States. In 1971, has been successfully applied in food, beverage, metallurgy, paper and other industries. The emergence of a new type of industrial control device, attaches great importance to by many countries in the world. In 1971, introduced the new technology from the United States, Japan, quickly developed their 1 sets of PLC. In 1973, western European countries have developed their 1 PLC. Our country developed from 1974 to 1977 began to application in the field of industrial control. The early PLC, commonly known as 'programmable logic controller' ( 可编程逻辑控制器) 。 At this time of the PLC is basically ( Hard) A substitute relay control device, is mainly used to achieve the original completed by relay sequential control, timing, counting and other functions. It on the hardware in the form of 'computer', in the I/O interface circuit for improved to adapt to the industrial control field requirements. Device in the device mainly adopts discrete component and small and medium scale integrated circuit, and USES the core memory. In addition, also took some measures to improve the anti-interference ability. On the software programming, by using the similar to electrical engineers are familiar with the relay control circuit of the way - — Ladder diagram ( 梯) Language. Therefore, the early PLC is superior to the performance of relay control device, its advantage is easy to understand, easy to install, small volume, low energy consumption, such as fault display, can repeat use. Characteristic of PLC programming language - — Ladder diagram language has been in use today. In the 1970 s, the appearance of the microprocessor PLC have changed dramatically. The United States, Japan, Germany and some other manufacturers have started using microprocessor as the PLC CPU ( The central processing unit) So that make the function of PLC is greatly enhanced. On the software side, in addition to keep the original logic made operation, timing, counting, and other functions, also increased the arithmetic, data processing, network communications, such as self-diagnosis function. In terms of hardware, in addition to keep the original switch module, also increased the analog module, remote I/O module, various special function module, and expand the capacity of storage, but also provide a certain amount of data register. In the 20th century in 80, due to the rapid development of very large scale integrated circuit technology, the microprocessor prices fell sharply, making various types of PLC used in the class of the microprocessor general improvement. Early PLC generally adopt 8-bit CPU, now commonly used PLC 16 or 32 bit CPU. In addition, in order to further improve the processing speed of PLC, the factory also have developed a special logic processing chip, this makes the PLC hardware and software function is the change. At present, some 200 PLC manufacturers in the world, among them, the American Rockwell, GE, Siemens of Germany, Siemens) , France schneider ( Schneider) , Japan's mitsubishi, omron, Omron) , they control the PLC market share of more than 80% of the world, their series products from only a few dozen points ( Total points I/O) Miniature PLC to have tens of thousands of giant PLC, over everything.