Programmable controller is a member of computer family, which is designed and manufactured for industrial control applications. The early programmable controller is called programmable logic controller (PLC), which is mainly used to replace relay to realize logic control. With the development of technology, the function of this device has greatly exceeded the scope of logical control, so today this device is called programmable controller, or PC for short. But in order to avoid confusion with the abbreviation of personal computer, programmable controller is called PLC for short. PLC is a kind of digital operation electronic equipment specially designed for industrial environment application. It uses programmable memory to store instructions for performing logical operations, sequential operations, timing, counting and arithmetic operations, and can control various types of machines or production processes through digital or analog input and output. PLC and its related peripheral equipment should be designed according to the principle that it is easy to form a whole with industrial control system and expand its functions. Features of PLC: 1 High reliability and strong anti-interference ability. 2 complete hardware, perfect function and strong applicability. 3. easy to learn and use. 4. The design, installation and debugging of the system have small workload, convenient maintenance and easy transformation. 5. Small size, light weight and low energy consumption. 1. The development trend of contemporary PLC technology is rapid development and product upgrading. Develop various intelligent modules to continuously enhance process functions; The combination of PLC and PC; The communication networking function has been continuously enhanced; Develop new programming languages to enhance fault tolerance. Second, the development trend of contemporary PLC technology. General Motors Corporation of the United States put forward ten conditions for a new generation of controllers as users. These ten conditions are: 1. Convenient programming, can modify the program on site; 2. Easy maintenance, preferably plug-in; 3. The reliability is higher than that of relay control cabinet; 4. The volume is smaller than the relay control cabinet; 5. Data can be sent directly to the management computer; 6. It can compete with relay control in cost; 7. The input can be AC115v; 8. The output is above AC 1 15V/2A, and the solenoid valve can be directly driven; 9. When expanding, the original system only needs to be slightly changed; 10. The storage capacity of the user program can be extended to at least 4K bytes. There are many programming languages of programmable controller PLC, including ladder diagram language, Boolean mnemonic language, function diagram language, function module diagram language and structured statement description language. At present, the supply of PLC application talents mainly depends on universities (267 related majors), higher vocational colleges (more than 600) and technical schools (more than 2,000). Its related majors are generally called automation, mechanical manufacturing and its automation, electrical automation and mechatronics. 2 1 century, PLC will have greater development. Technically, the new achievements of computer technology will be more applied to the design and manufacture of programmable controllers, and there will be varieties with faster operation speed, larger storage capacity and stronger intelligence; From the perspective of product scale, it will further develop in the direction of ultra-small and ultra-large; From the perspective of product compatibility, the varieties and specifications of products will be more abundant, and the perfect man-machine interface and complete communication equipment will better meet the needs of various industrial control occasions; From the market point of view, the situation that each country produces a variety of products will be broken with the intensification of international competition, and there will be a situation that a few brands monopolize the international market, and there will be an internationally common programming language; From the development of network, it is the development direction of programmable controller technology to connect programmable controller with other industrial control computers to form a large-scale control system. At present, a large number of programmable controllers have been applied to computer DCS (distributed control system). With the development of computer network, programmable controller, as an important part of automation control network and international general network, will play an increasingly important role in many fields other than industry.

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