PLC arises at the historic moment because of the need of industrial automation control system. After decades of development, it has been widely used in industrial equipment. Through the research and application of PLC, we can develop a better industrial automation control system, so as to ensure the smooth operation of production. Before the advent of Programmable Logic Controller (PLC), relay control dominated the field of industrial control. Relay control system has obvious shortcomings: large size, thermostatic element high power consumption, poor reliability, short life, slow operation speed, poor adaptability. Especially when the production process changes, it must be redesigned and installed, resulting in a serious waste of time and money. In order to change this situation, General Motors, the largest automobile manufacturer in the United States, in 1968, in order to meet the requirement of constantly updating automotive models and occupy sufficient advantages in the fiercely competitive automotive industry, proposed to develop a new type of industrial control device to replace relay control device. Therefore, it made a special public offer. Mark. According to the request of bidding, in 1969, American Digital Equipment Company developed the first programmable logic controller in the world, and tried it on the automatic assembly line of General Motors Company. It was successful, thus creating a new era of industrial control.
Since then, the new control technology of PLC has developed rapidly, and it has developed rapidly in the developed industrial countries. Since the birth of the first PLC, there are roughly four courses. In the first generation, one-bit computer is widely used for development, and magnetic core memory is used for storage, which simply implements the logic control function. In the second generation, 8-bit microprocessors and semiconductor memory were used, and the products were serialized. In the third generation, high performance microprocessors and bit chip processors are used, which greatly improves the computing speed, thus promoting the development of multifunctional and networked communications. The fourth generation not only uses high performance and high speed processors such as 16-bit, 32-bit microprocessors, bit-chip microprocessors and streamlined instruction system microprocessors, but also configures multiple microprocessors in a programmable controller at the same time, which greatly improves its performance, operation speed and calculation accuracy. At the same time, due to the emergence of a large number of intelligent modules containing microprocessors, it has many functions, such as logic control, process control, motion control, data processing, networked communication and so on. It has become a real multi-functional controller. At present, with the development of micro-electronics technology, such as large-scale and ultra-large-scale integrated circuits, PLC has developed from the first computer to a microprocessor consisting of 16-bit and 32-bit microprocessors, and realized multi-channel processing of multiprocessors. Now, the technology of PLC is very mature. It not only enhances the control function, reduces the power consumption and volume, reduces the cost, enhances the reliability, but also makes programming and fault detection more convenient. At the same time, with the development of remote control and communication network, data calculation and image processing, programmable logic controller (PLC) has been used in continuous production control and has become a pillar of industrial production automation. Now, there are more than 200 PLC manufacturers in the world, and more than 400 kinds of PLC products, which can be divided into three series products by region, namely, the United States, Europe and Japan. Each series of products has its own characteristics. Among them, the United States is a major producer of PLC, there are more than 100 manufacturers, well-known A-B company, General Electric Company, Modican Company. The main producers of European products are Germany’s Siemens, AEG and France’s TE. Japan’s Mitsubishi, Omron, Panasonic, Fuji and so on. Samsung, LG, etc.
These manufacturers account for most of the market. The research and application of PLC in China began in the mid-1970s.
Research began in 1974, but it was not extended due to the limitations of production level and components. In 1977, a microprocessor-based PLC was developed and applied in industrial production.
At the end of 1970s, due to the importation of complete sets of special equipment from abroad, China introduced many foreign products. At the same time, the application of PLC was gradually increased in the equipment transformation and design, and good results were achieved.
Many scientific research institutes and high-tech enterprises, while actively introducing foreign programmable logic controller equipment, digest, absorb and inherit the development, redevelop and develop some of our own brand of programmable logic controller. After years of development, there are about 30 domestic PLC brands. But most of the domestic PLCs are foreign brands.
This shows that domestic PLC is also facing great technological innovation and market competition pressure. With the increasing application of PLC, the technology of PLC and its product structure are constantly upgraded and transformed, the functions are constantly increasing, and the cost-effective ratio is getting higher and higher. In terms of product size. On the one hand, in order to meet the needs of single-chip computer and small-scale control system, vigorously develop small and ultra-small PLCs with fast operation speed and low price. On the other hand, with the complexity of system control, the requirement of fast computing speed must also meet the needs of users with large storage capacity. This determines the high-speed and large-scale development of PLC. Develop to network. Networking has become the trend of PLC development in the future. The networking communication between PLC and PLC, and between PLC and PC has been widely used in practice. At present, every manufacturer is trying to study the communication technology of its own products. At the same time, different manufacturers are also negotiating designated communication standards to form a larger network system to facilitate the development and control of the system. PLC has become an indispensable part of DCS. Develop to modularization and intellectualization. In order to meet the changeable and flexible requirements of industrial automation control system. PLC researchers have developed various functional modules, such as intelligent I/O control module, temperature control module and module specially used for fault detection. These powerful modules provide great convenience for the development and application of the system.
Diversification and standardization of programming languages and software. At present, each brand of PLC products has its own programming language, programming software, showing a parallel trend. In the future, PLC will develop slowly to the manufacturing automation protocol, which will make the basic hardware, software and software development tools of PLC more standardized and unified. Because of the remarkable advantages of programmable logic controller, it has been highly concerned by the world since its birth. During the growth of programmable logic controller for more than 30 years, the production of programmable logic controller has developed into a huge industry. According to incomplete statistics, there are more than 200 manufacturers of programmable logic controllers and their control networks in the world, and more than 400 kinds of products are produced. The output and sales of programmable logic controller (PLC) have always been the highest in industrial control equipment. So far, world market demand for it is still rising steadily.