1 Introduction Programmable Logic Controller English as ProgrammableController, 70-80 years in the twentieth century has been referred to as the PC. As the 90's, personal computers developed, also referred to as the PC; plus programmable large area covered by the concept, so the first time the U.S. AB, named PLC programmable logic controller (PLC -ProgrammableLogicController), for convenience, is still referred to as programmable logic controller PLC. It was composed of the PLC programmable control system known as the PCS system, stressed the PLC manufacturer provides to the people is a complete system.
2 PLC development and market conditions History of the development
2.1 PLC 1968 U.S. GM (General Motors) Company to replace the relay control device requirements, the second number of companies in the United States developed the first generation of programmable logic controller, to meet the requirements of the GM assembly line company. As the IC technology and computer technology, now the fifth generation PLC product.
In to change the geometry and mechanical performance of the manufacturing industry and is characterized by physical and chemical changes in raw materials into products will be characterized by the process industry, in addition to a continuous volume-based feedback control, particularly in the manufacturing industry exist a large number of binary-based open-loop sequence control, it logical conditions in the temporal order of action No. Action; plus with the order, timing relationship between the independent chain of protection in accordance with the logic controlling the motion; and large switching volume, pulse volume, timing, counters, analog alarm state, the more limited amount of mainly? discrete data collection and monitoring. These control and monitoring requirements, replace the relay PLC developed into a sequential control circuit and the main products. After years of production practice, gradually formed a PLC, DCS and the three pillars of the IPC.
In the mid 80s to 90, is the PLC of the fastest growing period, has maintained an annual growth rate of 30 ~ 40%. As the PLC machine simulation capabilities and Handling of network functions and progress, diverts part of the DCS in the market (process control) and a gradual monopolization of the sewage treatment industry, but because of the industrial PC (IPC) appearance, especially in recent years, Fieldbus Technology development, IPC and PLC FCS also occupied the part of the market, the growth rate of PLC in recent years, the total is gradually slowed. Currently there are more than 200 manufacturers around the world more than 300 varieties of PLC products, mainly used in cars (23%), food processing (16.4%), chemical / pharmaceutical (14.6%), metal / mining (11.5%), pulp / create paper (11.3%) and other industries.
2.2 PLC market conditions Domestic PLC plant about 30, but did not form a full-scale production capacity and brand-name products, and partly by imitation, contract assembly, or "OEM" means of production, it can be said that our country is not formed in the manufacture of PLC industry. As the principles, techniques and processes had no difficulty cutting-edge technology products, as long as the effort is to form a manufacturing industry.
PLC application in China is very active in recent years, annual investment of about 100,000 sets of the new PLC products, with annual sales of 3 billion yuan, the industry is very broad application. But compared with other countries, in the mechanical aspects of processing and production line applications, also need to increase investment. China's market, there are several popular PLC products:
(1) Schneider, including the early introduction of Tianjin Instrument Factory Modicon products, there are Quantum, Premium, Momentum, etc.;
(2) Rockwell (including AB company) PLC products, there are SLC, MicroLogix, Control Logix, etc.;
(3) Siemens products are currently SIMATIC S7-400/300/200 products;
(4) GE products; Japan, Omron, Mitsubishi, Fuji, Panasonic and other products.
PLC's market potential is enormous, not only in our country, even in industry, Japan has developed survey, PLC's mechanical and electrical integration products matching the proportion of 42%, using relays, contactor control 24% still . Therefore, the need to apply the PLC are still many occasions in our country even more so.
From the perspective of technological innovation, China's large and medium enterprises should also develop CIMS (Computer Integrated Manufacturing System), in the machinery factory to form FMS flexible manufacturing system, PLC is the foundation, the PLC market is vast.
PLC with stable, reliable, cheap, functional, application flexibility, convenient operation and maintenance advantages, this is it sustained the root causes of market share, we are following highlights several issues, and to study its development trend.
3 PLC hardware and software 3.1 PLC Classification PLC has been formed in the 90's micro, small, medium, large, large variety of PLC. By I / O points points, can be divided into:
* Micro PLC: 32 I / O * Small PLC: 256 I / O * Medium PLC: 1024 I / O * Large PLC: 4096 I / O
* Giant PLC: 8195 I / O I am Chinese Manufacturers writer, reports some information about cast iron trivets , jerry can spout.
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