1. In manufacturing industry (characterized by changing geometry and mechanical properties) and process industry (characterized by transforming raw materials into products through physical and chemical changes), a large number of switches are controlled in sequence, which perform sequential actions according to logical conditions, control interlock protection actions according to logical relations, and collect a large number of discrete data. Traditionally, these functions are realized by pneumatic or electric control systems. 1968 American GM (general motors) company proposed to replace the electronic control device. In the second year, American digital company developed a control device based on integrated circuit and electronic technology, which programmed the electrical control function. This is the first generation of programmable controller, and its English name is Programmable Controller(PC).
2. With the emergence of electronic technology and computer technology, the function of PC is becoming more and more powerful, and its concept and connotation are also expanding.
In 1980s, personal computer was developed, also called PC for short. In order to facilitate and embody the functional characteristics of the programmable controller, A-B Company of the United States named it Programmable Logic Controller (PLC) and took "PLC" as the registered trademark of its products. Now, PLC is usually referred to as PC for short.
4. From 1980s to the mid-1990s, PLC developed the fastest, with an annual growth rate of 30-40%. During this period, the analog processing ability, digital computing ability, man-machine interface ability and network ability of PLC have been greatly improved, and PLC has gradually entered the field of process control, replacing DCS system, which is dominant in the field of process control, in some applications.
5. In recent years, industrial computer technology (IPC) and field bus technology (FCS) have developed rapidly, occupying a part of the PLC market, and the growth rate of PLC has gradually slowed down, but its position in industrial automation control, especially in sequence control, cannot be replaced in the foreseeable future.
6. At present, there are more than 200 manufacturers in the world producing more than 300 kinds of PLC products, which are mainly used in automobiles (23%), grain processing (16.4%), chemistry/pharmacy (14.6%) and metals/mines (1/kloc-0).
Second, the typical PLC products
1, abroad
Schneider company, quantum, premium, momentum, etc.
Rockwell (A-B Company), SLC, MicroLogix, Control Logix, etc.
Siemens, SIMATIC S7-400/300/200 series;
ge
Japan Omron, Mitsubishi, Fuji, Panasonic, etc.
2. Domestic
There are about 30 PLC factories, but there are no large-scale production capacity and brand-name products, and some of them are produced by imitation, component assembly or OEM.
Third, the application of PLC in China
Although our country is very weak in PLC production, it is very active in PLC application. In recent years, about 654.38 million sets of PLC products have been added every year, with an annual sales of 3 billion RMB, and the application industry is also very extensive.
At home, PLC is generally divided into the following levels according to I/O (but not absolutely, there are some differences in classification abroad):
Micro:? 32 inputs/outputs
Small: 256 I/O.
Medium:1024 I/O.
Large: 4096 I/O
Giant: 8 192 input/output
In the PLC system applied in China, the sales of PLC with I/O below 64 points account for 47% of the whole PLC, and those between 64 points and 256 points account for 365,438+0%, accounting for 78% of the whole PLC sales.
The PLC applied in China covers almost all brands in the world, showing the trend of the Eight-Power Alliance, but it has its own sphere of influence in the industry. Most large and medium-sized centralized control systems use European and American PLC, while most small control systems, machine tools, stand-alone automation and OEM products use Japanese PLC. European and American PLC has advantages in network and software, while Japanese PLC has advantages in flexibility and price.
The supply channels of China PLC mainly include manufacturers, distributors (agents), system integrators, OEM users and end users. Among them, most PLCs reach the end users through distributors and system integrators.
Fourth, the focus of PLC development
1, the man-machine interface is more friendly.
PLC manufacturers have greatly improved their software level by acquiring or merging software enterprises or developing software industry. Most PLC brands have corresponding development platforms and configuration software. The combination of software and hardware improves the performance of the system, reduces the development and maintenance costs of users, and makes it easier to form a man-machine friendly control system. At present, the mode of PLC+ network +IPC+CRT is widely used.
2. The network communication ability has been greatly enhanced.
On the basis of providing physical interface RS232/422/485 on the original CPU template, PLC manufacturers gradually increased various communication interfaces and provided a complete communication network. Due to the rapid development of data communication technology in recent years, users have a strong demand for openness, and fieldbus technology and Ethernet technology have also developed simultaneously. For example, the three-layer network structure system introduced by Rockwell A-B Company, namely Ethernet, control network and equipment network, and the Profibus-DP and Profibus-FMS networks of Siemens Company.
3. Openness and interoperability have made great progress.
In the development process of PLC, in order to monopolize and expand its own market, PLC manufacturers are in a situation of independent rule, and each has its own standards, which brings inconvenience to users and increases maintenance costs. Opening up is the trend of development, which has been recognized by manufacturers, forming a long-term process of compromise and competition, and this process is still going on. The opening process can be reflected in the following aspects:
1)IEC has formed a fieldbus standard, which includes eight standards. Although some people say that many standards have no standards, this is the result of difficult arguments and compromises. After the introduction of standards, manufacturers have adapted their products to these standards or developed new products corresponding to them.
2)IEC has formulated the Windows-based programming language standard IEC 611-3, which specifies five programming languages: instruction list (IL), ladder diagram (LD), sequential function diagram (SFC), functional block diagram (FBD) and structured text (st). This is a standardized document that is open to the programmable logic control device based on digital technology at a high level. Although the tools developed by PLC are still incompatible, the development system based on these standards makes it easier for users to adapt to different brands of products in the application process.
3)OPC Foundation proposed OPC(OLE for Process Control) standard, which further enhanced the interoperability between software and hardware. Through OPC conformance testing products, convenient and seamless data exchange can be realized. At present, most PLC software products and a considerable number of instruments, actuators and other equipment have OPC function. The combination of OPC technology and fieldbus technology is the development trend of FCS technology in the future control system.
4. The function of 4.PLC is further enhanced, and its application scope is more and more extensive. The network ability, analog processing ability, operation speed, memory and complex operation ability of PLC have been greatly enhanced, and it is no longer limited to the application of logic control, but is increasingly used in process control. According to statistics, PLC has functional applications in some fields except petrochemical process, and has replaced expensive DCS in quite a few applications, thus changing the original PLC (sequence control) +DCS (process control) mode into PLC+IPC mode.
5. The development of industrial Ethernet has an important impact on PLC. Ethernet is widely used, and its cost is very low compared with industrial networks. Therefore, people are committed to introducing Ethernet into the control field. At present, the challenge is that 1) hardware should be suitable for harsh industrial environment; 2) How to improve the reliability of communication mechanism. Whether Ethernet can successfully enter the field of industrial control is still controversial. However, the application of Ethernet in industrial control system is increasing. In order to adapt to this process, various PLC manufacturers have introduced products or intermediate products that adapt to Ethernet.