PLC 40 years of development overview

In 1985, the International Electrotechnical Commission (IEC) defined the PLC as follows:
Programmable controller PLC is a digital computing operation of the electronic system, designed for industrial applications and design; it uses a class of programmable memory for its internal storage program, the implementation of logic operations, sequential control, timing, Counting and arithmetic operations and other operating instructions, and through digital, analog input, output, control of various types of machinery or production processes; programmable controllers and their peripherals are designed in accordance with the "easy to use and industrial control systems Together into a whole, easy to expand the functional principle ".
From the definition we can see: PLC is a kind of "prestored program" to determine the control function of industrial computer.
The 20th century, 60's, auto production line control system basically consists of relay control device. At that time, every modification of the car led directly to the redesign and installation of the relay control device. As production has progressed, vehicle model updates have become shorter, so that relay control devices need to be redesigned and installed frequently, which is time-consuming, labor-intensive, labor-intensive, and even hinders the shortening of the update cycle. In order to change this situation, General Motors Corporation in the United States in 1969 open tender, hoping to replace the relay control device with a new control device and put forward the following ten tender indicators:
(1) easy programming, the scene can be modified procedures;
(2) easy maintenance, modular structure;
(3) the reliability is higher than the relay control device;
(4) smaller than the relay control device;
(5) The data can be sent directly to the (superordinate) computer for management purposes;
(6) Cost can compete with the relay control device;
(7) Input can be AC 115V (Note: our China is AC220V);
(8) output (AC 115V, 2A above), can directly drive solenoid valves, contactors, etc .;
(9) In the expansion, the original system only need to make small changes;
(10) user program memory capacity can be expanded to at least 4KB.
In 1969, Digital Equipment Corporation (DEC) developed its first PLC and successfully tested it on a GM assembly line in the United States. This new type of industrial control device, with its small size, good variability, high reliability, long life, easy to understand, easy operation and maintenance and a series of advantages, and soon in many industries in the United States have been promoted. By 1971, it has been successfully used in food, beverage, metallurgy, papermaking and other industries.
The emergence of this new type of industrial control device has attracted the attention of many countries in the world. In 1971, Japan introduced the new technology from the United States and quickly developed their first PLC. In 1973, Western European countries also developed their first PLC. Our country began to develop from 1974 to 1977, applied to the field of industrial control.
Early PLC, generally known as "programmable logic controller" (Programmable Logic Controller). The PLC at this time is basically a (hard) replacement for the relay control device and is mainly used to realize the functions of sequential control, timing, counting and the like originally performed by the relay. It appears in the form of "quasi-computer" on the hardware and has been improved on the I / O interface circuit to meet the requirements of industrial control field. Devices in the device mainly uses discrete components and small and medium scale integrated circuits, and uses the core memory. In addition, some measures have been taken to improve anti-interference ability. In software programming, a method similar to the relay control circuit familiar to electrical engineers - the Ladder language is used. Therefore, the performance of the early PLC is better than the relay control device, which has the advantages of easy to understand, easy to install, small size, low energy consumption, fault display, can be reused. Which PLC-specific programming language - ladder language has been in use today.
The 20th century, 70's, the advent of microprocessors PLC changed dramatically. The United States, Japan, Germany and some other manufacturers have begun to use the microprocessor as a PLC CPU (Central Processing Unit), so that the function of PLC greatly enhanced. In software, in addition to maintaining the original logic operations, timing, counting and other functions, but also added arithmetic operations, data processing, network communications, self-diagnosis and other functions. In terms of hardware, in addition to maintaining the original switch module, an analog module, a remote I / O module, various special function modules are added, the memory capacity is expanded, and a certain number of data registers are also provided.
By the 20th century, 80 years, due to the rapid development of VLSI technology, microprocessor prices dropped significantly, making all types of PLC generally used by the microprocessor grade. Early PLC generally use 8-bit CPU, the current PLC generally uses 16-bit or 32-bit CPU. In addition, in order to further improve the processing speed of PLC, the manufacturers have also developed a dedicated logic processing chip, which makes the PLC hardware and software features have changed dramatically.
Currently, there are about 200 PLC manufacturers in the world. Among them, Rockwell, GE in the United States, Siemens in Germany, Schneider in France, Mitsubishi in Japan and Omron hold 80% More than the PLC market share, their products range from only a few dozen points (I / O total points) of the micro-PLC to 10,000 points giant PLC, everything.
After years of development, there are about 30 domestic PLC manufacturers, but not yet formed a considerable scale of production capacity, the domestic PLC application market is still dominated by foreign products, such as: Siemens S7-200 small series, S7-300 series , S7-400 series, Mitsubishi FX series, Q series, 0mron's CPM series, C200H series, and so on.
It is worth mentioning that, Hubei Huangshi Kewei Automation (www.kwzk.com) innovative products - "embedded PLC." Small system users want data processing like DCS, like PLC reliability, the price on the embedded microcontroller system. Embedded PLC just to meet these wishes of users. Embedded PLC refers to "embed the core EasyCore which supports PLC (ladder) programming language in the form of small board core into a specific control device, in addition to having its own special function, the device also has the basic PLC Function; developers in the PLC programming language platform, easy to design universal PLC, customer-based PLC, as well as a variety of special-shaped control panel. Embedded PLC is Kewei company based on the original automation instrumentation technology, field bus technology and more than 10 years of experience in automation projects in Huazhong University of Science and Technology, Wuhan University of Technology in collaboration, after three years of hard research, the first successful . As the embedded PLC's social and economic value is huge, in 2005 was classified as national research programs. So far, Kewei's embedded PLC products - Universal PLC, (in accordance with customer requirements) customer-based PLC, special-shaped control panel, has been in the textile machinery, industrial furnaces, plastic machinery, printing and packaging machinery, food Machinery, CNC machine tools, constant pressure water supply equipment, environmental protection equipment and other industries successfully applied, and in the application of the kiln automation system has obvious technical advantages.

For a long time, PLC has always been the protagonist of industrial automation, and DCS (Distributed Control System) and IPC (IPC) formed a three pillars of the trend. At the same time, PLC also suffered from the impact of other technology products, especially the impact of IPC. Miniaturization, networking, IPC, openness is the main direction of future development of PLC. PLC is still an infinite future.