Programmable Controller (PLC) is an industrial control device with rapid development and wide application in recent years. With the continuous development of PLC technology, in the field of automation design, the application scope of PLC technology is gradually expanding.
PLC has gone through more than 40 years of development and has been widely used all over the world. Introduction: Programmable Logic Controller (PLC) is a digital operation electronic system specially designed for application in industrial environment. It uses a programmable memory to store instructions for logic operation, sequence control, timing, counting and arithmetic operation. It controls various types of mechanical equipment or production process through digital or analog input and output. Nowadays, the ability of PLC in dealing with analog, digital operation, man-machine interface and network has been greatly improved, and it has become the mainstream control equipment in the field of industrial control, playing an increasingly important role in all walks of life. In 2001, in order to meet the industrial needs of the continuous updating of automotive models, General Motors of the United States tried to develop a method of redesigning relay control circuits on automotive assembly lines to minimize changes in automotive models. In 1969, the United States Digital Equipment Corporation (DEC) developed the world’s first programmable logic controller (PLC). In 1971, Japan introduced and digested PLC technology from the United States, and successfully developed Japan’s first PLC. Early programmable logic controllers were generally called programmable logic controllers. At this time, PLC has the meaning of substitutes for relay control devices, its main function is only to perform the sequence control timing previously completed by relays, etc.
In the mid-term of PLC software, besides maintaining its original logic operation, timing, counting and other functions, it also adds arithmetic operation, data processing and transmission, communication. Self-diagnosis and other functions. In terms of hardware, besides maintaining its original switch module, analog module, remote I/O module and various special function modules are also added. Recently, PLC came into use in the mid and late 1980s. Because of the rapid development of VLSI technology, the market price of microprocessors has dropped dramatically, which makes various types of PLCs adopt.
At the same time, microprocessors have been generally improved, and manufacturers have developed special logic processing chips. In this way, the software and hardware functions of PLC have undergone tremendous changes. With the development of PLC, a series of large, medium and small scale products have been formed. It can be used in various industrial control occasions. In addition to the logic processing function, most modern PLCs have perfect data operation ability, which can be used in various digital control fields. In recent years, a large number of functional units of PLC have emerged, which makes PLC permeate into various industrial controls such as position control, temperature control, CNC and so on. With the enhancement of communication ability of PLC and the development of man-machine interface technology, it is very easy to use PLC to form various control systems. Because of its own characteristics and advantages, PLC has been widely used in industrial control. You have been applied in many fields, such as machinery, metallurgy, chemical industry, electricity, transportation and construction. Its application scope is roughly between relay control device and industrial process control computer. It is suitable for complex control function requirements, input and transmission. Where there are more points. In the control of single equipment, it can also be used for multi-computer group control and automation pipeline. In the process of industrial production, there are some continuous variables such as temperature, pressure, flow rate, liquid level and velocity (i.e. analog variables), which are processed by corresponding A/D and D/A conversion modules and various control algorithm programs to complete closed-loop control. Adjustment is one of the most widely used methods in general closed-loop control systems. Process control is widely used in metallurgy, chemical industry, heat treatment and boiler control. In manufacturing industry, there are a large number of open-loop sequential control with switching quantity as the main variable, thermostatic element which operates sequentially according to logical conditions; in addition, there are control of interlocking protection action in accordance with logical relationship which is independent of sequence and sequence; and a large number of switching quantity, pulse quantity, timing, counter and analog quantity. Data acquisition and monitoring of discrete variables is the main state variables such as over-limit alarm. Because of these control and monitoring requirements, PLC has developed into a product that replaces relay circuit and carries out sequential control. PLC manufacturers have gradually increased various communication interfaces on the original CPU template.
Fieldbus technology and Ethernet technology have also developed synchronously, making the application of PLC more and more widely. PLC has the advantages of stability, reliability, low price, complete functions, flexible application and convenient operation and maintenance, which is the fundamental reason why it can occupy the market for a long time.
The 32-bit microprocessor has the functions of networking communication, data operation and data information transmission for multiple daily signs and tasks at the same time. With the increase of running speed, the storage capacity of the microprocessor is also increasing, which also enhances the ability of process control and operation. In order to realize the information management letter of enterprises, the microprocessor has the function of networking communication. Information technology has also penetrated into the industrial PLC control technology. High reliability is the key performance of electrical control equipment. PLC is manufactured by modern large scale integrated circuit technology and strict production process. The internal circuit adopts advanced anti-interference technology, which has high reliability. In addition, the PLC has the function of hardware fault self-detection, which can send out alarm information in time when a fault occurs.
In the application software, the applicant can also program the fault self-diagnosis program of peripheral devices, so that the circuit and equipment in the system besides PLC can also get fault self-diagnosis protection. As an important part of automation control network and international general network, PLC plays an increasingly important role in many fields outside industry and industry.