The basic knowledge of programmable controller

PLC programmable controller is a kind of programmable memory, used for its internal storage procedures, to perform the logic operation, sequence control, timing, counting and arithmetic operations such as user-oriented instructions, and through the digital or analog input/output control various types of machinery or production process. Its full name in English Programmable Logic Controller, called Programmable Logic Controller, is defined as a kind of digital computing operations electronic system, specially designed for applications in industrial environment. DCS collecting and distributing SYSTEM: DCS English full name DISTRIBUTED CONTROL SYSTEM, is DISTRIBUTED CONTROL SYSTEM. DCS can be interpreted as the analog loop control is more widely used in industry, try to control the risk caused by the dispersed, and concentrate management and display functions of an automated high technology products. DCS generally consists of five parts: 1: the controller 2:3: the I/O board 4: operation station communication network 5: graphics and software. One, the development of PLC in the process of industrial production, a large number of switch quantity sequence control, it shall be carried out in accordance with the logical condition order movement, and according to the logic relation between chain protection action of control, and the amount of a large number of discrete data acquisition. Traditionally, these functions are realized through pneumatic or electric control system. In 1968 the United States GM ( General motors) Company instead of following the requirement of electric control device is put forward, in the second year, the United States digital company developed based on the integrated circuit and the control device of electronic technology, adopt programmatic approach is applied to the electrical control for the first time, this is the first generation of Programmable Controller, said Programmable Controller ( PC） 。 Personal computer ( Hereinafter referred to as PC) Development up, for the sake of convenience, also in order to reflect the functions and characteristics of the Programmable Controller, Programmable Controller called Programmable Logic Controller ( PLC） And now, still often will PLC or PC. In the 1980 s to mid - 90 - s, it is of the fastest growing period of PLC, the annual growth rate has maintained for 30 ~ 40%. PLC in this period, the ability to deal with analog and digital computing power, man-machine interface and network ability get improved, gradually into the field of process control of PLC controller, in some applications to replace the dominant in the field of process control in the DCS system. There are many kinds of definition of PLC. The international electrotechnical commission ( IEC） Is defined as the PLC programmable controller is a digital computing operation of electronic systems, specially designed for application in industrial environment. It USES a programmable memory, used in its internal storage to perform logical operations, sequential control, timing, counting and arithmetic operations such as instruction, and through digital and analog input and output, control various types of machinery or production process. Programmable controller and related equipment, should press easily and industrial control system to form a whole, easy to expand its function on the principle of design. PLC has strong commonality, easy to use, adaptation of wide, high reliability, strong anti-interference ability, simple programming and so on. The status of PLC in industrial automation control especially sequence control, in the foreseeable future, cannot be replaced. Second, the composition of PLC points from the structure, PLC is divided into fixed and modular ( Modular) Two kinds. Fixed PLC including CPU boards, I/O board, display panel, memory blocks, power supply, etc. , these elements are combined into a sealed, as a whole. Modular PLC, including CPU module, I/O module, memory, or the chassis, power supply module, these modules can be according to certain rules of combination configuration. Three, the constitution of the CPU, the CPU is the core of PLC, the nerve center of role, each PLC has at least one CPU, which is according to the function of the PLC system program to receive and store the user program and data, collected by scanning way by the state or data from input devices, and deposited in the register of regulations, at the same time, the diagnosis of the power and the working state of the circuit inside the PLC and programming in the process of grammatical errors, etc. Enter after the operation, to read a detailed instructions from the user program memory, after analyzing the task as stipulated in the instructions again to produce the corresponding control signal, to command the control circuit. Mainly by arithmetic unit, controller, CPU registers and their connections between data bus, control and state, CPU units include peripheral chips, bus interface and circuitry. Memory is mainly used to store programs and data, it is the indispensable component unit of PLC. In consumer point of view, unnecessary details the internal circuit of CPU, but due to the working mechanism of each part or enough understanding. CPU controller control CPU, which read instructions, explanation and executes instructions. But working rhythm by the shock signal control. Arithmetic unit used for digital or logic operations, work under the controller command. Register to participate in the operation, and store operations in the middle of the results, it is also the work under the controller command. CPU speed and memory capacity is one of the important parameters of the PLC, they determine the working speed of PLC, I/o number and software capacity etc. , thereby limiting the control scale. Four, the I/O module of PLC and the electric circuits of the interface, is through the input/output section ( I / O) The finished. I/O module integrates the PLC I/O circuit, its input register reflects the state of the input signal, the output points reflect the state of the output latch. Input module will be converted to digital signals into electrical signals, PLC controller system output module instead.
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