可編程邏輯控制器(programmable logic controller,plc)（可編程邏輯控制器（可編程邏輯控制器簡(jiǎn)稱PLC））

1、可編程邏輯控制器(programmable logic controller,plc)（可編程邏輯控制器（可編程邏輯控制器，簡(jiǎn)稱PLC）可編程邏輯控制器 (programmable logic controller, plc), 它采用一類可編程的存儲(chǔ)器, 用于其內(nèi)部存儲(chǔ)程序, 執(zhí)行邏輯運(yùn)算、順序控制、定時(shí)、計(jì)數(shù)與算術(shù)操作等面向用戶的指令, 并通過(guò)數(shù)字或模擬式輸入 / 輸出控制各種類型的機(jī)械或生產(chǎn)過(guò)程.可編程邏輯控制器實(shí)質(zhì)是一種專用于工業(yè)控制的計(jì)算機(jī), 其硬件結(jié)構(gòu)基本上與微型計(jì)算機(jī)相同, 基本構(gòu)成為.一、電源可編程邏輯控制器的電源在整個(gè)系統(tǒng)中起著十分重要的作用.如果沒(méi)有一個(gè)良好的、可靠的電源系

2、統(tǒng)是無(wú)法正常工作的, 因此, 可編程邏輯控制器的制造商對(duì)電源的設(shè)計(jì)和制造也十分重視.一般交流電壓波動(dòng)在 + 10% (+ 15%) 范圍內(nèi), 可以不采取其它措施而將plc直接連接到交流電網(wǎng)上去二、中央處理單元 (cpu)中央處理單元 (cpu) 是可編程邏輯控制器的控制中樞.它按照可編程邏輯控制器系統(tǒng)程序賦予的功能接收并存儲(chǔ)從編程器鍵入的用戶程序和數(shù)據(jù); 檢查電源、存儲(chǔ)器、i / o以及警戒定時(shí)器的狀態(tài), 并能診斷用戶程序中的語(yǔ)法錯(cuò)誤.當(dāng)可編程邏輯控制器投入運(yùn)行時(shí), 首先它以掃描的方式接收現(xiàn)場(chǎng)各輸入裝置的狀態(tài)和數(shù)據(jù), 并分別存入i / o映象區(qū), 然后從用戶程序存儲(chǔ)器中逐條讀取用戶程序, 經(jīng)過(guò)

3、命令解釋后按指令的規(guī)定執(zhí)行邏輯或算數(shù)運(yùn)算的結(jié)果送入i / o映象區(qū)或數(shù)據(jù)寄存器內(nèi).等所有的用戶程序執(zhí)行完畢之后, 最后將i / o映象區(qū)的各輸出狀態(tài)或輸出寄存器內(nèi)的數(shù)據(jù)傳送到相 應(yīng)的輸出裝置, 如此循環(huán)運(yùn)行, 直到停止運(yùn)行.為了進(jìn)一步提高可編程邏輯控制器的可靠性, 近年來(lái)對(duì)大型可編程邏輯控制器還采用雙cpu構(gòu)成冗余系統(tǒng), 或采用三cpu的表決式系統(tǒng).這樣, 即使某個(gè)cpu出現(xiàn)故障, 整個(gè)系統(tǒng)仍能正常運(yùn)行.三、存儲(chǔ)器存放系統(tǒng)軟件的存儲(chǔ)器稱為系統(tǒng)程序存儲(chǔ)器.存放應(yīng)用軟件的存儲(chǔ)器稱為用戶程序存儲(chǔ)器.四、輸入輸出接口電路1.現(xiàn)場(chǎng)輸入接口電路由光耦合電路和微機(jī)的輸入接口電路, 作用是可編程邏輯控制器與現(xiàn)

4、場(chǎng)控制的接口界面的輸入通道.2.現(xiàn)場(chǎng)輸出接口電路由輸出數(shù)據(jù)寄存器、選通電路和中斷請(qǐng)求電路集成, 作用可編程邏輯控制器通過(guò)現(xiàn)場(chǎng)輸出接口電路向現(xiàn)場(chǎng)的執(zhí)行部件輸出相應(yīng)的控制信號(hào).五、功能模塊如計(jì)數(shù)、定位等功能模塊.六、通信模塊 1工作原理當(dāng)可編程邏輯控制器投入運(yùn)行后, 其工作過(guò)程一般分為三個(gè)階段, 即輸入采樣、用戶程序執(zhí)行和輸出刷新三個(gè)階段.完成上述三個(gè)階段稱作一個(gè)掃描周期.在整個(gè)運(yùn)行期間, 可編程邏輯控制器的cpu以一定的掃描速度重復(fù)執(zhí)行上述三個(gè)階段.I. input sampling stageIn the input sampling stage, the programmable logic

5、 controller reads all input states and data sequentially in a scanning mode and stores them in the corresponding units in the I/O mapping area. After the input sample is finished, the user is transferred to the user program execution and output refresh stage. In these two stages, the status and data

6、 of the corresponding units in the I/O mapping region will not change even if the input state and data are changed. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scan cycle to ensure that in any case the input can be read in.Two, user program execu

7、tion phaseIn the user program execution phase, the programmable logic controller always scans the user program (ladder diagram) in sequence from top to bottom. In the scanning each ladder, and is always the first scan formed by the contact line control ladder diagram on the left, and left to right a

8、fter, after the first order logic control circuit of a contact form, then according to the result of the logic operation, refresh the logic coil in the system RAM store corresponding bit state; or refresh the output coil in the I/O image area in the corresponding state; or determine whether to execu

9、te the special commands required ladder.That is, in the user program execution process, only the entry point in the I/O region of the image data and the state will not change, and the other output points and soft devices in the I/O image area or RAM system within the storage area and the data are li

10、kely to change, but also ranked in the top of the ladder, the program execution results the row below the ladder diagram is typically used to coil or data play a role; on the contrary, the ladder at the bottom, or the state data can only be refreshed the logic coil to the next scan cycle to act on t

11、he top of the above procedure.In the execution of the program, you can access the I/O point directly if you use the immediate I/O command. That is, if the I/O command is used, the value of the input process image register will not be updated. The program will take the value directly from the I/O mod

12、ule, and the output process image register will be updated immediately, which is somewhat different from the immediate input.Three, output refresh stageWhen the scan user program is finished, the programmable logic controller enters the output refresh phase. During this time, the CPU refreshes all t

13、he output latch circuits in accordance with the corresponding state and data in the I/O mapping area, and then drives the corresponding peripherals through the output circuit. This is the true output of the programmable logic controller.Functional characteristicsProgrammable logic controllers have t

14、he following distinctive features.1. easy to use and easy to programUsing simple ladder diagram, logic diagram or statement table and other programming languages without knowledge of computer, so the system development cycle is short and the field debugging is easy. In addition, you can modify the p

15、rogram online, change the control scheme without removing the hardware.2., strong function, high performance price ratioA small PLC has hundreds of programming components for users to use. It has powerful functions and can achieve very complex control functions. Compared with the relay system with t

16、he same function, it has a high performance price ratio. PLC can realize decentralized control and centralized management through communication networking.3., complete hardware, convenient for users,AdaptablePLC products have been standardization, serialization and modularization, the hardware devic

17、e is equipped with a variety of complete varieties for customers to choose, the user can conveniently conduct system configuration, system composed of different functions and different scale. The installation and wiring of the PLC are also very convenient. The external wiring is usually connected wi

18、th the terminals. PLC has a strong capacity to load, you can directly drive the general solenoid valve and small AC contactor.After the hardware configuration is determined, it can be easily and quickly adapted to the change of process conditions by modifying the user program.4. high reliability and

19、 strong anti-interference abilityThe traditional relay control system uses a large number of intermediate relays and time relays, because of poor contact contact, it is prone to malfunction. PLC software is used instead of a large number of intermediate relay and time relay, leaving only a small amo

20、unt of hardware components and the input and output of the wiring can be reduced to the relay control system of 1/10-1/100, because the contact failure caused by poor greatly reduced.PLC has taken anti interference measures for a series of hardware and software, has a strong anti-interference abilit

21、y, the mean time to failure to reach tens of thousands of hours, can be directly used in the industrial production site with strong interference, PLC the majority of users have been recognized as the most reliable industrial control equipment of A.5., the system design, installation and debugging wo

22、rk is lessPLC replaces the relay relay system with a large number of intermediate relays, time relays, counters and other devices in the relay control system, so that the design, installation and wiring work of the control cabinet are greatly reduced.The ladder diagram program of PLC is usually desi

23、gned by sequential control method. This programming method is very regular and easy to master. For complex control systems, the time required to design a ladder diagram is much less than that of a relay system designed to perform the same function.PLC user program can be simulated in the laboratory

24、debugging, the input signal is simulated with a small switch, through the PLC light-emitting diode can observe the status of the output signal. After completing the installation and wiring of the system, the problems found in the process of debugging in the field can be solved by modifying the progr

25、am, and the debugging time of the system is much less than the relay system.6. maintenance work is small, easy maintenanceThe failure rate of PLC is very low, and it has perfect self diagnosis and display function. Input device and actuator PLC or external fault, can provide PLC based on the light e

26、mitting diode or programmer information quickly identify the cause of the failure, with replacement method module can quickly eliminate itOrigin of historical developmentIn 1968, the General Motors Corporation proposed the replacement of relay control devices;In 1969, the U.S. digital equipment comp

27、any developed the first programmable logic controller PDP 14, successful General Motors Corporation in the production line for the first time trial, by means of the application of electrical control, this is the first generation of programmable logic controller, called Programmable Logic Controller,

28、 referred to as PLC, is recognized as the worlds first PLC.In 1969, the United States developed the worlds first PDP-14;In 1971, Japan developed the first DCS-8;In 1973, the German SIEMENS company (SIEMENS) developed the first European PLC, the model is SIMATIC S4;1974,China developed the first PLC,

29、 and began industrial applications in 1977.DevelopmentMicroprocessors appeared in the early 1970s. People soon introduced it into programmable logic controllers, which enabled the programmable logic controller to increase the functions of operation, data transmission and processing, and completed th

30、e industrial control device with the characteristics of the computer. At this point the programmable logic controller is the product of the combination of microcomputer technology and conventional relay control concepts. After the development of personal computer, in order to facilitate and reflect

31、the functional characteristics of programmable logic controller, the programmable logic controller is named Programmable Logic Controller (PLC).In the middle and late 1970s, programmable logic controller entered the stage of practical development, and computer technology has been fully introduced in

32、to programmable logic controller to make its function leap. Higher computing speed, ultra small volume, more reliable industrial anti-interference design, analog operation, PID function and high cost performance have laid its position in modern industry.Programmable logic controller (PLC) has been w

33、idely used in advanced industrial countries in the early 1980s. Countries in the world that produce programmable controllers are increasing and production is increasing. This indicates that the programmable controller has entered the mature stage.From the middle of 1980s to the middle of 90s, it was

34、 the fastest developing period of programmable logic controller, and the annual growth rate remained 3040%. In this period, PLC capability in dealing with analog and digital computing ability, ability of man-machine interface and network capacity has been greatly improved, the programmable logic con

35、troller gradually into the process control field, in some applications to replace the DCS system at the dominant position in the field of process control.At the end of the twentieth Century, the development of programmable logic controller was more adapted to the needs of modern industry. During thi

36、s period the development of the large machine and super minicomputer, the birth of a variety of special function units, the production of a variety of man-machine interface unit, communication unit, the application of programmable logic controller in the industrial control equipment supporting more

37、easily.system integrationThere is a large amount of sequence control switch open loop mainly in the manufacturing industry, it is in accordance with the logical order of conditions, in accordance with the timing of action action; in addition, the timing has nothing to do with the order according to

38、the logic relation of the chain to protect the control action; and the amount of discrete data acquisition and monitoring of switch quantity, quantity, timing, pulse counter, analog alarming state - based. As a result of these control and surveillance requirements, PLC has evolved into relays, relay

39、s, and sequential control based products. In recent years, PLC manufacturers have gradually added various communication interfaces on the original CPU template, and the field bus technology and Ethernet technology have also been developed synchronously, which makes the application of PLC more and mo

40、re widely. PLC has the advantages of stability, reliability, low price, complete functions, flexible application and convenient operation and maintenance. This is the fundamental reason why it can occupy the market for a long time.The PLC controller hardware itself using modular structure, a motherb

41、oard, digital analog I/O templates, I/O templates, and special positioning template, barcode recognition template module,The user can according to the needs of the extended or equipped with remote I/O to get the number of I/O wants from the station by bus in the motherboard.PLC in the realization of

42、 various number of I/O control at the same time, also has the ability to output analog voltage and digital pulse, so that it can control the servo motor to receive these signals, stepper motor, variable frequency motor, coupled with the touch screen man-machine interface, PLC Schneider can meet you

43、at any level in process control on demand.Selection rulesIn the design of programmable logic controller system, we should first determine the control scheme, and the next step is the programmable logic controller engineering design and selection. The characteristics of the process and application re

44、quirements are the main basis for design selection. The programmable logic controller and related equipment should be integrated, in accordance with the standard, easy and industrial control system as a whole, easy to extend its function of the principle of selection of the programmable logic contro

45、ller is in the industrial field with operation performance, reliable system, system hardware and software configuration and functional programming the logic controller should be compatible with the device size and control requirements. Familiar with the programmable controller, the function diagram

46、and the programming language can shorten the programming time, therefore, the engineering design selection and estimation, control characteristics, detailed analysis of the process requirements, define the task and determine the scope of the operation required and action, then according to the contr

47、ol requirements, estimation, input and output points the required storage capacity, determine the functions of a programmable logic controller, external device characteristics, the final choice of a higher price performance ratio of programmable logic controller and design the corresponding control

48、system.I. estimation of input and output (I/O) pointsThe appropriate margin should be taken into consideration when estimating the I/O number, usually according to the input and output points of statistics, and then increase the expandable margin of 10% to 20%, then the input and output points are u

49、sed to estimate the data. In actual order, the input and output points should be rounded according to the product characteristics of the manufacturers programmable logic controller.Two, memory capacity estimationMemory capacity is the hardware storage unit size of the programmable controller itself

50、can provide the program capacity of user application projects using the storage unit in the memory size, so the process capacity is less than the memory capacity. Design phase, because the user application has not been compiled, therefore, the program capacity is unknown at the design stage and need

51、s to be known only after the program is debugged. In order to estimate the capacity of the program in design selection, memory capacity estimation is usually used instead.There is no fixed formula to estimate the memory, many documents are given in different formulas, generally according to the numb

52、er of I/O points 10 15 times, plus simulation I/O points 100 times, the number of total words of memory (16 bits for a word), also according to the number of 25% consider the allowance.Three, the choice of control functionThe selection includes functions of computation, control, communication, progr

53、amming, diagnosis, and processing speed.1 、 operation functionThe operational functions of a simple programmable logic controller include logic operations, timing and counting functions;General programmable logic controller operation function also includes the function of data shift and comparison o

54、perations; with algebra, data transfer and complex calculation function; large amount of PID computing and other computing functions and advanced simulation programming logic controller. With the emergence of open system, the programmable logic controller has communication function, some products ha

55、ve a communication with the machine, some products have a communication with the parity machine or computer, some products also have the data communication with the factory or enterprise network function. Design selection should proceed from the actual application requirements, and reasonably select

56、 the required operational functions. Most applications need only logic and timing counting function, some applications require data transfer and comparison, when used in analog detection and control, use algebra, numerical conversion and PID operation. Decoding and encoding operations are needed to

57、display data.2, control functionControl functions include PID control operation, feedforward compensation control operation, ratio control operation and so on, and should be determined according to control requirements. Programmable logic controller is mainly used for logic control, therefore, most

58、of the cases used single loop or multi loop controller to solve the analog, sometimes using intelligent input and output unit dedicated to complete the required control function, improve the processing speed of the programmable logic controller and save memory capacity. For example, PID control unit, high-speed counter, analog unit with speed compensation, ASC code conversion unit and so on.3 、 communication functionLarge and medium-sized programmable logic controller systems should support a variety of field buses and standard communications protocols (such as TCP/IP