PLC相關(guān)的外文英語文獻與翻譯(共12頁)

1、精選優(yōu)質(zhì)文檔-傾情為你奉上RelaysThe Programmable Logic ControllerEarly machines were controlled by mechanical means using cams, gears, levers and other basic mechanical devices. As the complexity grew, so did the need for a more sophisticated control system. This system contained wired relay and switch control e

2、lements. These elements were wired as required to provide the control logic necessary for the particular type of machine operation. This was acceptable for a machine that never needed to be changed or modified, but as manufacturing techniques improved and plant changeover to new products became more

3、 desirable and necessary, a more versatile means of controlling this equipment had to be developed. Hardwired relay and switch logic was cumbersome and time consuming to modify. Wiring had to be removed and replaced to provide for the new control scheme required. This modification was difficult and

4、time consuming to design and install and any small "bug" in the design could be a major problem to correct since that also required rewiring of the system. A new means to modify control circuitry was needed. The development and testing ground for this new means was the U.S. auto industry.

5、The time period was the late 1960's and early 1970's and the result was the programmable logic controller, or PLC. Automotive plants were confronted with a change in manufacturing techniques every time a model changed and, in some cases, for changes on the same model if improvements had to b

6、e made during the model year. The PLC provided an easy way to reprogram the wiring rather than actually rewiring the control system.The PLC that was developed during this time was not very easy to program. The language was cumbersome to write and required highly trained programmers. These early devi

7、ces were merely relay replacements and could do very little else. The PLC has at first gradually, and in recent years rapidly developed into a sophisticated and highly versatile control system component. Units today are capable of performing complex math functions including numerical integration and

8、 differentiation and operate at the fast microprocessor speeds now available. Older PLCs were capable of only handling discrete inputs and outputs (that is, on-off type signals), while today's systems can accept and generate analog voltages and currents as well as a wide range of voltage levels

9、and pulsed signals. PLCs are also designed to be rugged. Unlike their personal computer cousin, they can typically withstand vibration, shock, elevated temperatures, and electrical noise to which manufacturing equipment is exposed.As more manufacturers become involved in PLC production and developme

10、nt, and PLC capabilities expand, the programming language is also expanding. This is necessary to allow the programming of these advanced capabilities. Also, manufacturers tend to develop their own versions of ladder logic language (the language used to program PLCs). This complicates learning to pr

11、ogram PLC's in general since one language cannot be learned that is applicable to all types. However, as with other computer languages, once the basics of PLC operation and programming in ladder logic are learned, adapting to the various manufacturers devices is not a complicated process. Most s

12、ystem designers eventually settle on one particular manufacturer that produces a PLC that is personally comfortable to program and has the capabilities suited to his or her area of applications.It should be noted that in usage, a programmable logic controller is generally referred to as a “PLC” or “

13、programmable controller”. Although the term “programmable controller” is generally accepted, it is not abbreviated “PC” because the abbreviation “PC” is usually used in reference to a personal computer. As we will see in this chapter, a PLC is by no means a personal computer.Programmable controllers

14、 (the shortened name used for programmable logic controllers) are much like personal computers in that the user can be overwhelmed by the vast array of options and configurations available. Also, like personal computers, the best teacher of which one to select is experience. As one gains experience

15、with the various options and configurations available, it becomes less confusing to be able to select the unit that will best perform in a particular application. The typical system components for a modularized PLC are:1. Processor.The processor (sometimes call a CPU), as in the self contained units

16、, is generally specified according to memory required for the program to beimplemented. In the modularized versions, capability can also be a factor. This includes features such as higher math functions, PID control loops and optional programming commands. The processor consists of the microprocesso

17、r, system memory, serial communication ports for printer, PLC LAN link and external programming device and, in some cases, the system power supply to power the processor and I/O modules.2. Mounting rack.This is usually a metal framework with a printed circuit board backplane which provides means for

18、 mounting the PLC input/output (I/O) modules and processor. Mounting racks are specified according to the number of modules required to implement the system. The mounting rack provides data and power connections to the processor and modules via the backplane. For CPUs that do not contain a power sup

19、ply, the rack also holds the modular power supply. There are systems in which the processor is mounted separately and connected by cable to the rack. The mounting rack can be available to mount directly to a panel or can be installed in a standard 19" wide equipment cabinet. Mounting racks are

20、cascadable so several may be interconnected to allow a system to accommodate a large number of I/O modules.3. Input and output modules.Input and output (I/O) modules are specified according to the input and output signals associated with the particular application. These modules fall into the catego

21、ries of discrete, analog, high speed counter or register types.Discrete I/O modules are generally capable of handling 8 or 16 and, in some cases 32, on-off type inputs or outputs per module. Modules are specified as input or output but generally not both although some manufacturers now offer modules

22、 that can be configured with both input and output points in the same unit. The module can be specified as AC only, DC only or AC/DC along with the voltage values for which it is designed.Analog input and output modules are available and are specified according to the desired resolution and voltage

23、or current range. As with discrete modules, these are generally input or output; however some manufacturers provide analog input and output in the same module. Analog modules are also available which can directly accept thermocouple inputs for temperature measurement and monitoring by the PLC.Pulsed

24、 inputs to the PLC can be accepted using a high speed countermodule. This module can be capable of measuring the frequency of an inputsignal from a tachometer or other frequency generating device. These modules can also count the incoming pulses if desired. Generally, both frequency and count are av

25、ailable from the same module at the same time if both are required in the application.Register input and output modules transfer 8 or 16 bit words of information to and from the PLC. These words are generally numbers (BCD or Binary) which are generated from thumbwheel switches or encoder systems for

26、 input or data to be output to a display device by the PLC. Other types of modules may be available depending upon the manufacturer of the PLC and it's capabilities. These include specialized communication modules to allow for the transfer of information from one controller to another. One new d

27、evelopment is an I/O Module which allows the serial transfer of information to remote I/O units that can be as far as 12,000 feet away.4. Power supply.The power supply specified depends upon the manufacturer's PLC being utilized in the application. As stated above, in some cases a power supply c

28、apable of delivering all required power for the system is furnished as part of the processor module. If the power supply is a separate module, it must be capable of delivering a current greater than the sum of all the currents needed by the other modules. For systems with the power supply inside the

29、 CPU module, there may be some modules in the system which require excessive power not available from the processor either because of voltage or current requirements that can only be achieved through the addition of a second power source. This is generally true if analog or external communication mo

30、dules are present since these require ± DC supplies which, in the case of analog modules, must be well regulated.5. Programming unit.The programming unit allows the engineer or technician to enter and edit the program to be executed. In it's simplest form it can be a hand held device with a

31、 keypad for program entry and a display device (LED or LCD) for viewing program steps or functions, as shown. More advanced systems employ a separate personal computer which allows the programmer to write, view, edit and download the program to the PLC. This is accomplished with proprietary software

32、 available from the PLC manufacturer. This software also allows the programmer or engineer to monitor the PLC as it is running the program. With this monitoring system, such things as internal coils, registers, timers and other items not visible externally can be monitored to determine proper operat

33、ion. Also, internal register data can be altered if required to fine tune program operation. This can be advantageous when debugging the program. Communication with the programmable controller with this system is via a cable connected to a special programming port on the controller. Connection to th

34、e personal computer can be through a serial port or from a dedicated card installed in the computer.A Programmable Controller is a specialized computer. Since it is a computer, it has all the basic component parts that any other computer has; a Central Processing Unit, Memory, Input Interfacing and

35、Output Interfacing.The Central Processing Unit (CPU) is the control portion of the PLC. It interprets the program commands retrieved from memory and acts on those commands. In present day PLC's this unit is a microprocessor based system. The CPU is housed in the processor module of modularized s

36、ystems.Memory in the system is generally of two types; ROM and RAM. The ROM memory contains the program information that allows the CPU to interpret and act on the Ladder Logic program stored in the RAM memory. RAM memory is generally kept alive with an on-board battery so that ladder programming is

37、 not lost when the system power is removed. This battery can be a standard dry cell or rechargeable nickel-cadmium type. Newer PLC units are now available with Electrically Erasable Programmable Read Only Memory (EEPROM) which does not require a battery. Memory is also housed in the processor module

38、 in modular systems.Input units can be any of several different types depending on input signals expected as described above. The input section can accept discrete or analog signals of various voltage and current levels. Present day controllers offer discrete signal inputs of both AC and DC voltages

39、 from TTL to 250 VDC and from 5 to 250 VAC. Analog input units can accept input levels such as ±10 VDC, ±5 VDC and 4-20 ma. current loop values. Discrete input units present each input to the CPU as a single 1 or 0 while analog input units contain analog to digital conversion circuitry and

40、 present the input voltage to the CPU as binary number normalized to the maximum count available from the unit. The number of bits representing the input voltage or current depends upon the resolution of the unit. This number generally contains a defined number of magnitude bits and a sign bit. Regi

41、ster input units present the word input to the CPU as it is received (Binary or BCD).Output units operate much the same as the input units with the exception that the unit is either sinking (supplying a ground) or sourcing (providing a voltage) discrete voltages or sourcing analog voltage or current

42、. These output signals are presented as directed by the CPU. The output circuit of discrete units can be transistors for TTL and higher DC voltage or Triacs for AC voltage outputs. For higher current applications and situations where a physical contact closure is required, mechanical relay contacts

43、are available. These higher currents, however, are generally limited to about 2-3 amperes. The analog output units have internal circuitry which performs the digital to analog conversion and generates the variable voltage or current output.The first thing the PLC does when it begins to function is u

44、pdate I/O. This means that all discrete input states are recorded from the input unit and all discrete states to be output are transferred to the output unit. Register data generally has specific addresses associated with it for both input and output data referred to as input and output registers. T

45、hese registers are available to the input and output modules requiring them and are updated with the discrete data. Since this is input/output updating, it is referred to as I/O Update. The updating of discrete input and output information is accomplished with the use of input and output image regis

46、ters set aside in the PLC memory. Each discrete input point has associated with it one bit of an input image register. Likewise, each discrete output point has one bit of an output image register associated with it. When I/O updating occurs, each input point that is ON at that time will cause a 1 to

47、 be set at the bit address associated with that particular input. If the input is off, a 0 will be set into the bit address. Memory in today's PLC's is generally configured in 16 bit words. This means that one word of memory can store the states of 16 discrete input points. Therefore, there

48、may be a number of words of memory set aside as the input and output image registers. At I/O update, the status of the input image register is set according to the state of all discrete inputs and the status of the output image register is transferred to the output unit. This transfer of information

49、 typically only occurs at I/O update. It may be forced to occur at other times in PLC's which have an Immediate I/O Update command. This command will force the PLC to update the I/O at other times although this would be a special case.Before a study of PLC programming can begin, it is important

50、to gain a fundamental understanding of the various types of PLCs available, the advantages and disadvantages of each, and the way in which a PLC executes a program. The open frame, shoebox, and modular PLCs are each best suited to specific types of applications based on the environmental conditions,

51、 number of inputs and outputs, ease of expansion, and method of entering and monitoring the program. Additionally, programming requires a prior knowledge of the manner in which a PLC receives input information, executes a program, and sends output information. With this information, we are now prepa

52、red to begin a study of PLC programming techniques.When writing programs for PLCs, it is beneficial to have a background in ladder diagramming for machine controls. This is basically the material that was covered in Chapter 1 of this text. The reason for this is that at a fundamental level, ladder l

53、ogic programs for PLCs are very similar to electrical ladder diagrams. This is no coincidence.The engineers that developed the PLC programming language were sensitive to the fact that most engineers, technicians and electricians who work with electrical machines on a day-to-day basis will be familia

54、r with this method of representing control logic. This would allow someone new to PLCs, but familiar with control diagrams, to be able to adapt very quickly to the programming language. It is likely that PLC programming language is one of the easiest programming languages to learn.可編程序控制器早期的機器用機械的方法

55、采用凸輪控制、齒輪、杠桿和其他基本機械設(shè)備。增長的復雜性,因此需要一種更了復雜的控制系統(tǒng)。該系統(tǒng)包含有線繼電器和開關(guān)控制元素。這些元素,要求提供有線控制邏輯的必要特定類型的機器上運行。這是一臺機器,不接受需要變更或修改,但作為制造技術(shù)改進和植物轉(zhuǎn)換為新產(chǎn)品變得更加理想的和必要的,一個更加多才多藝該設(shè)備具有控制手段,發(fā)展。繼電器和開關(guān)特性的邏輯是笨重,費時要修改。線路必須拆卸和更換提供新的控制方案的要求。這個修改是針對設(shè)計、安裝、消費的設(shè)需要正確接線系統(tǒng)。一個新的方式修改控制電路是需要的。開發(fā)和測試基地為這個新的方法美國的汽車工業(yè)。晚的時間是1960年代至1970年代初,結(jié)果是采用可編程序控制器

56、PLC。面對汽車需要改變生產(chǎn)工藝改變每一次模型,在某些情況下,改善同一模型是在做了模型的一年。PLC提供一個簡單的方法來重組接線,而不是實際電路重組的控制系統(tǒng)。開發(fā)了PLC,在這段時間里是不太容易計劃的。這PLC語言是難于書寫和需要受過高度訓練的程序員。這些早期的僅僅是傳遞裝置,可以隨心所欲的做很少就可以完成預先的任務。PLC在近年來迅速發(fā)展成為一種具有非常高的通用性控制系統(tǒng)的組成部分。今天已經(jīng)能夠執(zhí)行復雜的運算功能包括數(shù)值積分的分化與已開放操作快速處理器的速度。曾經(jīng)的PLC可只處理離散輸入輸出(即開關(guān)式信號),而今天的系統(tǒng)能夠接受并產(chǎn)生模擬的電壓和電流以及廣泛的電壓水平和脈沖信號。PLC設(shè)計

57、的目的也是非常明確的。不像個人電腦,它們可以典型地操作振動、沖擊、高溫、電子噪聲、生產(chǎn)設(shè)備暴露等。隨著越來越多的廠商卷入了可編程序控制器(PLC)的生產(chǎn)和開發(fā),以及可編程序控制器(PLC)能力的拓展,編程語言也就隨之增強了。需要這些先進的編程能力是有必要的。同時,制造商往往發(fā)展自己版本的使用于語言程序(PLC)的梯形邏輯語言。這個復雜可編程邏輯控制器(PLC)在學習編程的時候,既然一個可適用于所有的類型語言不能完全做到了解。然而,就像其他的計算機語言一樣,可編程序控制器(PLC)的基本操作和編程邏輯是有學習階段，去適應不同廠家的設(shè)備，這不是一個復雜的過程。大多數(shù)的系統(tǒng)設(shè)計師最終在一個特定的制造

58、廠商自己產(chǎn)生一個可編程序控制器(PLC)的程序并具備適合它的地區(qū)性的應用能力。應該指出的是,使用一個可編程邏輯控制器,普遍被稱為“PLC”或“可編程控制器”。雖然術(shù)語“可編程控制器”已被普遍接受,但它并不是縮寫“PC”，因為簡稱的“PC”通常用于個人電腦。正如我們所看到的, PLC控制絕不是一臺個人電腦?？删幊炭刂破?縮短名字用于可編程邏輯控制器)像個人電腦用戶可以做出了巨量的選擇和配置。來到使用者面前,就像個人電腦，是最好老師的一個很好的選擇?？紤]到不同的收益和配置的選擇,它就可以選擇單位，使其變得能夠?qū)⒆詈玫芈男性谝粋€特定的應用。典型的系統(tǒng)部件模塊化可編程序控制器(PLC)是:1、處理器處

59、理器(有時叫一個CPU),就像在獨立控制單元,通常是根據(jù)指定的內(nèi)存需求為程序是什么實施。在模塊化的版本,能力也可以是一個重要的因素。這包括高等數(shù)學功能等特點,采用PID控制回路可編程的命令。處理器構(gòu)成的微處理器、系統(tǒng)內(nèi)存,串行通訊港口打印機,可編程序控制器(PLC)局域網(wǎng)連接裝置和外部編程,在某些情況下,該系統(tǒng)供電電源處理器和I / O模塊。2、安裝架這通常是金屬框架,印刷電路板提供用于安裝底板意味著PLC輸入/輸出(I / O)模塊和處理器。指定安裝架是根據(jù)模塊的數(shù)量必須執(zhí)行系統(tǒng)。安裝架提供數(shù)據(jù)和電力連接處理器與模塊通過底板。對于cpu,它不包含一個電源、架子上也成立這種模塊化的電力供應。有系統(tǒng)處理器安裝連接電纜單獨架子上。安裝架能可直接向山面板或者可以安裝在標準19“寬設(shè)備內(nèi)閣。cascadable安裝架是這么多允許一個系統(tǒng)互連來容納大量I / O模塊。3。輸入和輸出模塊輸入和輸出(I / O)模塊根據(jù)輸入指定輸出信號與之關(guān)聯(lián)的特定應用程序。這些模塊秋天分成離散、模擬、高速計數(shù)器或注冊類型。離散I / O模塊一般都是有能力處理8和16,在某些情況下,開關(guān)類型的輸入和輸出一個模塊。模塊指定為輸入或輸出,但一般雖然一些制造商們提供了模塊可配置和輸入輸出點在同一單元內(nèi)。模擬輸入和輸出模塊都是可行的