外文翻譯---可編程邏輯控制器 (2)

1、<p><b>　　外文文獻(xiàn)翻譯</b></p><p>　　Programmable logic controller[11]</p><p>　　A programmable logic controller (PLC) or programmable controller is a digital computer used for automatio

2、n of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is

3、 designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control m</p><p><b>　　1.History<

4、/b></p><p>　　The PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry where softwar

5、e revision replaced the re-wiring of hard-wired control panels when production models changed.</p><p>　　Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accom

6、plished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and

7、expensive, as electricians needed to individually rewire each and every relay.</p><p>　　In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an elec

8、tronic replacement for hard-wired relay systems. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project

9、, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for </p><p>　　One of the very first 084 models

10、 built is now on display at Modicon's headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84

11、 moniker at the end of its product range until the 984 made its appearance.</p><p>　　The automotive industry is still one of the largest users of PLCs.</p><p>　　2.Development</p><p>

12、;　　Early PLCs were designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce

13、training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver.</p><p>　　Modern PLCs can be programmed in a variety of ways,

14、from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams.</p>

15、;<p>　　Many early PLCs did not have accompanying programming terminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some

16、version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, for the aforementioned reasons. Newer formats such as State Logic and Function B

17、lock (which is similar to the way logic is depicted when using digital int</p><p>　　2.1Programming</p><p>　　Early PLCs, up to the mid-1980s, were programmed using proprietary programming panels

18、or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and d

19、ocumentation were very minimal due to lack of memory capacity. The very oldest PLCs used non-volatile magnetic core memory.</p><p>　　More recently, PLCs are programmed using application software on personal

20、computers. The computer is connected to the PLC through Ethernet, RS-232, RS-485 or RS-422 cabling. The programming software allows entry and editing of the ladder-style logic. Generally the software provides functions f

21、or debugging and troubleshooting the PLC software, for example, by highlighting portions of the logic to show current status during operation or via simulation. The software will upload and download the PLC</p>&l

22、t;p>　　3.Functionality</p><p>　　The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The

23、 data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purp

24、ose desktop computer to overlap some PLCs in certain applications. Regarding the practicality of these desk</p><p>　　In more recent years, small products called PLRs (programmable logic relays), and also by

25、similar names, have become more common and accepted. These are very much like PLCs, and are used in light industry where only a few points of I/O (i.e. a few signals coming in from the real world and a few going out) are

26、 involved, and low cost is desired. These small devices are typically made in a common physical size and shape by several manufacturers, and branded by the makers of larger PLCs to fill out </p><p>　　4.PLC T

27、opics</p><p>　　4.1.Features</p><p>　　The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extens

28、ive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems

29、. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic r</p><p>　　4.2System scale</p><p>　　A small PLC will have a fixed number

30、 of connections built in for inputs and outputs. Typically, expansions are available if the base model has insufficient I/O.</p><p>　　Modular PLCs have a chassis (also called a rack) into which are placed mo

31、dules with different functions. The processor and selection of I/O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outpu

32、ts. A special high speed serial I/O link is used so that racks can be distributed away from the processor, reducing the wiring costs for large plants.</p><p>　　4.3User interface</p><p>　　PLCs ma

33、y need to interact with people for the purpose of configuration, alarm reporting or everyday control.</p><p>　　A simple system may use buttons and lights to interact with the user. Text displays are availabl

34、e as well as graphical touch screens. More complex systems use a programming and monitoring software installed on a computer, with the PLC connected via a communication interface.</p><p>　　4.4Communications&

35、lt;/p><p>　　PLCs have built in communications ports, usually 9-pin RS-232, but optionally EIA-485 or Ethernet. Modbus, BACnet or DF1 is usually included as one of the communications protocols. Other options inc

36、lude various fieldbuses such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols.</p><p>　　Most modern PLCs can communicate over a network

37、 to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser.</p><p>　　PLCs used in larger I/O systems may have peer-to-peer (P2P) communication

38、between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for H

39、MI devices such as keypads or PC-type workstations.</p><p>　　4.5Programming</p><p>　　PLC programs are typically written in a special application on a personal computer, then downloaded by a dire

40、ct-connection cable or over a network to the PLC. The program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory. Often, a single PLC can be programmed to replace thousands of re

41、lays.</p><p>　　Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain p

42、rogrammable controllers. Initially most PLCs utilized Ladder Logic Diagram Programming, a model which emulated electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced. This m

43、odel remains common today.</p><p>　　IEC 61131-3 currently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar

44、to the Pascal programming language), IL (Instruction list, similar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations.</p><p>　　While the

45、 fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between differe

46、nt makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.</p><p>　　5.PLC compared with other control systems</p><p>　　PLCs are well-

47、adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, a

48、nd where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the des

49、ign problem centers on expressing the desired </p><p>　　For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an elec

50、tromechanical cam timer costing only a few dollars in production quantities.</p><p>　　A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the deve

51、lopment cost (design of power supplies, input/output hardware and necessary testing and certification) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications ar

52、e an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such a</p><p>　　Very complex process control, such as

53、used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraf

54、t flight controls.</p><p>　　Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so th

55、at G-code (involving a CNC machine) can be used to instruct machine movements.</p><p>　　PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative&quo

56、t; or "PID controller". A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where process

57、es required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC application</p><p>　　PLCs have simila

58、r functionality as Remote Terminal Units. An RTU, however, usually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper, RTUs, PLCs and DCSs are increasingly beginni

59、ng to overlap in responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The industry has standardized on the IEC 61131-3 functional block language for creating programs to run on RTUs and PLC

60、s, although nearly all vendors also offer pr</p><p>　　6.Digital and analog signals</p><p>　　Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, Tr

61、ue or False, respectively). Push buttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range i

62、s designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate v</p><p>　　Analog signals are

63、like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of b

64、its available to store the data. As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog

65、signals. Analog signals can use voltage o</p><p><b>　　可編程邏輯控制器</b></p><p>　　可編程邏輯控制器（PLC）或可編程序控制器是用于機(jī)電過(guò)程自動(dòng)化的數(shù)字計(jì)算機(jī)，例如控制機(jī)械廠生產(chǎn)線、游樂(lè)設(shè)施或照明裝置?？删幊炭刂破髟谠S多工業(yè)和機(jī)器中使用。與通用的計(jì)算機(jī)不同的是，PLC是專為多個(gè)輸入和輸出管理，擴(kuò)

66、展溫度范圍、不受電磁噪音影響、抗震動(dòng)和沖擊所設(shè)計(jì)。控制器的操作程序通常存儲(chǔ)在電池供電或非易失性的內(nèi)存中。PLC是實(shí)時(shí)的系統(tǒng)，因?yàn)橄到y(tǒng)產(chǎn)生的輸出結(jié)果必須在有限的時(shí)間內(nèi)回饋到輸入，否則會(huì)導(dǎo)致錯(cuò)誤操作。</p><p><b>　　1.歷史</b></p><p>　　PLC發(fā)明是針對(duì)于美國(guó)汽車制造行業(yè)的需要?？删幊踢壿嬁刂破髯畛跬ㄟ^(guò)了在軟件版本更換硬連線的控制板生產(chǎn)模式更

67、改時(shí)的汽車工業(yè)。在PLC之前，控制、程序化和安全聯(lián)鎖邏輯制造汽車是使用上百或上千的繼電器、凸輪計(jì)時(shí)器、鼓定序儀和專用的閉環(huán)控制器來(lái)完成的。在每年更新模型等設(shè)施轉(zhuǎn)變過(guò)程是非常耗時(shí)并且成本高昂的，這是因?yàn)殡姽ば枰獑为?dú)地再接電線給每個(gè)中轉(zhuǎn)。</p><p>　　在1968年 GM Hydramatic（自動(dòng)輸電分局）發(fā)布通用汽車公司的提議，電子替代布線中繼系統(tǒng)。獲獎(jiǎng)的提案來(lái)自貝得福得，馬薩諸塞的貝得福得同事。第一個(gè)PL

68、C選定084，因?yàn)樗秦惖酶５猛碌牡诎耸膫€(gè)項(xiàng)目。貝得福得同事建立了一家新的公司致力開(kāi)發(fā)、生產(chǎn)、銷售，和服務(wù)這一新產(chǎn)品：Modicon，代表模塊化數(shù)字控制器。迪克·莫利，被認(rèn)為是PLC之父，他是從事該項(xiàng)目的人之一。1977年古爾德電子公司當(dāng)前所有者收購(gòu)法國(guó)施耐德電氣公司同德國(guó)公司AEG并售予該品牌為Modicon。</p><p>　　084模型之一首次被設(shè)在北部安多弗的Modicon總部馬薩諸塞州。

69、這是專門為通用汽車服務(wù)的，并且經(jīng)過(guò)了近二十多年的不間斷服務(wù)。直至984出現(xiàn)，Modicon使用的84名字才在其產(chǎn)品范圍中結(jié)束。汽車工業(yè)仍是PLC的最大用戶之一。</p><p><b>　　2.發(fā)展</b></p><p>　　早期的可編程控制器是設(shè)計(jì)來(lái)取代繼電器邏輯系統(tǒng)。這些可編程控制器的“階梯邏輯”是與繼電器邏輯示意圖非常類似的。選擇此程序表示法的目的是為了減少對(duì)

70、現(xiàn)有技術(shù)人員的培訓(xùn)需求。其他早期的可編程控制器使用指令列表編程，基于一個(gè)堆棧編程邏輯求解器進(jìn)行求解。</p><p>　　現(xiàn)代可編程控制器在各種各樣的方式可以被編程，從梯形邏輯語(yǔ)言到更加傳統(tǒng)的編程語(yǔ)言例如BASIC和C語(yǔ)言。另一個(gè)方法是狀態(tài)邏輯，被設(shè)計(jì)的一種非常高級(jí)編程語(yǔ)言根據(jù)狀態(tài)轉(zhuǎn)換圖的可編程控制器編程。</p><p>　　很多早期可編程控制器沒(méi)有可編程終端的邏輯圖形表示法，邏輯反而是

71、被描繪成一系列在一些版本的布爾格式的邏輯表達(dá)式，類似于布爾代數(shù)。隨著編程碼發(fā)展，由于上述原因它變成更常見(jiàn)的梯形邏輯語(yǔ)言。更新的格式如國(guó)家邏輯和功能塊（這是類似的邏輯描述使用數(shù)字邏輯集成電路時(shí)的方式）的存在，但它們?nèi)詻](méi)有梯形邏輯語(yǔ)言流行。一個(gè)主要原因是可編程控制器解決問(wèn)題用一個(gè)可預(yù)測(cè)和重復(fù)的序列的邏輯，并且梯形邏輯語(yǔ)言可以用其他格式讓程序員（寫邏輯）的人看到邏輯的時(shí)間，所有問(wèn)題更加容易地程序化。</p><p>&

72、lt;b>　　2.1編程</b></p><p>　　早期的PLC，到80年代中期，都是用專有的編程版或?qū)Ｓ镁幊探K端，往往有專門的功能鍵，代表各種PLC程序邏輯元件。程序存儲(chǔ)在盒式磁帶盒上。由于缺少的內(nèi)存容量很少用于打印設(shè)備。最古老的可編程控制器使用的是非易失性磁核心內(nèi)存。最期PLC在個(gè)人計(jì)算機(jī)上使用應(yīng)用軟件編程。計(jì)算機(jī)連接到PLC通過(guò)以太網(wǎng)RS-232,RS-485或RS-422纜線連接。編程

73、軟件允許輸入梯式邏輯編程。通常，軟件提供了用于調(diào)試和故障排除的功能，例如在操作過(guò)程中或通過(guò)仿真的邏輯部分PLC軟件突出顯示當(dāng)前狀態(tài)。該軟件將上傳和下載PLC程序以便備份和恢復(fù)。在某些型號(hào)的PLC中雖然程序?qū)懭胍粋€(gè)可移動(dòng)的芯片，如EEPROM或EPROM，但該方案還是得從個(gè)人電腦傳輸?shù)絇LC編程版。</p><p><b>　　3.功能</b></p><p>　　PL

74、C的功能經(jīng)過(guò)多年的發(fā)展，包括連續(xù)的繼電器控制，運(yùn)動(dòng)控制，過(guò)程控制，分布式控制系統(tǒng)和網(wǎng)絡(luò)。一些現(xiàn)代PLC的數(shù)據(jù)處理，存儲(chǔ)，處理能力和通信能力相當(dāng)于臺(tái)式電腦。PLC編程結(jié)合遠(yuǎn)程I/O硬件，一臺(tái)通用臺(tái)式計(jì)算機(jī)允許在某些應(yīng)用中重疊使用某一可編程控制器。在重工業(yè)中PLC被認(rèn)為沒(méi)有這些桌面計(jì)算機(jī)為主的邏輯控制器的實(shí)際性強(qiáng)，因?yàn)镻LC在臺(tái)式計(jì)算機(jī)系統(tǒng)中運(yùn)行不是很穩(wěn)定，并且，因?yàn)榕_(tái)式計(jì)算機(jī)硬件沒(méi)有被設(shè)計(jì)成耐溫度、濕氣、振動(dòng)和耐用作為可編程控制器的處理器

75、。除桌面基于邏輯的硬件局限之外，例如Windows操作系統(tǒng)不適合自己的確定性邏輯的執(zhí)行，結(jié)果是PLC邏輯不可能總是對(duì)規(guī)定邏輯變化的輸入狀態(tài)與極端性預(yù)計(jì)的時(shí)間一致。盡管如此，這樣桌面邏輯被應(yīng)用在較不重要情況，像實(shí)驗(yàn)室自動(dòng)化和小型設(shè)施中使用該應(yīng)用程序的要求不高，因?yàn)樗麄兊膬r(jià)格一般都遠(yuǎn)遠(yuǎn)低于昂貴的PLC。</p><p>　　在最近數(shù)年，小產(chǎn)品稱為PLR（可編程邏輯繼電器），并且因?yàn)槊窒嗨?，變得更常?jiàn)并被接受。這些很

76、像PLC已經(jīng)應(yīng)用于輕工業(yè)，它只有少部分的輸入/輸出（例如一些真實(shí)的輸入輸出信號(hào)）參與，低成本，很理想。這些小設(shè)備尺寸和形狀比較普通地幾位制造商制作，并且由更大的PLC制作商來(lái)填滿他們低端產(chǎn)品規(guī)格。俗名包括PICO控制器、納米PLC和其他的小控制器。多數(shù)這些控制器有在8到12數(shù)字輸入、4到8數(shù)字輸出，多達(dá)2個(gè)模擬輸入。尺寸通常是4英寸寬、3英寸高、3英寸深。大多數(shù)這樣的設(shè)備有一個(gè)小郵票大小的液晶屏幕來(lái)觀看簡(jiǎn)化梯子邏輯的輸入/輸出點(diǎn)（只有一

77、小部分程序被可見(jiàn)于給定的時(shí)間）和狀況，并且這些屏幕由一個(gè)電磁四通搖臂按鈕操縱加上四個(gè)不同的用于瀏覽和編輯的邏輯電鈕，類似于錄像機(jī)遙控按鈕?？刂破鞔蠖鄶?shù)有一個(gè)小插座為通過(guò)連接RS-232或RS-485到個(gè)人計(jì)算機(jī)，以便程序員可能為編程使用簡(jiǎn)單的窗口應(yīng)用而不是被迫使用微小的LCD和電鈕。不像普通PLC，通常是模塊化，大大擴(kuò)展,控制器通常不會(huì)取模塊化并且不是可擴(kuò)展的，但是他們提供穩(wěn)健設(shè)計(jì)的確定性和執(zhí)行邏輯的價(jià)值比PLC少。</p>

78、<p>　　4.可編程序控制器PLC</p><p><b>　　4.1未來(lái)發(fā)展</b></p><p>　　從其他計(jì)算機(jī)來(lái)看，主要區(qū)別是可編程控制器具有特殊條件（例如，灰塵、濕、熱、冷）和具有廣泛的輸入/輸出（I/O）安排的設(shè)施。這些是連接PLC的傳感器和執(zhí)行器?？删幊炭刂破魇亲x取限制開(kāi)關(guān)、模擬過(guò)程變量（如溫度和壓力）以及位置復(fù)雜的定位系統(tǒng)。有些人利用

79、機(jī)器系統(tǒng)來(lái)查看光源與照明。執(zhí)行器使可編程控制器操作電子電機(jī)、氣動(dòng)或液壓缸、磁繼電器、電磁線圈的模擬輸出。輸入/輸出的安排可以建立一個(gè)簡(jiǎn)單的可編程控制器、或可編程序控制器可以用外部的I/O模塊連接插入的計(jì)算機(jī)網(wǎng)絡(luò)。</p><p><b>　　4.2系統(tǒng)規(guī)模</b></p><p>　　一個(gè)小的PLC是固定數(shù)量的輸入和輸出生成的連接。如果基礎(chǔ)模型具有足夠的I/O通?？蓴U(kuò)

80、展。</p><p>　　模塊化可編程控制器有一個(gè)機(jī)箱（也稱為機(jī)架）在其中放置具有不同的功能模塊。處理器和I/O模塊的選擇被定制為特定的應(yīng)用程序。幾個(gè)機(jī)架可以有一個(gè)單個(gè)的處理器，可能會(huì)有成千上萬(wàn)的輸入和輸出。一種特殊的高速串行I/O環(huán)節(jié)是機(jī)架減少多個(gè)線路使用分布式離散處理器。</p><p><b>　　4.3使用界面</b></p><p>

81、　　可編程控制器的配置、報(bào)警報(bào)告或日?？丶赡苄枰c人進(jìn)行交互。</p><p>　　一個(gè)簡(jiǎn)單的系統(tǒng)可能使用按鈕和指示燈與用戶進(jìn)行交互?？梢杂脠D形觸摸屏文本顯示。更復(fù)雜的系統(tǒng)使用PLC通過(guò)通信接口連接到一臺(tái)計(jì)算機(jī)上安裝的編程和監(jiān)測(cè)軟件來(lái)使用。</p><p><b>　　4.4通信</b></p><p>　　可編程控制器被建于通常的9針RS-

82、232，也可以選擇485或以太網(wǎng)的通信端口由環(huán)境影響評(píng)估。協(xié)議、BACnet或東方是通常作為通信協(xié)議之一包含其中。其它選項(xiàng)包括各項(xiàng)如構(gòu)架或現(xiàn)場(chǎng)總線。在自動(dòng)化協(xié)議的列表中列出了其他可能使用的通信協(xié)議。</p><p>　　最現(xiàn)代的可編程控制器可以通過(guò)一個(gè)網(wǎng)絡(luò)，以一些其它的系統(tǒng)（例如，運(yùn)行監(jiān)控、監(jiān)測(cè)控制與數(shù)據(jù)采集 系統(tǒng)）或網(wǎng)絡(luò)瀏覽器的計(jì)算機(jī)進(jìn)行通信。</p><p>　　可編程控制器在較大的I

83、/O系統(tǒng)中使用可能會(huì)有處理器之間的對(duì)等，這允許獨(dú)立的部分是一個(gè)復(fù)雜的過(guò)程,同時(shí)讓獨(dú)立的控制子系統(tǒng)的溝通聯(lián)系協(xié)調(diào)。這些通信鏈接也經(jīng)常用于人機(jī)界面設(shè)備（例如鍵盤或PC型工作站）。</p><p><b>　　4.5編程</b></p><p>　　PLC程序通常是個(gè)人的計(jì)算機(jī)上寫入一個(gè)特殊的應(yīng)用程序，然后通過(guò)連接電纜或以上PLC網(wǎng)絡(luò)直接下載。該程序存儲(chǔ)在PLC備用電池內(nèi)存

84、或一些其他非易失性閃存中。通常，一個(gè)單一的PLC可以進(jìn)行編程，以替換數(shù)以千計(jì)的繼電器。</p><p>　　根據(jù)IEC61131-3的標(biāo)準(zhǔn)可以使用基于標(biāo)準(zhǔn)的編程語(yǔ)言編程PLC?？稍谀承┛删幊炭刂破魃险{(diào)用順序功能圖圖形編程表示法。最初大多數(shù)可編程控制器利用階梯邏輯圖的模式，模擬機(jī)電控制面板設(shè)備（如繼電器與線圈的聯(lián)系）。此模型今天仍然是常見(jiàn)的。</p><p>　　IEC61131-3當(dāng)前定義

85、的可編程控制系統(tǒng)的五個(gè)編程語(yǔ)言：FBD（功能塊圖）LD（梯形圖）、ST（結(jié)構(gòu)化文本，類似于帕斯卡爾的編程語(yǔ)言）、IL（教學(xué)列表，類似于匯編語(yǔ)言）和SFC（順序功能圖）。這些技術(shù)強(qiáng)調(diào)邏輯組織的行動(dòng)。雖然PLC編程的基本概念是共同所有的生產(chǎn)商，I/O處理、內(nèi)存組織和指令集不同設(shè)置PLC程序意味著不會(huì)不完全的可互換。即使在同一個(gè)單一的制造商產(chǎn)品線內(nèi)不同的模型可能不直接兼容。</p><p>　　5.PLC相比其它控制系

86、統(tǒng)</p><p>　　可編程控制器是可適應(yīng)一系列自動(dòng)化任務(wù)。這些都是自動(dòng)化的在制造中通常工業(yè)過(guò)程開(kāi)發(fā)和維護(hù)自動(dòng)化系統(tǒng)的成本在哪里高，相對(duì)于總成本和其壽命期間預(yù)計(jì)將對(duì)系統(tǒng)更改?？删幊炭刂破靼斎牒洼敵鲈O(shè)備兼容工業(yè)試驗(yàn)設(shè)備和管制，小電氣的設(shè)計(jì)問(wèn)題對(duì)預(yù)期操作是必要的。PLC應(yīng)用程序通常是高度定制系統(tǒng)，因此成本包裝可編程序控制器（PLC）的費(fèi)用比一個(gè)具體定制設(shè)計(jì)的小控制器要高。另外一方面在批量生產(chǎn)貨物的情況下自定義的

87、控制系統(tǒng)是組成、成本較低的最佳選擇，而不是一個(gè)非反復(fù)出現(xiàn)工程費(fèi)用“普通”的解決方案。</p><p>　　不同的技術(shù)方法有大量的并且很簡(jiǎn)單的固定自動(dòng)化任務(wù)。例如消費(fèi)者用的洗碗機(jī)的機(jī)電凸輪計(jì)時(shí)器生產(chǎn)數(shù)量成本只有幾美元。</p><p>　　一種基于微控制器的設(shè)計(jì)是需要成百上千個(gè)單位（設(shè)計(jì)電源供應(yīng)器，輸入/輸出硬件和必要的檢測(cè)和認(rèn)證）和開(kāi)發(fā)成本可以分散到很多的銷售，最終用戶不需要更改該控件。汽

88、車應(yīng)用程序就是一個(gè)例子：數(shù)以百萬(wàn)計(jì)的內(nèi)置單位每一年需要建造，很少最終用戶更改這些控制器的編程。然而，一些其他車輛如交通公共汽車經(jīng)常定制設(shè)計(jì)的控制,而不是用PLC，因?yàn)閿?shù)量很低,發(fā)展成本會(huì)賺不到錢的。</p><p>　　像使用在化工中的過(guò)程控件就非常復(fù)雜，可能需要算法和甚至超出高性能可編程控制器。非常高速的能力范圍的性能或精度控件也可能需要自定義的解決方案，例如飛機(jī)飛行的控件?？删幊绦蚩刂破鲝V泛用于運(yùn)動(dòng)控制、定位

89、控制和轉(zhuǎn)矩控制。一些制造商生產(chǎn)運(yùn)動(dòng)控制單元與PLC集成、G-code（涉及數(shù)控機(jī)床）可以用于指導(dǎo)機(jī)器運(yùn)作。</p><p>　　可編程控制器可能包括一個(gè)“比例，積分，微分”的單變量反饋模擬控制循環(huán)的邏輯或“控制器”。以PID回路可用于控制溫度為例。歷史上PLC通常配置只有少數(shù)模擬控制回路，通常配置可編程控制器將使用分布式的控制系統(tǒng)（DCS）的過(guò)程成百上千的循環(huán)?？删幊炭刂破鞴δ芤呀?jīng)很強(qiáng)大了，可編程序控制器（PLC

90、）與集散控制系統(tǒng)之間的邊界應(yīng)用已經(jīng)不是很明顯了。</p><p>　　可編程控制器具有類似于遠(yuǎn)程終端設(shè)備的功能。RTU，然而通常不支持或控制回路的控制算法。隨著硬件迅速變得更強(qiáng)大和更便宜，RTU、PLC和DCS正在越來(lái)越多地開(kāi)始有重疊，職責(zé)，并與PLC賣許多供應(yīng)商的特點(diǎn)類似，RTU反之亦然。業(yè)界基于IEC61131-3創(chuàng)建程序上運(yùn)行的RTU和PLC功能塊語(yǔ)言規(guī)范，盡管幾乎所有供應(yīng)商還提供專有的替代方案及相關(guān)的開(kāi)發(fā)

91、環(huán)境。</p><p><b>　　6.數(shù)字和模擬信號(hào)</b></p><p>　　數(shù)字或離散信號(hào)就像二進(jìn)制開(kāi)關(guān)，創(chuàng)造出一個(gè)簡(jiǎn)單的開(kāi)或關(guān)信號(hào)（分別為1或0，真或假）。按鈕、限制的交換機(jī)和光電傳感器都是提供一個(gè)離散的信號(hào)的設(shè)備。離散信號(hào)發(fā)送使用電壓或電流，在特定的范圍，對(duì)指定，另一個(gè)為關(guān)閉。例如PLC可能24V直流I/O，使用值為以上22DC 代表上，2VDC下面的值表

92、示關(guān)閉，和中間值未定義。最初，可編程控制器只有離散的I/O。模擬信號(hào)就像音量控制范圍從0開(kāi)始。這些通常被解釋為整數(shù)值（計(jì)數(shù)），PLC與各種范圍的精度取決于設(shè)備和用于存儲(chǔ)數(shù)據(jù)的位數(shù)?？删幊炭刂破魍ǔＪ褂?6位二進(jìn)制符號(hào)的處理器，范圍-32768和32767之間的整數(shù)值。通常由模擬信號(hào)表示壓力、溫度、流量和重量。模擬信號(hào)可以使用大小成比例電壓或電流過(guò)程信號(hào)的值。例如一個(gè)模擬0-10V或4-20mA的輸入將轉(zhuǎn)換為一個(gè)整數(shù)值0-32767。&l