外文翻譯--可編程邏輯控制器

1、<p>　　Programmable logic controller</p><p>　　A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of

2、 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 designed for multiple inputs and output arrangement

3、s, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control m</p><p>　　1. History</p><p>　　The PLC was invented in response to the n

4、eeds of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when pr

5、oduction models changed.</p><p>　　Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum se

6、quencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as electricians needed to individually rewire each and ever

7、y relay.</p><p>　　In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems. The winning proposal

8、came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a new company dedicated t

9、o developing, manufacturing, selling, and servicing this new product: Modicon, which stood for </p><p>　　One of the very first 084 models built is now on display at Modicon's headquarters in North Andove

10、r, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appear

11、ance.</p><p>　　The automotive industry is still one of the largest users of PLCs.</p><p>　　2. Development</p><p>　　Early PLCs were designed to replace relay logic systems. These PLC

12、s were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used

13、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, from ladder logic to more traditional programming languages such as B

14、ASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams.</p><p>　　Many early PLCs did not have accompanying programming t

15、erminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming

16、 terminals evolved, it became more common for ladder logic to be used, for the aforementioned reasons. Newer formats such as State Logic and Function Block (which is similar to the way logic is depicted when using digita

17、l int</p><p>　　2.1 Programming</p><p>　　Early PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated

18、function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. The v

19、ery oldest PLCs used non-volatile magnetic core memory.</p><p>　　More recently, PLCs are programmed using application software on personal computers. The computer is connected to the PLC through Ethernet, RS

20、-232, RS-485 or RS-422 cabling. The programming software allows entry and editing of the ladder-style logic. Generally the software provides functions for debugging and troubleshooting the PLC software, for example, by h

21、ighlighting portions of the logic to show current status during operation or via simulation. The software will upload and download the PLC</p><p>　　3. Functionality</p><p>　　The functionality of

22、 the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabil

23、ities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.

24、Regarding the practicality of these desk</p><p>　　In more recent years, small products called PLRs (programmable logic relays), and also by similar names, have become more common and accepted. These are very

25、 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 involved, and low cost is desired. These small devices are typical

26、ly 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 Topics</p><p>　　4.1 Features</p><p>　　The

27、 main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sens

28、ors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate elec

29、tric motors, pneumatic or hydraulic cylinders, magnetic r</p><p>　　4.2 System scale</p><p>　　A small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expan

30、sions 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 modules with different functions. The processor and selection of I/

31、O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special high speed serial I/O link is used so that racks ca

32、n be distributed away from the processor, reducing the wiring costs for large plants.</p><p>　　4.3 User interface</p><p>　　PLCs may need to interact with people for the purpose of configuration,

33、 alarm reporting or everyday control.</p><p>　　A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a

34、 programming and monitoring software installed on a computer, with the PLC connected via a communication interface.</p><p>　　4.4 Communications</p><p>　　PLCs have built in communications ports,

35、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 include various fieldbuses such as DeviceNet or Profibus. Other co

36、mmunications protocols that may be used are listed in the List of automation protocols.</p><p>　　Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supe

37、rvisory Control and Data Acquisition) system or web browser.</p><p>　　PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex pro

38、cess to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI devices such as keypads or PC-type workstations.</p>

39、<p>　　4.5 Programming</p><p>　　PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The program

40、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 relays.</p><p>　　Under the IEC 61131-3 standard, PL

41、Cs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. Initially most PLCs utilized Ladder L

42、ogic Diagram Programming, a model which emulated electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced. This model remains common today.</p><p>　　IEC 61131-3 c

43、urrently defines five programming languages for programmable control systems: FBD (Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the Pascal programming language), IL (Instruction list, sim

44、ilar to assembly language) and SFC (Sequential function chart). These techniques emphasize logical organization of operations.</p><p>　　While the fundamental concepts of PLC programming are common to all man

45、ufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manuf

46、acturer, different models may not be directly compatible.</p><p>　　5. PLC compared with other control systems</p><p>　　PLCs are well-adapted to a range of automation tasks. These are typically i

47、ndustrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its o

48、perational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired </p><

49、;p>　　For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in product

50、ion quantities.</p><p>　　A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies, input/output hardware

51、 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 are an example; millions of units are built each year, and very

52、 few end-users alter the programming of these controllers. However, some specialty vehicles such a</p><p>　　Very complex process control, such as used in the chemical industry, may require algorithms and per

53、formance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls.</p><p>　　Programmable control

54、lers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so that G-code (involving a CNC machine) can be used to instruct m

55、achine movements.</p><p>　　PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller". A PID loop could be used to

56、 control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed con

57、trol system (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC application</p><p>　　PLCs have similar functionality as Remote Terminal Units. An RTU, however, us

58、ually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper, RTUs, PLCs and DCSs are increasingly beginning to overlap in responsibilities, and many vendors sell RTUs

59、 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 PLCs, although nearly all vendors also offer pr</p><p

60、>　　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, True or False, respectively). Push buttons, limit switches, an

61、d photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as on and another as off. For example, a PLC mi

62、ght 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 like volume controls, with a range of values between zero an

63、d 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 bits available to store the data. As PLCs typically use 16-bi

64、t signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage o</p><p&g

65、t;<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電過程自動化的數(shù)字計算機，例如控制機械廠生產(chǎn)線、游樂設(shè)施或照明裝置?？删幊炭刂破髟谠S多工業(yè)和機器中使用。與通用的計算機不同的是，PLC是專為多個輸入和輸出管理，擴展溫度范圍、不受電磁噪音影響、抗震動和沖擊所設(shè)計?？刂破鞯牟僮鞒绦蛲ǔ４鎯υ陔姵毓╇娀蚍且资缘膬?nèi)存中。PLC是實時的系

66、統(tǒng)，因為系統(tǒng)產(chǎn)生的輸出結(jié)果必須在有限的時間內(nèi)回饋到輸入，否則會導致錯誤操作。</p><p><b>　　1.歷史</b></p><p>　　PLC發(fā)明是針對于美國汽車制造行業(yè)的需要。可編程邏輯控制器最初通過了在軟件版本更換硬連線的控制板生產(chǎn)模式更改時的汽車工業(yè)。</p><p>　　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

67、或上千的繼電器、凸輪計時器、鼓定序儀和專用的閉環(huán)控制器來完成的。在每年更新模型等設(shè)施轉(zhuǎn)變過程是非常耗時并且成本高昂的，這是因為電工需要單獨地再接電線給每個中轉(zhuǎn)。</p><p>　　在1968年 GM Hydramatic（自動輸電分局）發(fā)布通用汽車公司的提議，電子替代布線中繼系統(tǒng)。獲獎的提案來自貝得福得，馬薩諸塞的貝得福得同事。第一個PLC選定084，因為它是貝得福得同事的第八十四個項目。貝得福得同事建立了一家

68、新的公司致力開發(fā)、生產(chǎn)、銷售，和服務這一新產(chǎn)品：Modicon，代表模塊化數(shù)字控制器。迪克·莫利，被認為是PLC之父，他是從事該項目的人之一。1977年古爾德電子公司當前所有者收購法國施耐德電氣公司同德國公司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。這是專門為通用汽車服務的，并且經(jīng)過了近二十多年的不間斷服務。直至984出現(xiàn)

69、，Modicon使用的84名字才在其產(chǎn)品范圍中結(jié)束。</p><p>　　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)計來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現(xiàn)有技術(shù)人員的培訓需求。其他

70、早期的可編程控制器使用指令列表編程，基于一個堆棧編程邏輯求解器進行求解。</p><p>　　現(xiàn)代可編程控制器在各種各樣的方式可以被編程，從梯形邏輯語言到更加傳統(tǒng)的編程語言例如BASIC和C語言。另一個方法是狀態(tài)邏輯，被設(shè)計的一種非常高級編程語言根據(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有可編程終端的邏輯圖形表示法，邏輯反而是被描繪成一系列在一些版本的布

71、爾格式的邏輯表達式，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的梯形邏輯語言。更新的格式如國家邏輯和功能塊（這是類似的邏輯描述使用數(shù)字邏輯集成電路時的方式）的存在，但它們?nèi)詻]有梯形邏輯語言流行。一個主要原因是可編程控制器解決問題用一個可預測和重復的序列的邏輯，并且梯形邏輯語言可以用其他格式讓程序員（寫邏輯）的人看到邏輯的時間，所有問題更加容易地程序化。</p><p><b>　　2.1編

72、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。</p><p>　　最期PLC在個人計算機上使用應用軟件編程。計算機連接到PLC通過以太網(wǎng)RS-232,RS-485或RS-4

73、22纜線連接。編程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，例如在操作過程中或通過仿真的邏輯部分PLC軟件突出顯示當前狀態(tài)。該軟件將上傳和下載PLC程序以便備份和恢復。在某些型號的PLC中雖然程序?qū)懭胍粋€可移動的芯片，如EEPROM或EPROM，但該方案還是得從個人電腦傳輸?shù)絇LC編程版。</p><p><b>　　3.功能</b></p><

74、p>　　PLC的功能經(jīng)過多年的發(fā)展，包括連續(xù)的繼電器控制，運動控制，過程控制，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，處理能力和通信能力相當于臺式電腦。PLC編程結(jié)合遠程I/O硬件，一臺通用臺式計算機允許在某些應用中重疊使用某一可編程控制器。在重工業(yè)中PLC被認為沒有這些桌面計算機為主的邏輯控制器的實際性強，因為PLC在臺式計算機系統(tǒng)中運行不是很穩(wěn)定，并且，因為臺式計算機硬件沒有被設(shè)計成耐溫度、濕氣、振動和耐用作為可

75、編程控制器的處理器。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邏輯不可能總是對規(guī)定邏輯變化的輸入狀態(tài)與極端性預計的時間一致。盡管如此，這樣桌面邏輯被應用在較不重要情況，像實驗室自動化和小型設(shè)施中使用該應用程序的要求不高，因為他們的價格一般都遠遠低于昂貴的PLC。</p><p>　　在最近數(shù)年，小產(chǎn)品稱為PLR（可編程邏輯繼電器），并且因為名字相似，變得更常

76、見并被接受。這些很像PLC已經(jīng)應用于輕工業(yè)，它只有少部分的輸入/輸出（例如一些真實的輸入輸出信號）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2個模擬輸入。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)備有一個小郵票大小的液晶屏幕來觀看簡化梯子邏輯的輸

77、入/輸出點（只有一小部分程序被可見于給定的時間）和狀況，并且這些屏幕由一個電磁四通搖臂按鈕操縱加上四個不同的用于瀏覽和編輯的邏輯電鈕，類似于錄像機遙控按鈕。控制器大多數(shù)有一個小插座為通過連接RS-232或RS-485到個人計算機，以便程序員可能為編程使用簡單的窗口應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，大大擴展,控制器通常不會取模塊化并且不是可擴展的，但是他們提供穩(wěn)健設(shè)計的確定性和執(zhí)行邏輯的價值比PLC少。&

78、lt;/p><p>　　4.可編程序控制器PLC</p><p><b>　　4.1未來發(fā)展</b></p><p>　　從其他計算機來看，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。可編程控制器是讀取限制開關(guān)、模擬過程變量（如溫度和壓力）以及位置復雜的定

79、位系統(tǒng)。有些人利用機器系統(tǒng)來查看光源與照明。執(zhí)行器使可編程控制器操作電子電機、氣動或液壓缸、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簡單的可編程控制器、或可編程序控制器可以用外部的I/O模塊連接插入的計算機網(wǎng)絡(luò)。</p><p><b>　　4.2系統(tǒng)規(guī)模</b></p><p>　　一個小的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

80、夠的I/O通常可擴展。</p><p>　　模塊化可編程控制器有一個機箱（也稱為機架）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用程序。幾個機架可以有一個單個的處理器，可能會有成千上萬的輸入和輸出。一種特殊的高速串行I/O環(huán)節(jié)是機架減少多個線路使用分布式離散處理器。</p><p><b>　　4.3使用界面</b></p>

81、<p>　　可編程控制器的配置、報警報告或日常控件可能需要與人進行交互。</p><p>　　一個簡單的系統(tǒng)可能使用按鈕和指示燈與用戶進行交互?？梢杂脠D形觸摸屏文本顯示。更復雜的系統(tǒng)使用PLC通過通信接口連接到一臺計算機上安裝的編程和監(jiān)測軟件來使用。</p><p><b>　　4.4通信</b></p><p>　　可編程控制器被建

82、于通常的9針RS-232，也可以選擇485或以太網(wǎng)的通信端口由環(huán)境影響評估。協(xié)議、BACnet或東方是通常作為通信協(xié)議之一包含其中。其它選項包括各項如構(gòu)架或現(xiàn)場總線。在自動化協(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一個網(wǎng)絡(luò)，以一些其它的系統(tǒng)（例如，運行監(jiān)控、監(jiān)測控制與數(shù)據(jù)采集 系統(tǒng)）或網(wǎng)絡(luò)瀏覽器的計算機進行通信。</p><p>　　可編

83、程控制器在較大的I/O系統(tǒng)中使用可能會有處理器之間的對等，這允許獨立的部分是一個復雜的過程,同時讓獨立的控制子系統(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程序通常是個人的計算機上寫入一個特殊的應用程序，然后通過連接電纜或以上PLC網(wǎng)絡(luò)直接下載。該程序存儲在

84、PLC備用電池內(nèi)存或一些其他非易失性閃存中。通常，一個單一的PLC可以進行編程，以替換數(shù)以千計的繼電器。</p><p>　　根據(jù)IEC61131-3的標準可以使用基于標準的編程語言編程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的。</p><p>　　IEC61

85、131-3當前定義的可編程控制系統(tǒng)的五個編程語言：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言）、IL（教學列表，類似于匯編語言）和SFC（順序功能圖）。這些技術(shù)強調(diào)邏輯組織的行動。</p><p>　　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程序意味著不會不完全的可互換。即使在同一個單一的制造商產(chǎn)品線內(nèi)不同的模型可能不直接兼容。<

86、;/p><p>　　5.PLC相比其它控制系統(tǒng)</p><p>　　可編程控制器是可適應一系列自動化任務。這些都是自動化的在制造中通常工業(yè)過程開發(fā)和維護自動化系統(tǒng)的成本在哪里高，相對于總成本和其壽命期間預計將對系統(tǒng)更改?？删幊炭刂破靼斎牒洼敵鲈O(shè)備兼容工業(yè)試驗設(shè)備和管制，小電氣的設(shè)計問題對預期操作是必要的。PLC應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）的費用比一個具體

87、定制設(shè)計的小控制器要高。另外一方面在批量生產(chǎn)貨物的情況下自定義的控制系統(tǒng)是組成、成本較低的最佳選擇，而不是一個非反復出現(xiàn)工程費用“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單的固定自動化任務。例如消費者用的洗碗機的機電凸輪計時器生產(chǎn)數(shù)量成本只有幾美元。</p><p>　　一種基于微控制器的設(shè)計是需要成百上千個單位（設(shè)計電源供應器，輸入/輸出硬件和必要的檢測和認

88、證）和開發(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。汽車應用程序就是一個例子：數(shù)以百萬計的內(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)計的控制,而不是用PLC，因為數(shù)量很低,發(fā)展成本會賺不到錢的。</p><p>　　像使用在化工中的過程控件就非常復雜，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

89、決方案，例如飛機飛行的控件。</p><p>　　可編程序控制器廣泛用于運動控制、定位控制和轉(zhuǎn)矩控制。一些制造商生產(chǎn)運動控制單元與PLC集成、G-code（涉及數(shù)控機床）可以用于指導機器運作。</p><p>　　可編程控制器可能包括一個“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

90、制器將使用分布式的控制系統(tǒng)（DCS）的過程成百上千的循環(huán)?？删幊炭刂破鞴δ芤呀?jīng)很強大了，可編程序控制器（PLC）與集散控制系統(tǒng)之間的邊界應用已經(jīng)不是很明顯了。</p><p>　　可編程控制器具有類似于遠程終端設(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大和更便宜，RTU、PLC和DCS正在越來越多地開始有重疊，職責，并與PLC賣許多供應商的特點類似，RTU反之亦然。業(yè)界基于IEC

91、61131-3創(chuàng)建程序上運行的RTU和PLC功能塊語言規(guī)范，盡管幾乎所有供應商還提供專有的替代方案及相關(guān)的開發(fā)環(huán)境。</p><p><b>　　6.數(shù)字和模擬信號</b></p><p>　　數(shù)字或離散信號就像二進制開關(guān)，創(chuàng)造出一個簡單的開或關(guān)信號（分別為1或0，真或假）。按鈕、限制的交換機和光電傳感器都是提供一個離散的信號的設(shè)備。離散信號發(fā)送使用電壓或電流，在特定

92、的范圍，對指定，另一個為關(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。</p><p>　　模擬信號就像音量控制范圍從0開始。這些通常被解釋為整數(shù)值（計數(shù)），PLC與各種范圍的精度取決于設(shè)備和用于存儲數(shù)據(jù)的位數(shù)。可編程控制器通常使用16位二進制符號的處理器，范圍-32768和32767之間的整數(shù)值。通常由模擬信號表