可編程序控制器外文翻譯2

1、<p><b>　　外文原文</b></p><p>　　Programmable Logic Controllers versus Personal Computers for Process Control</p><p>　　Industrial Engineering Department</p><p>　　Universi

2、ty of Puerto Rico</p><p>　　P.O. Box 5000</p><p>　　Mayaguez, Puerto Rico 00681</p><p><b>　　ABSTRACT</b></p><p>　　It is proposed that Personal Computers (PCs)

3、 can be used effectively for the same industrial applications as Programmable Logic Controllers (PLCs). The basic concepts related to the operation of a PLC to emulate the behavior of a relay panel are explained. This is

4、 used to build a simple model for using standard PCs in the same applications as PLCs. This is demonstrated using a simple example of an automated process, Sample code in a standard high level language is presented that

5、can be used as a</p><p>　　Keywords: Programmable Logic Controller, Personal Computer, Automation, Ladder Logic, Relay Panels</p><p>　　INTRODUCTION</p><p>　　Personal Computers (PCs)

6、can be used effectively for the same applications as Programmable Logic Controllers (PLCs). A modem PLC is a computer-based device designed to control a process. It relates information coming from sensors that monitor th

7、e state of a process, with the status of some actuators that are capable of changing it. This relationship is established in most cases in Boolean logic. Typical sensors used in industrial applications include limit swit

8、ches, proximity sensors, and other </p><p>　　Fig. 1: Model of Simple Process</p><p>　　RELAY PANELS</p><p>　　PLCs wore designed to replace relay panels. These are custom made control

9、lers dedicated to a particular application. They can be expensive for complex systems, cannot be easily reconfigured, are difficult to troubleshoot, consume lots of energy, have a relatively moderate speed of operation,

10、 and have low reliability. Relay panels are not the most suitable alternative for a moderate to complex industrial application where flexibility, ease of maintenance and troubleshooting are very important. O</p>&

11、lt;p>　　The electrical control circuits of relay panels are generally drawn using so-called electric ladder diagrams. They differ slightly from conventional wiring diagrams in that they do not show the physical arrange

12、ment of the components, but emphasize the function of each circuit. They are a set of parallel circuits that in essence represent a hardwired program that controls the sequence of operations in a given process. Being ele

13、ctrical circuits in parallel gives the advantage of solving all the co</p><p>　　Fig. 2: Electric Ladder Diagram</p><p>　　PLCs are typically computer-based, solid-state, single-processor devices

14、that emulate the behavior of an electric ladder diagram. Since they are sequential machines, to emulate the workings of parallel circuits that respond instantaneously, PLCs use an input/output image table and a scanning

15、cycle.</p><p>　　An input/output image table is a memory structure that stores all the relevant information about the current scanning cycle. It can be subdivided in three basic parts: the input table, the o

16、utput table, and the internal relay table, The current state of the inputs (sensors) is kept in the input table; the desired state of the outputs (actuators) is kept in the output table; and the state of the virtual cont

17、rol relays is kept in the internal relay table.</p><p>　　When a program is being nm in a PLC it is continuously executing a scanning cycle (fig. 3). The scanning cycle has two major parts (in an actual PLC i

18、t has other parts but two are relevant here for the sake of the discussion): the input/output scan, and the program scan. In the input/output scan the current state of the inputs is read from the input points and stored

19、in the input table, and the desired state of the</p><p>　　Fig. 3: PLC Scanning Cycle</p><p>　　outputs (from the output table) is sent to the output points. The program scan solves the Boolean lo

20、gic that relates the information in the input table, with that in the output and internal relay tables. Also, the information in the output and internal relay tables is updated during the program scan. In a PLC this Bool

21、ean logic is typically represented in a graphical language that looks very much like the electrical circuit that it emulates. This language is known as ladder logic. In fig. 4 ther</p><p>　　Fig, 4: PLC Ladde

22、r Logic</p><p>　　PLCs overcome all of the relay panel shortcomings and currently are the most widely used industrial automation controllers. At the time of their introduction they were very successful becaus

23、e their language, ladder logic, was based tm electric ladder diagrams which engineers and electricians of the time were already familiar with. Nevertheless, PLCs have some shortcomings of their own that are evident when

24、compared with other available technology. Some of the most limiting ones include: them is</p><p>　　PERSONAL COMPUTERS</p><p>　　Another technology that could be used for the same purpose is the

25、standard personal computer (PC). The PC is becoming increasingly popular for process control. A PC-based controller model is proposed here which could replace PLCs in any industrial control application and would open up

26、a world of possibilities in software development, standard components, and connectivity in general. This medal includes an industry-standard PC running any modem operating system, a set of standard input/output mod</p

27、><p>　　A SIMPLE EXAMPLE</p><p>　　The proposed model will be presented through a sample program coded in Turbo Pascal~ for the control of the process shown in fig. 1. Assume that sensors are connect

28、ed to the PC through input port hex address 3BD, and that actuators are connected to output port hen address 3BC, as shown in figs. 5 and 6 respectively.</p><p>　　Fig. 5: Input Connections</p><p&g

29、t;　　Fig. 6: Output Connections</p><p>　　The sample Pascal program is shown in fig. 7. The image tables: input, output, and internal relays, are implemented using Pascal Boolean variables. When any of these

30、variables is TRUE, that represents an ON state; and whoa they are FALSE that represents an OFF state. When exchanging signals with the input and output points an ON state is represented by a logical "0" and an

31、OFF state with a logical "1".</p><p>　　The main program is an emulation of the PLC scanning cycle presented in fig. 3. In this simplified example it is assumed that the PLC will be running its prog

32、ram until a key is pressed on the PC keyboard. Other device can be used if it is desired to use the PC keyboard for other more productive purpose.</p><p>　　The input/output scan is emulated using subroutine

33、I_ O_Scan. There, the 8 bit input port (fig. 5) is read and the status of the individual bits stored in the input table. Also the status of the output points from the output table is written to the 8 bit output port (se

34、e fig. 6). The Program _Scan subroutine is a direct translation of the ladder diagram in fig. 4. For every rung in the ladder logic there is an if-then-else statement. The Initialize and Finalize subroutines worn added t

35、o handle </p><p><b>　　. </b></p><p>　　Fig.7:Sample Pascal Program</p><p>　　It should be noted that this is a very simplified example whose purpose is to provide a framew

36、ork for control program development on a PC combining the programming paradigms of standard procedural high-level languages with the familiar PLC ladder logic. Although it cannot be fully demonstrated in this paper, it p

37、rovides a simple way of simultaneous control of parallel processes without considering the intricacies of a particular operating system. It demonstrates that complex custom software does</p><p>　　The propose

38、d model would be very easy to adapt and implement even in-house because it can still use ladder logic, so no new technological skills are necessary. Any typical PLC instructions can be added to the model very easily, inc

39、luding timers, counters, one-shots, and so on. Other custom PLC instructions suited to a particular application can be included that use the features of high level languages, making it more powerful than standard PLC lad

40、der logic.</p><p>　　ADVANTAGES OF PERSONAL COMPUTERS</p><p>　　The PC is a standard hardware/software platform. PCs improve at a rapid pace, become cheaper, and have mom power than PLCs. Pentium

41、systems widely available today outperform even the fastest margins of 20:1 or more. A new generation of PCs becomes available every six to nine months. By contrast new generation of PLC hardware becomes available every t

42、wo to three years. PCs with at least 16Mbytes are commonplace, while PLCs still have memory in the order of Kbytes. The PC supports more standard pe</p><p>　　It has been envisioned that the next generation i

43、ndustrial controls should provide an open architecture and a single software development environment. The trend will be to move away from closed, proprietary systems due to the advantages an open architecture provides. I

44、t gives more flexibility since users do have to "marry" to a particular supplier. There is easier access to the latest technology since numerous independent developers are continuously advancing the functionali

45、ty and ease of use of</p><p>　　The PC can provide a totally integrated solution that incorporates the functions of the PLC, the man-machine interface, and the programming terminal. It can provide process sim

46、ulation/emulation so that complete software development can be done independent of the hardware. Also, it can provide sophisticated troubleshooting and diagnostic tools, providing in-depth analysis of the state of the m

47、achine, possible causes for malfunction, and recommended remedies. You can even run off-the-shelf Window</p><p>　　PCs for industrial control might be successful today for reasons analogous to those for the P

48、LCs at the time of their introduction; engineers today are well versed in computer programming and technology. Many sites already have significant PC programming expertise on hand. Also, the typical PC language paradigms

49、 lend themselves more readily to flowcharting techniques and languages of recent development for control programming, such as Sequential Function Charts.</p><p>　　DISADVANTAGES OF PERSONAL COMPUTERS</p>

50、;<p>　　Commercial-grade PCs are not normally designed to tolerate the shock, vibration, temperature, and electrical noise frequently found on the manufacturing floor~:1. Even though hardware that meets these envir

51、onmental conditions is readily available as both PLCs and PCs, this may increase the cost of implementing PC-based control. PCs may not be cost effective for applications with few I/O points (90% of the market). Very che

52、ap PLCs are available for that market. PCs are visualized as solutions for</p><p><b>　　中文翻譯</b></p><p>　　可編程序控制器與個(gè)人計(jì)算機(jī)在過程控制中的對(duì)比</p><p><b>　　工業(yè)工程部門</b></p&

53、gt;<p><b>　　波多里哥大學(xué)</b></p><p>　　P .O . 信箱5000</p><p>　　Mayaguez, 波多里哥00681</p><p><b>　　摘要</b></p><p>　　有人提議,個(gè)人計(jì)算機(jī)(PCs) 和可編程序的邏輯控制器(PLCs )

54、一樣，能有效地使用在工業(yè)應(yīng)用上。與PLC 的使用有關(guān)的基本概念可由繼電控制板的動(dòng)作來解釋。這使基于標(biāo)準(zhǔn)個(gè)人計(jì)算機(jī)建立一個(gè)簡單的模型，能和基于PLC的一樣。本文列舉了一個(gè)使用自動(dòng)化過程的簡單的例子,樣品代碼會(huì)由一種標(biāo)準(zhǔn)高級(jí)語言提出，這種高級(jí)語言可能被用作為模板。最后,提出了使用個(gè)人計(jì)算機(jī)做過程控制的潛在的好處和一些改進(jìn)措施。</p><p>　　主題詞: 可編程序控制器, 個(gè)人計(jì)算機(jī), 自動(dòng)化, 梯形圖, 繼電控制

55、板</p><p><b>　　介紹</b></p><p>　　個(gè)人計(jì)算機(jī)(個(gè)人計(jì)算機(jī)) 和可編程序的邏輯控制器(PLCs) 一樣，可能有效地被用應(yīng)用 ?，F(xiàn)代PLC 控制過程，是以計(jì)算機(jī)為基礎(chǔ)的。它的關(guān)系信息來自監(jiān)測過程狀態(tài)的傳感器,是能改變它一些傳動(dòng)裝置的狀態(tài)。這個(gè)關(guān)系被建立在布爾邏輯的情況下。典型的工業(yè)中應(yīng)用的傳感器包括限位開關(guān),鄰近傳感器,及二進(jìn)制傳感器。傳動(dòng)

56、裝置可能包括螺線管,馬達(dá)起始者,和一些其它相關(guān)的設(shè)備。圖1顯示了一種工業(yè)應(yīng)用的一個(gè)簡化的模型，該模型中 PLC 得到應(yīng)用。</p><p>　　圖1 簡化的過程模型</p><p>　　PLC替換繼電控制板。這些定制的控制器致力于一種特殊應(yīng)用。因?yàn)閺?fù)雜系統(tǒng),它們的造價(jià)高，很難重新構(gòu)造,出現(xiàn)故障也不容易發(fā)現(xiàn),消耗許多能量,適當(dāng)?shù)牟僮魉俣?和低可靠性。在要求維護(hù)靈活、方便，而且又要快速查明故障

57、的復(fù)雜工業(yè)應(yīng)用中，繼電控制板不是最適當(dāng)?shù)倪x擇。另一方面,他們相對(duì)地易學(xué)，容易被電工和非工程學(xué)人員了解。繼電控制板電子控制電路一般使用梯形圖。它們與常規(guī)接線圖小小的不同是他們不顯示組分的物理安排,但強(qiáng)調(diào)各條電路的作用。他們實(shí)質(zhì)上代表一個(gè)被硬聯(lián)線的節(jié)目控制操作，序列在一個(gè)指定的過程中的一套并聯(lián)電路。電子電路的平行設(shè)計(jì)為解決所有控制邏輯帶來好處，可以同時(shí)和瞬間動(dòng)作。圖2 代表一張?zhí)菪螆D，可以控制如圖1 所示的工業(yè)過程。</p>

58、<p><b>　　圖2 梯形圖</b></p><p>　　PLC是典型地計(jì)算機(jī)為主的,不用真空管的,與梯形圖的動(dòng)作一致的唯一處理器設(shè)備。因?yàn)樗麄兪沁B續(xù)機(jī)器,實(shí)時(shí)地反應(yīng)并聯(lián)電路的工作,PLC使用輸入/輸出 表和掃描周期。</p><p>　　輸入/輸出表是一種記憶結(jié)構(gòu)，它存儲(chǔ)關(guān)于當(dāng)前的掃描周期的所有的相關(guān)的信息。它被細(xì)分為三種基本的部分:輸入表,輸出表,和

59、內(nèi)部繼電表,輸入(傳感器的)狀態(tài)被保留在輸入表;輸出(傳動(dòng)裝置)期待狀態(tài)被保留在輸出表;真正控制繼電器的狀態(tài)被保留在內(nèi)部繼電表中。</p><p>　　圖3 PLC掃描周期</p><p>　　當(dāng)程序是在PLC中運(yùn)行，它連續(xù)的執(zhí)行掃描周期(圖 3)。掃描周期有二大部分(在實(shí)際PLC中，它有其它部分，這里只討論相關(guān)的):輸入掃描和程序掃描。在輸入程序掃描輸入的狀態(tài)，從輸入點(diǎn)和被存放的輸入表中

60、讀入,并且程序的期待狀態(tài)(從輸出表)送到輸出點(diǎn)。程序掃描解決布爾邏輯，它關(guān)系到在輸入表的信息,在輸出和內(nèi)部繼電表的信息。而且,信息在輸出和內(nèi)部繼電表在程序掃描期間更新。在PLC 中這種布爾邏輯典型地代表圖形語言，這種圖形語言看起來像它仿真的電子電路。人所皆知，這種語言為梯形邏輯語言。圖4的梯形邏輯程序可能使用在圖1的控制過程中。注意，在圖 2中相似的電子梯形圖。PLC 掃描周期的好處是,在繼電控制板中，它允許廣泛的過程一致地被控制。&l

61、t;/p><p>　　圖4 PLC梯形邏輯</p><p>　　PLC能克服所有繼電控制板缺點(diǎn)，目前是被廣泛應(yīng)用的工業(yè)自動(dòng)化控制器。因?yàn)樗鼈兊恼Z言，在它們的介紹之時(shí)它們是非常成功的，梯形邏輯,是電子工程師和梯形圖編程人員已經(jīng)通曉的電子梯形圖。然而,顯然PLC與其它可利用的技術(shù)比較，也有它們自己的一些缺點(diǎn)。它的局限有:它們是沒有工業(yè)標(biāo)準(zhǔn)的硬件或軟件平臺(tái),它們會(huì)限制程序員 做的控制活動(dòng)和操作,并且

62、為了降低成本，它的計(jì)算能力相對(duì)低。</p><p><b>　　個(gè)人計(jì)算機(jī)</b></p><p>　　標(biāo)準(zhǔn)個(gè)人計(jì)算機(jī)(個(gè)人計(jì)算機(jī)) ，一種為達(dá)到同樣目的的其它技術(shù)。它變得越來越普遍。在任一種工業(yè)控制應(yīng)用中,一個(gè)基于個(gè)人計(jì)算機(jī)的控制器模型能替換PLC?？赡軙?huì)在軟件開發(fā)領(lǐng)域會(huì)開辟一個(gè)世界，因?yàn)樗臉?biāo)準(zhǔn)組分和連通性。這個(gè)模型包括一臺(tái)能運(yùn)行在任一個(gè)現(xiàn)代開放操作系統(tǒng)的標(biāo)準(zhǔn)個(gè)人

63、計(jì)算機(jī), 一套等效于典型的PLC中的輸入模塊的標(biāo)準(zhǔn)輸入產(chǎn)品模塊, 還有用于實(shí)施一個(gè)PLC 掃描周期的任一種高級(jí)編程語言。</p><p><b>　　一個(gè)簡單的例子</b></p><p>　　提出的模型將通過一個(gè)抽樣程序被編碼在Turbo Pascal ，作為過程的控制，如圖1所示. 假設(shè), 傳感器通過輸入端十六進(jìn)制地址3BD被連接到個(gè)人計(jì)算機(jī), 并且, 傳動(dòng)裝置被

64、連接到輸出端口十六進(jìn)制地址3BC,地址分配如圖 5 、圖6所示。</p><p><b>　　圖5 輸入連接</b></p><p><b>　　圖6 輸出連接</b></p><p>　　樣品Pascal程序如圖 7所示。圖像表:輸入,輸出,和繼電表,使用Pascal布爾變量。當(dāng)這些變量是真的,那代表開狀態(tài);而當(dāng)他們是假

65、的,代表關(guān)狀態(tài)。當(dāng)交換信號(hào)以輸入和輸出指向開狀態(tài)代表一邏輯"0" 而關(guān)狀態(tài)代表一邏輯"1" 。</p><p><b>　　圖7 程序示例</b></p><p>　　注意,這是一個(gè)非常簡化的例子，目的是為熟悉的PLC梯形邏輯的控制程序提供框架，以使個(gè)人計(jì)算機(jī)結(jié)合標(biāo)準(zhǔn)程序高級(jí)語言編程。雖然在本文里，沒有做充分的說明,但是它提供平

66、行的過程，沒有考慮一個(gè)特殊操作系統(tǒng)的復(fù)雜，而且控制一個(gè)簡單的方式。這說明,復(fù)雜的自定義軟件不一定要做這項(xiàng)技術(shù)工作。</p><p>　　提出的模型非常容易適應(yīng)和實(shí)施，因?yàn)樗匀皇褂锰菪芜壿?那么就不一定要新技術(shù)。所有典型的PLC 指示可以非常容易地增加到模型,包括定時(shí)器,計(jì)數(shù)器 等等。其它的適合于特殊應(yīng)用的PLC可能包括使用高級(jí)語言，這又使它比標(biāo)準(zhǔn)PLC 梯形邏輯強(qiáng)有力。</p><p>

67、<b>　　個(gè)人計(jì)算機(jī)的優(yōu)點(diǎn)</b></p><p>　　個(gè)人計(jì)算機(jī)是標(biāo)準(zhǔn)硬件軟件平臺(tái)。個(gè)人計(jì)算機(jī)以快速步伐改善,變得更加便宜,并且比PLC有更多力量。在奔騰系統(tǒng)廣泛利用的今天，個(gè)人計(jì)算機(jī)勝過最快速的PLC 近20:1甚至更多。每六個(gè)到九個(gè)月，個(gè)人計(jì)算機(jī)就更新?lián)Q代。相反每二到三年P(guān)LC 硬件更新一次。至少的在個(gè)人計(jì)算機(jī)中，16Mbytes是普遍的, 同時(shí)PLC仍然的記憶區(qū)是按Kbyte 的順

68、序。個(gè)人計(jì)算機(jī)支持更加標(biāo)準(zhǔn)的外圍設(shè)備，譬如大容量只讀存儲(chǔ)器驅(qū)動(dòng)器,聲卡,鼠標(biāo),網(wǎng)絡(luò)設(shè)施,等等，可從許多販賣者以合適的價(jià)格買到。通過許多販賣者，個(gè)人計(jì)算機(jī)是在短時(shí)間內(nèi)在全世界廣泛使用。</p><p>　　有人構(gòu)想,下一代工業(yè)控制應(yīng)該提供一個(gè)開放式體系結(jié)構(gòu)和一個(gè)唯一軟件開發(fā)環(huán)境。 趨向?qū)⑹亲叱龇忾],專有系統(tǒng)依賴一個(gè)開放式體系結(jié)構(gòu)提供的好處。用戶必須和一個(gè)特殊供應(yīng)商"結(jié)婚" ，這提供了更多的靈活性

69、。，因?yàn)樵S多獨(dú)立開發(fā)商連續(xù)推進(jìn)個(gè)人計(jì)算機(jī)，這些計(jì)算機(jī)兼容硬件和軟件的功能，且易用，這使得對(duì)新的技術(shù)的掌握變的更加的容易,因?yàn)橛?jì)算機(jī)的巨大的市場，它提供一個(gè)競爭環(huán)境，而且經(jīng)濟(jì)的原因驅(qū)使廠商們將價(jià)格壓到最低，因此成本效率高。</p><p>　　個(gè)人計(jì)算機(jī)可能提供合并PLC的一種完全解決方案,基于人機(jī)接口和編程的終端。它能提供過程模仿，使得不依靠硬件的軟件開發(fā)變成可能。并且,它能提供老練的查明故障和診斷器械的功能,提

70、供對(duì)機(jī)器的狀態(tài)的詳細(xì)分析,可能的故障起因,并且推薦補(bǔ)救措施。當(dāng)控制系統(tǒng)運(yùn)行時(shí)，你能使用現(xiàn)成的窗口軟件進(jìn)行數(shù)據(jù)分析?？刂葡到y(tǒng)和企業(yè)的其他部門之間傳遞信息使用標(biāo)準(zhǔn)窗口數(shù)據(jù)交換方法。</p><p>　　現(xiàn)在，個(gè)人計(jì)算機(jī)在工業(yè)控制中是成功的，其原因類似于那些PLC，今天工程師能很好的熟練的在計(jì)算機(jī)中編程并且應(yīng)用。許多站已經(jīng)有專業(yè)的個(gè)人計(jì)算機(jī)編程的技術(shù)在手。并且,典型的個(gè)人計(jì)算機(jī)語言范例易于使用流程圖編制技術(shù)和流程表新發(fā)

71、展技術(shù)對(duì)控制編程,譬如連續(xù)函數(shù)圖。</p><p>　　商用的個(gè)人計(jì)算機(jī)通常沒設(shè)計(jì)抗干擾、振動(dòng)、溫度和制造業(yè)中常發(fā)生的電子噪聲。在PLC和個(gè)人計(jì)算機(jī)中的,應(yīng)該用 能適應(yīng)這些環(huán)境狀況的硬件，這也許會(huì)增加基于個(gè)人計(jì)算機(jī)的控制的費(fèi)用。個(gè)人計(jì)算機(jī)以其少數(shù)I/O接點(diǎn)，不能在應(yīng)用中有效的控制成本。因此非常便宜的PLC能占領(lǐng)市場（90%的市場）。對(duì)于有許多I/O 點(diǎn)和復(fù)雜控制策略的控制系統(tǒng)，個(gè)人計(jì)算機(jī)可以形象地給出解答?；趥€(gè)