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人計算機在過程控制中的對比</p><p><b>　　工業(yè)工程部門</b></p&

53、gt;<p><b>　　波多里哥大學</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,個人計算機(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)應用上。與PLC 的使用有關的基本概念可由繼電控制板的動作來解釋。這使基于標準個人計算機建立一個簡單的模型，能和基于PLC的一樣。本文列舉了一個使用自動化過程的簡單的例子,樣品代碼會由一種標準高級語言提出，這種高級語言可能被用作為模板。最后,提出了使用個人計算機做過程控制的潛在的好處和一些改進措施。</p><p>　　主題詞: 可編程序控制器, 個人計算機, 自動化, 梯形圖, 繼電控制

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

56、裝置可能包括螺線管,馬達起始者,和一些其它相關的設備。圖1顯示了一種工業(yè)應用的一個簡化的模型，該模型中 PLC 得到應用。</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用。因為復雜系統(tǒng),它們的造價高，很難重新構造,出現(xiàn)故障也不容易發(fā)現(xiàn),消耗許多能量,適當?shù)牟僮魉俣?和低可靠性。在要求維護靈活、方便，而且又要快速查明故障

57、的復雜工業(yè)應用中，繼電控制板不是最適當?shù)倪x擇。另一方面,他們相對地易學，容易被電工和非工程學人員了解。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,但強調各條電路的作用。他們實質上代表一個被硬聯(lián)線的節(jié)目控制操作，序列在一個指定的過程中的一套并聯(lián)電路。電子電路的平行設計為解決所有控制邏輯帶來好處，可以同時和瞬間動作。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是典型地計算機為主的,不用真空管的,與梯形圖的動作一致的唯一處理器設備。因為他們是連續(xù)機器,實時地反應并聯(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構，它存儲關于當前的掃描周期的所有的相關的信息。它被細分為三種基本的部分:輸入表,輸出表,和

59、內部繼電表,輸入(傳感器的)狀態(tài)被保留在輸入表;輸出(傳動裝置)期待狀態(tài)被保留在輸出表;真正控制繼電器的狀態(tài)被保留在內部繼電表中。</p><p>　　圖3 PLC掃描周期</p><p>　　當程序是在PLC中運行，它連續(xù)的執(zhí)行掃描周期(圖 3)。掃描周期有二大部分(在實際PLC中，它有其它部分，這里只討論相關的):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。程序掃描解決布爾邏輯，它關系到在輸入表的信息,在輸出和內部繼電表的信息。而且,信息在輸出和內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，目前是被廣泛應用的工業(yè)自動化控制器。因為它們的語言，在它們的介紹之時它們是非常成功的，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比較，也有它們自己的一些缺點。它的局限有:它們是沒有工業(yè)標準的硬件或軟件平臺,它們會限制程序員 做的控制活動和操作,并且

62、為了降低成本，它的計算能力相對低。</p><p><b>　　個人計算機</b></p><p>　　標準個人計算機(個人計算機) ，一種為達到同樣目的的其它技術。它變得越來越普遍。在任一種工業(yè)控制應用中,一個基于個人計算機的控制器模型能替換PLC?？赡軙谲浖_發(fā)領域會開辟一個世界，因為它的標準組分和連通性。這個模型包括一臺能運行在任一個現(xiàn)代開放操作系統(tǒng)的標準個人

63、計算機, 一套等效于典型的PLC中的輸入模塊的標準輸入產品模塊, 還有用于實施一個PLC 掃描周期的任一種高級編程語言。</p><p><b>　　一個簡單的例子</b></p><p>　　提出的模型將通過一個抽樣程序被編碼在Turbo Pascal ，作為過程的控制，如圖1所示. 假設, 傳感器通過輸入端十六進制地址3BD被連接到個人計算機, 并且, 傳動裝置被

64、連接到輸出端口十六進制地址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。當這些變量是真的,那代表開狀態(tài);而當他們是假

65、的,代表關狀態(tài)。當交換信號以輸入和輸出指向開狀態(tài)代表一邏輯"0" 而關狀態(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，以使個人計算機結合標準程序高級語言編程。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，沒有考慮一個特殊操作系統(tǒng)的復雜，而且控制一個簡單的方式。這說明,復雜的自定義軟件不一定要做這項技術工作。</p><p>　　提出的模型非常容易適應和實施，因為它仍然使用梯形邏輯,那么就不一定要新技術。所有典型的PLC 指示可以非常容易地增加到模型,包括定時器,計數(shù)器 等等。其它的適合于特殊應用的PLC可能包括使用高級語言，這又使它比標準PLC 梯形邏輯強有力。</p><p>

67、<b>　　個人計算機的優(yōu)點</b></p><p>　　個人計算機是標準硬件軟件平臺。個人計算機以快速步伐改善,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，個人計算機勝過最快速的PLC 近20:1甚至更多。每六個到九個月，個人計算機就更新?lián)Q代。相反每二到三年PLC 硬件更新一次。至少的在個人計算機中，16Mbytes是普遍的, 同時PLC仍然的記憶區(qū)是按Kbyte 的順

68、序。個人計算機支持更加標準的外圍設備，譬如大容量只讀存儲器驅動器,聲卡,鼠標,網(wǎng)絡設施,等等，可從許多販賣者以合適的價格買到。通過許多販賣者，個人計算機是在短時間內在全世界廣泛使用。</p><p>　　有人構想,下一代工業(yè)控制應該提供一個開放式體系結構和一個唯一軟件開發(fā)環(huán)境。 趨向將是走出封閉,專有系統(tǒng)依賴一個開放式體系結構提供的好處。用戶必須和一個特殊供應商"結婚" ，這提供了更多的靈活性

69、。，因為許多獨立開發(fā)商連續(xù)推進個人計算機，這些計算機兼容硬件和軟件的功能，且易用，這使得對新的技術的掌握變的更加的容易,因為計算機的巨大的市場，它提供一個競爭環(huán)境，而且經(jīng)濟的原因驅使廠商們將價格壓到最低，因此成本效率高。</p><p>　　個人計算機可能提供合并PLC的一種完全解決方案,基于人機接口和編程的終端。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、供對機器的狀態(tài)的詳細分析,可能的故障起因,并且推薦補救措施。當控制系統(tǒng)運行時，你能使用現(xiàn)成的窗口軟件進行數(shù)據(jù)分析。控制系統(tǒng)和企業(yè)的其他部門之間傳遞信息使用標準窗口數(shù)據(jù)交換方法。</p><p>　　現(xiàn)在，個人計算機在工業(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算機中編程并且應用。許多站已經(jīng)有專業(yè)的個人計算機編程的技術在手。并且,典型的個人計算機語言范例易于使用流程圖編制技術和流程表新發(fā)

71、展技術對控制編程,譬如連續(xù)函數(shù)圖。</p><p>　　商用的個人計算機通常沒設計抗干擾、振動、溫度和制造業(yè)中常發(fā)生的電子噪聲。在PLC和個人計算機中的,應該用 能適應這些環(huán)境狀況的硬件，這也許會增加基于個人計算機的控制的費用。個人計算機以其少數(shù)I/O接點，不能在應用中有效的控制成本。因此非常便宜的PLC能占領市場（90%的市場）。對于有許多I/O 點和復雜控制策略的控制系統(tǒng)，個人計算機可以形象地給出解答?；趥€