外文翻譯---離散系統(tǒng)和z變換

1、<p><b>　　外文資料</b></p><p>　　Discrete-time Systems and the z-Transform Method</p><p>　　Discrete-time systems, or sampled-data system, are dynamic systems in which one or more vari

2、ables can change only at discrete instants of time. These instants, which we shall denote by or (k=0,1,2,…) , may specify the time at which some physical measurement is performed or the time at which the memory of a dig

3、ital computer is read out, etc. The time interval between two discrete instants is taken to be sufficiently short so that the data for the time between these discrete instants can be appro</p><p>　　Discrete-

4、time systems differ from continuous-time ones in that the signals for a discrete-time system are in sample-data form. Discrete-time systems arise in practice whenever the measurements necessary for control are obtained i

5、n an intermittent fashion, or a large scale controller or computer is time-shared by several plants so that a control signal is sent out to each plant only periodically or whenever a digital computer is used to perform c

6、omputations necessary for control. Many modern indu</p><p>　　In this lesson, we shall be concerned with discrete-time systems which the signal representing the control efforts is piecewise constant and chang

7、es only at discrete points in time. Since there are several different types of sampling operation of practical importance, we shall list them as follows:</p><p>　　(1) Periodic (conventional) sampling: In thi

8、s case, the sampling instants are equally spaced, or (=1, 2, 3… )</p><p>　　(2) Multiple-order sampling: The pattern of theis repeated periodically, or =constant for all.</p><p>　　(3) Multiple-ra

9、te sampling: In this case, two concurrent sampling operations occur at =and, where, are constants and, are integers.</p><p>　　(4) Random sampling: In this case, the sampling instants are random, or tk is a r

10、andom variable.</p><p>　　Here we shall treat only the case which the sampling is periodic.</p><p>　　Quantization. The inclusion of digital computer in an otherwise analog system produces in digi

11、tal form (usually as binary numbers) in part of the system. The system then takes the form of a mixed digital–analog combination. The introduction of a digital computer in a control system requires the use of digital-to-

12、analog and analog-to-digital converters. The conversion of an analog signal to the corresponding digital signal (binary number) is an approximation because the analog signal can take an </p><p>　　The process

13、 of quantizing (converting a signal in analog form to digital form) may be fulfilled by means of some specific circuits. The range of input magnitudes is divided into a finite number of disjoint intervals which are not

14、necessarily equal. All magnitudes falling within each interval are equated to a single value within the interval. This single value is the digital approximation to the magnitudes of the analog input signal. Thus, if x is

15、 the analog input, the digital output is given by</p><p>　　Transducer. A transducer is a device which converts an input signal into an output signal of another form. (The output signal, in general, depends o

16、n the past history of the input).</p><p>　　Analog transducer. An analog transducer is a transducer in which the input and output signals are continuous functions of time. The magnitudes of these signals may

17、be any value within the physical limitations of the system.</p><p>　　Sampled-data transducer. This is a transducer in which the input and output signals occur only at discrete instants of time (usually perio

18、dic) , but the magnitudes of the signal, as in the case of the analog transducer, are unquantized.</p><p>　　Digital transducer. A digital transducer is one in which the input and output signals occur only at

19、 discrete instants of time, and the signal magnitudes are quantized. i.e., they can assume only certain discrete levels.</p><p>　　Analog-to-digital transducer. This is a transducer in which the input signal

20、is a continuous function of time and the output signal is a quantized signal which can assume only certain discrete levels.</p><p>　　Digital-to-analog transducer. A digital-to-analog transducer is one in whi

21、ch the input signal is a quantized signal and the output signal is a smoothed continuous function of time.</p><p>　　Analog controllers and digital controllers. In considering the types of controllers which a

22、re used in industrial control system, we may divide them into the following three categories:</p><p>　　Analog controllers or computers: Analog controllers or computers represent the variables in the equation

23、s by continuous physical quantities. Analog controllers can be designed which will satisfactorily serve as non decision making controllers.</p><p>　　Digital controllers or computers: These operate only on nu

24、mbers. Decision-making is an important function in digital controllers, and they are currently being used for the solution of problems involving the optimal overall operation of industrial plants.</p><p>　　A

25、nalog-digital controllers or computers: These are often called hybrid controllers. They are combinations of analog controllers and digital controllers. Some of the high performance controllers are of this type.</p>

26、<p>　　Advantages of digital controllers over analog controllers. Some of the advantages of digital controllers over analog controllers may be summarized as follows:</p><p>　　(1) Digital controllers ar

27、e capable of performing complex computations with constant accuracy at high speed. Digital computers can have almost any desired accuracy in computations at relatively little increase in cost. On the other hand, the cost

28、 of analog computers increases rapidly as the complexity of the computations increase if constant accuracy is to be maintained.</p><p>　　(2) Digital controllers are extremely versatile. By merely issuing a n

29、ew program, one can completely change the operations being performed. This feature is particularly important if the control system is to receive operating information or instructions from some computing center, where eco

30、nomic analysis and optimization studies are being made.</p><p>　　Because of the inability of conventional techniques to adequately handle complex control problems, it has been customary to subdivide a proces

31、s into smaller units and handle each of these as a separate control problem. Human operators are normally used to coordinate the operation of units. Recent advances in computer control systems have caused changes in this

32、 use of industrial process controls. Recent developments in large-scale computers and mathematical methods provide a basis for use of all </p><p>　　Computer control of complex systems. Current trends in the

33、control of large-scale systems are to consolidate the multiplicity of independently controlled units into single optimally controlled processes. In industrial process control system, it is, in general, not practical to o

34、perate for a very long time at steady state because certain changes in production requirements, raw materials, economic factors, and processing equipment and techniques, may occur. Thus, the transient behavior of industr

35、i</p><p>　　Note that a system capable of controlling a process as completely as possible will have to solve complex equations. The more complete the control, the more important it is that the correct relatio

36、ns between operating variables be known and be used. The system must be capable of accepting instructions from such varied sources as computers and human operators and must also be capable of changing its control subsyst

37、em completely in a short time.</p><p>　　z-transform approach and state-space approach to the analysis of discrete-time systems. The analysis of discrete-time system may be carried out easily in either of two

38、 different approaches. One is the z-transform approach and the other is the state-space approach.</p><p>　　The z-transform approach has the same relationship to linear time-invariant discrete-time systems as

39、 the Laplace transform approach bears to liner time-invariant continuous-time systems. This section presents only the z-transform approach to the analysis of linear time-invariant discrete-time system.</p><p&g

40、t;　　TCP/IP INTRODUCTION</p><p>　　When you configure the TCP/IP protocol on a Microsoft Windows computer, an IP address, subnet mask, and usually a default gateway are required in the TCP/IP configuration set

41、tings.</p><p>　　To configure TCP/IP correctly, it is necessary to understand how TCP/IP networks are addressed and divided into networks and subnetworks. This article is intended as a general introduction to

42、 the concepts of IP networks and subnetting. A glossary is included at the end of article.</p><p>　　The success of TCP/IP as the network protocol of the Internet is largely because of its ability to connect

43、together networks of different sizes and systems of different types. These networks are arbitrarily defined into three main classes (along with a few others) that have predefined sizes, each of which can be divided into

44、smaller subnetworks by system administrators. A subnet mask is used to devided an IP addresses and subnet masks work, look at an IP (Internet Protocol) address and see how i</p><p>　　TCP services</p>

45、<p>　　Although the TCP and UDP are using the same network layer (IP), TCP has provided to the application layer and UDP completely different services.</p><p>　　TCP provides a connection-oriented, reliab

46、le stream of bytes services.</p><p>　　For the use of TCP connection means that two of the application (usually a client and a server) in the mutual exchange of data must be before the establishment of a TCP

47、connection. This process is very similar with the call, first dial-up ring, waiting for the other side pick said, “Hey,” Who is that before.</p><p>　　In a TCP connection, only two parities to communicate wit

48、h each other. Broadcast and Multicast can not be used for TCP.</p><p>　　TCP adoption of the following ways to provide reliability:</p><p>　　Application data Beifengecheng suited to TCP that sent

49、 most of the block. This is completely different from UDP, the application of the data on the length will remain the same. TCP from the information passed to the IP unit known as the text of the report or paragraph (segm

50、ent) TCP on how to determine the length of the text.</p><p>　　When the TCP send a paragraph later, it started a timer, wait for the end purpose of this newspaper that on receipt of the text. If not received

51、a confirmation in time, will be re-issued the text of the report. In Chapter 21 we will understand TCP protocol in the overtime and adaptive re-strategy.</p><p>　　When the TCP received from other side of the

52、 TCP connection data, it will send a confirmation. This confirmation is not sent immediately, usually a fraction of a second will be postponed.</p><p>　　TCP will maintain its first data and the testing and.

53、This is an end-to-end testing and to detect the transmission of data in the course of any changes. If you receive the test of the errors and, TCP will be discarded this message, and do not acknowledge receipt of this mes

54、sage (hope that both the originator of the overtime).</p><p>　　Since the TCP packet of data as reported to transmit IP, and IP data on the disorder may be reached, TCP packet of the disorder may also be reac

55、hed. If necessary, TCP will receive the data re-order, will receive the data to the correct sequence to the application layer.</p><p>　　Since the IP data will be reported duplication, TCP the receiving end m

56、ust be disposed of duplication of data.</p><p>　　IP addresses: Networks and hosts</p><p>　　An IP address is a 32-bit number that uniquely identifies a host (computer or other device, such as a p

57、rinter or router) on a TCP/IP network.</p><p>　　IP addresses are normally expressed in dotted-decimal formal, with four numbers separated by periods, such as 192.168.123.132. To understand how subnet masks a

58、re used to distinguish between hosts, networks, and subnetwoeks, examine an IP address in binarv notation.</p><p>　　For a TCP/IP wide area network (WAN) to work efficiently as a collection of networks, the r

59、outers that pass packets of data between networks do not know the exact location of a host for which a packet of information is destined. Routers only know what network the host is member of and use information stored in

60、 their route table to determine how to get the packet to the destination host’s network. After the packet is delivered to the destination’s network, the packet is delivered to the appropria</p><p><b>　

61、　譯文</b></p><p><b>　　離散系統(tǒng)和Z變換</b></p><p>　　離散系統(tǒng)或數(shù)據(jù)采樣系統(tǒng)是指一個或多個變量僅在離散的瞬時變化的動態(tài)系統(tǒng)。這些瞬時值可以用或表示，指完成測量的時間或者數(shù)字計算機內(nèi)存的讀取時間。兩個離散時刻的間隔取得很短，這樣離散時刻之間的數(shù)據(jù)就可以用簡單的插值法近似。</p><p>　　離散系

62、統(tǒng)不同于連續(xù)系統(tǒng)，它的信號是采樣數(shù)據(jù)形式。</p><p>　　在實際應用中，當控制所需要的測量以間斷的方式進行時，或者當大型的控制器或計算機被多個控制對象所共享，導致傳送到每一個控制對象去的控制信號僅為周期性信號時，或者在采用數(shù)字計算機去完成控制所必需的計算時，就會產(chǎn)生離散系統(tǒng)。許多現(xiàn)代工業(yè)控制系統(tǒng)都是離散的，因為它們總是包含一些輸入/輸出量在時間上是離散的器件。當然，采樣操作或離散化有時完全是假設，其引進目的

63、僅僅是為了簡化實際上只包含連續(xù)性元件的控制系統(tǒng)的分析。</p><p>　　在本課中，我們將討論作為控制作用的信號是斷續(xù)的常量離散系統(tǒng)，且該常量僅在離</p><p>　　散的時間點上變化。因為存在幾種不同類型且有實用價值的采樣運算，我們就將它們列舉如下：</p><p>　　(1) 周期(普通)采樣：采樣時刻的間隔相等，即(k=1,2,3) 。</p>

64、<p>　　(2) 多級采樣：在形式上周期性地出現(xiàn)，即對于所有的,常量。</p><p>　　(3) 多速采樣：兩個同時進行的采樣操作分別發(fā)生在和。其中p、q 是整數(shù)，、是常數(shù)。</p><p>　　(4) 隨機采樣：采樣時刻是隨機的，即是隨機變量。</p><p>　　這里我們只討論周期采樣的情況。</p><p>　　量化

65、當模擬系統(tǒng)中包含數(shù)字計算機時，系統(tǒng)的某一部分就產(chǎn)生數(shù)字形式的信號(通常是二進制數(shù))。因此，系統(tǒng)就呈現(xiàn)出數(shù)字-模擬式的混合結構形式。在控制系統(tǒng)中引入數(shù)字計算機，就要使用數(shù)模和模數(shù)轉換器。因為模擬信號具有無窮多的數(shù)值，而由一組確定的數(shù)值表示數(shù)的數(shù)量是有限的，所以，模擬信號轉換為相應的數(shù)字信號(二進制數(shù))是一種近似。這種近似過程稱為量化。</p><p>　　量化的過程(將模擬量轉化為數(shù)字量)由一些特定的電路來完成。輸

66、入量的幅值范圍被分為許多有限的區(qū)間,不一定相等。一個區(qū)間的所有幅值都取區(qū)間內(nèi)的唯一值。這個唯一的值就是對模擬輸入信號幅度的數(shù)字近似。因此，如果為模擬輸入，輸出的數(shù)字值就由確定，其中為量化函數(shù)。</p><p>　　函數(shù)是一個離散信號。數(shù)字控制系統(tǒng)的操作包括幅值和時間的量化。下面我們介紹一些術語的定義。</p><p>　　轉換器：轉換器是將輸入信號轉換為另一種形式輸出的裝置(輸出信號通常取

67、決于輸入信號的歷史值)。</p><p>　　模擬轉換器：模擬轉換器是輸入和輸出信號都是時間的連續(xù)函數(shù)的轉換器。這些信號可以取系統(tǒng)物理限制范圍內(nèi)的任意值。</p><p>　　采樣數(shù)據(jù)轉換器：采樣數(shù)據(jù)轉換器是輸入和輸出信號只在離散的瞬間出現(xiàn)的轉換器，并且其幅值和模擬轉換器的情況一樣，未被量化。</p><p>　　數(shù)字轉換器：數(shù)字轉換器是輸入和輸出信號只在離散的瞬間

68、出現(xiàn)的轉換器，其幅值是被量化了的，即信號只取特定的離散值。</p><p>　　模擬-數(shù)字轉換器：模擬-數(shù)字轉換器的輸入信號是連續(xù)信號，而輸出信號則為量化信號，而且只取特定的離散值。</p><p>　　數(shù)字-模擬轉換器：數(shù)字-模擬轉換器的輸入信號為量化信號，而輸出信號為時間的平滑連續(xù)函數(shù)。</p><p>　　模擬控制器和數(shù)字控制器 就工業(yè)控制系統(tǒng)中采用的控制器類

69、型而言，我們可以將它們分為以下3 類：</p><p>　　模擬控制器或計算機：模擬控制器或計算機是用連續(xù)的物理量表示方程中的變量。模擬控制器可以設計為令人滿意的非決策控制器。</p><p>　　數(shù)字控制器或計算機：它們僅對數(shù)字進行操作。決策是數(shù)字控制器的一個重要功能，并常用它們來解決工業(yè)對象中總體運行的優(yōu)化問題。</p><p>　　模擬數(shù)字控制器或計算機：它們

70、通常被稱為混合控制器，是模擬控制器和數(shù)字控制器的一種組合。一些高性能控制器屬于這種類型。</p><p>　　數(shù)字控制器相對于模擬控制器的優(yōu)點 數(shù)字控制器相對于模擬控制器的優(yōu)點可以總結如下：</p><p>　　(1) 數(shù)字控制器能以一定精度高速地完成復雜的運算。在運算中，數(shù)字計算機能在增加較少成本的情況下實現(xiàn)希望的精度。但是，若保持精度不變，運算越復雜，模擬計算機的成本也就越高。<

71、/p><p>　　(2) 數(shù)字控制器具有很好的通用性。僅僅更新一段程序，就能改變現(xiàn)有操作。如果控制系統(tǒng)接收進行經(jīng)濟分析和優(yōu)化研究的計算中心發(fā)出的操作信息或指令時，這種優(yōu)點就尤為重要了。</p><p>　　傳統(tǒng)的方法不能處理復雜的控制問題，所以它通常是將過程細分為更小的單元，然后分別作為獨立的控制問題來處理。人工操作員通常用于協(xié)調(diào)多個單元的操作。近來，隨著計算機控制系統(tǒng)的發(fā)展，改變了工業(yè)過程控

72、制的這種狀況。大型計算機和數(shù)學方法的發(fā)展為控制系統(tǒng)中利用所有有用信息奠定了基礎。傳統(tǒng)控制中的這部分控制回路由人工完成。</p><p>　　復雜系統(tǒng)的計算機控制 大規(guī)模系統(tǒng)控制當前的發(fā)展趨勢是將多個獨立控制單元合并為一個最優(yōu)的控制過程。一般來說，由于產(chǎn)品需求、原材料、經(jīng)濟因素、加工設備和方法的變化，工業(yè)過程控制系統(tǒng)并不能長時間工作于固定的狀態(tài)。因此，我們必須考慮工業(yè)過程中的動態(tài)特性。因為過程變量之間相互影響，所以

73、，每個控制單元只采用一個過程變量，對于真正的全面控制來說是不適當?shù)?。通過使用計算機，可以將所有過程變量和經(jīng)濟因素、產(chǎn)品要求、設備性能等都考慮在內(nèi)，實現(xiàn)工業(yè)過程的最優(yōu)控制。</p><p>　　值得一提的是，一個盡可能全面地控制過程的系統(tǒng)必須能解復雜的方程。越是全面的控制，了解和應用操作變量之間的正確關系就越重要。系統(tǒng)必須能接收諸如計算機和操作員這樣的不同信號源所發(fā)出的指令，并且能在短時間內(nèi)改變其控制的子系統(tǒng)。&l

74、t;/p><p>　　離散系統(tǒng)分析的Z 變換法和狀態(tài)空間法 離散系統(tǒng)的分析可以很容易采用Z 變換法和狀態(tài)空間法中的任一種。</p><p>　　Z 變換與線性定常離散系統(tǒng)的關系，就像是拉氏變換與線性定常連續(xù)系統(tǒng)的關系一樣。這部分只介紹線性時不變離散系統(tǒng)的Z 變換法。</p><p><b>　　TCP/IP介紹</b></p><

75、;p>　　在Microsoft Windows計算機上配置TCP/IP協(xié)議時，TCP/IP配置設置中需要IP地址和子網(wǎng)掩碼，通常還需要一個默認網(wǎng)關。</p><p>　　要正確配置TCP/IP,有必要了解TCP/IP網(wǎng)絡的尋址方式以及網(wǎng)絡和子網(wǎng)的劃分方式。本文旨在對IP網(wǎng)絡和子網(wǎng)的概念進行一般性介紹。</p><p>　　作為Internet的網(wǎng)絡協(xié)議，TCP/IP的成功在很大程度上

76、歸功于它將不同大小的網(wǎng)絡和不同類型的系統(tǒng)連接在一起的能力。這些網(wǎng)絡被強制定義為具有預定義大小的三個主要類（還有其他一些類別），每一類都可以由系統(tǒng)管理員分成更小的子網(wǎng)。子網(wǎng)掩碼用于將IP地址分成兩個部分。一部分標識主機（計算機），另一部分標識它所屬的網(wǎng)絡。查看IP（Internet協(xié)議）地址并研究它的組織方式可以幫助您更好地理解IP地址和子網(wǎng)掩碼的工作方式。</p><p><b>　　TCP的服務<

77、;/b></p><p>　　盡管TCP和UDP都使用相同的網(wǎng)絡層（IP），TCP卻向應用層提供與UDP完全不同的服務。</p><p>　　TCP提供一種面向連接的、可靠地字節(jié)流服務。</p><p>　　面向連接意味著兩個使用TCP的應用（通常是一個客戶和一個服務器）在彼此交換數(shù)據(jù)之前必須先建立一個TCP連接。這一過程與打電話很相似，先撥號振鈴，等待對方摘

78、機說“喂”，然后才說明是誰。</p><p>　　在一個TCP連接中，僅有兩方進行彼此通信。廣播和多播不能用于TCP。TCP用過下列方式來提供可靠性：</p><p>　　應用數(shù)據(jù)被分割成TCP認為最合適發(fā)送的數(shù)據(jù)塊。這和UDP完全不同，應用程序產(chǎn)生的數(shù)據(jù)報長度將保持不變。由TCP傳遞給IP的信息單位稱為報文段或段（segment）TCP如何確定報文段的長度。</p><

79、;p>　　當TCP發(fā)出一個段后，它啟動一個定時器，等待目的端確認收到這個報文段。如果不能及時收到一個確認，將重發(fā)這個報文段。</p><p>　　當TCP收到發(fā)自TCP連接另一端的數(shù)據(jù)，他將發(fā)送一個確認。這個確認不是立即發(fā)送，通常將推遲幾分之一秒。</p><p>　　TCP將保持它首部和數(shù)據(jù)的檢驗和。這是一個端到端的檢驗和，目的是檢測數(shù)據(jù)在傳輸過程中的任何變化。如果收到段的檢驗和有

80、差錯，TCP將丟棄這個報文段和不確認收到此報文段（希望發(fā)端超時并重發(fā)）。</p><p>　　既然TCP報文段作為IP數(shù)據(jù)報來傳輸，而IP數(shù)據(jù)報的到達可能會失序，因此TCP報文段的到達也可能會失序。如果必要，TCP將對收到的數(shù)據(jù)進行重新排序，將收到的數(shù)據(jù)以正確的順序交給應用層。</p><p>　　既然IP數(shù)據(jù)報會發(fā)生重復，TCP的接收端必須丟棄重復的數(shù)據(jù)。</p><

81、p>　　IP地址：網(wǎng)絡和主機</p><p>　　IP地址是一個32位數(shù)字，它唯一地標識TCP/IP網(wǎng)絡上的主機（計算機或其他設備，如打印機或路由器）。</p><p>　　IP地址通常以點分十進制格式表示，四個數(shù)字由句點分隔，例如192.168.123.132。要了解子網(wǎng)掩碼如何用于區(qū)分不同的主機、網(wǎng)絡和子網(wǎng)，請查看以二進制表示的IP地址。</p><p>