電氣工程及其自動(dòng)化專業(yè)英語(yǔ)第一章課文翻譯

1、精選優(yōu)質(zhì)文檔-傾情為你奉上第一章第一篇sectiongTwo variables u(t) and i(t) are the most basic concepts in an electric circuit, they characterize the various relationships in an electric circuitu(t)和i(t)這兩個(gè)變量是電路中最基本的兩個(gè)變量，它們刻劃了電路的各種關(guān)系。Charge and Current The concept of electric charge is the underlying principle for expla

2、ining all electrical phenomena. Also, the most basic quantity in an electric circuit is the electric charge. Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). 電荷和電流 電荷的概念是用來(lái)解釋所有電氣現(xiàn)象的基本概念。也即，電路中最基本的量是電荷。電荷是構(gòu)成物質(zhì)的原子微粒的電氣屬性，它是以庫(kù)侖為單位來(lái)度量的。We know

3、from elementary physics that all matter is made of fundamental building blocks known as atoms and that each atom consists of electrons, protons, and neutrons. We also know that the charge e on an electron is negative and equal in magnitude to ×1019C, while a proton carries a positive charge of

4、the same magnitude as the electron. The presence of equal numbers of protons and electrons leaves an atom neutrally charged. 我們從基礎(chǔ)物理得知一切物質(zhì)是由被稱為原子的基本構(gòu)造部分組成的，并且每個(gè)原子是由電子，質(zhì)子和中子組成的。我們還知道電子的電量是負(fù)的并且在數(shù)值上等于×10-12C，而質(zhì)子所帶的正電量在數(shù)值上與電子相等。質(zhì)子和電子數(shù)量相同使得原子呈現(xiàn)電中性。We consider the flow of electric charges. A unique f

5、eature of electric charge or electricity is the fact that it is mobile; that is, it can be transferred from one place to another, where it can be converted to another form of energy讓我們來(lái)考慮一下電荷的流動(dòng)。電荷或電的特性是其運(yùn)動(dòng)的特性，也就是，它可以從一個(gè)地方被移送到另一個(gè)地方，在此它可以被轉(zhuǎn)換成另外一種形式的能量。When a conducting wire is connected to a battery

6、(a source of electromotive force), the charges are compelled to move; positive charges move in one direction while negative charges move in the opposite direction. This motion of charges creates electric current. It is conventional to take the currentflow as the movement of positive charges, that is

7、, opposite to the flow of negative charges, as illustrates. This convention was introduced by Benjamin Franklin (l706l790), the American scientist and inventor. Although we now know that current in metallic conductors is due to negatively charged electrons, we will follow the universally accepted co

8、nvention that current is the net flow of positive charges. Thus, Electric current is the time rate of charge, measured in amperes (A). Mathematically, the relationship among current i, charge q, and time t is 當(dāng)我們把一根導(dǎo)線連接到某一電池上時(shí)(一種電動(dòng)勢(shì)源)，電荷被外力驅(qū)使移動(dòng)；正電荷朝一個(gè)方向移動(dòng)而負(fù)電荷朝相反的方向移動(dòng)。這種電荷的移動(dòng)產(chǎn)生了電流。我們可以很方便地把電流看作是正電荷的移

9、動(dòng)，也即，與負(fù)電荷的流動(dòng)方向相反，如圖11所示。這一慣例是由美國(guó)科學(xué)家和發(fā)明家本杰明富蘭克林引入的。雖然我們現(xiàn)在知道金屬導(dǎo)體中的電流是由負(fù)電荷引起的，但我們將遵循通用的慣例，即把電流看作是正電荷的單純的流動(dòng)。于是電流就是電荷的時(shí)率，它是以安培為單位來(lái)度量的。從數(shù)學(xué)上來(lái)說(shuō)，電流i、電荷q以及時(shí)間t之間的關(guān)系是： The charge transferred between time t0 and t is obtained by integrating both sides of Eq. (1-1). We obtain從時(shí)間t0到時(shí)間t所移送的電荷可由方程（11）兩邊積分求得。我們算得：The

10、 way we define current as i in Eq. (1-l) suggests that current need not be a constant-valued function, charge can vary with time in several ways that may be represented by different kinds of mathematical functions我們通過(guò)方程（11）定義電流的方式表明電流不必是一個(gè)恒值函數(shù)，電荷可以不同的方式隨時(shí)間而變化，這些不同的方式可用各種數(shù)學(xué)函數(shù)表達(dá)出來(lái)。電壓，能量和功率 To move the

11、 electron in a conductor in a particular direction requires some work or energy transfer. This work is performed by an external electromotive force (emf), typically represented by the battery in . This emf is also known as voltage or potential difference. The voltage uab between two points a and b i

12、n an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically 在導(dǎo)體中朝一個(gè)特定的方向移動(dòng)電荷需要一些功或者能量的傳遞，這個(gè)功是由外部的電動(dòng)勢(shì)來(lái)完成的。圖11所示的電池就是一個(gè)典型的例子。這種電動(dòng)勢(shì)也被稱為電壓或電位差。電路中a、b兩點(diǎn)間的電壓等于從a到b移動(dòng)單位電荷所需的能量（或所需做的功）。數(shù)學(xué)表達(dá)式為：where w is energy in joules (J) and q is charge in coulombs (C). The volt

13、age uab is measured in volts (V), named in honor of the Italian physicist Alessandro Antonio Volta (l745l827), who invented the first voltaic battery. Thus, Voltage (or potential difference) is the energy required to move a unit charge through an element, measured in volts (V). 式中w是單位為焦耳的能量而q是單位為庫(kù)侖的

14、電荷。電壓Uab是以伏特為單位來(lái)度量的，它是為了紀(jì)念意大利物理學(xué)家Alessandro Antonio Volta而命名的，這位意大利物理學(xué)家發(fā)明了首個(gè)伏達(dá)電池。于是電壓（或電壓差）等于將單位電荷在元件中移動(dòng)所需的能量，它是以伏特為單位來(lái)度量的。 shows the voltage across an element (represented by a rectangular block ) connected to points a and b. The plus (+) and minus (-) signs are used to define reference direction o

15、r voltage polarity. The uab can be interpreted in two ways: point a is at a potential of uab volts higher than point b; the potential at point a with respect to point b is uab. It follows logically that in general 圖12顯示了某個(gè)元件（用一個(gè)矩形框來(lái)表示）兩端a、b之間的電壓。正號(hào)（）和負(fù)號(hào)（）被用來(lái)指明參考方向或電壓的極性，Uab可以通過(guò)以下兩種方法來(lái)解釋。1）在Uab伏特的電位中

16、a點(diǎn)電位高于b點(diǎn)，2）a點(diǎn)電位相對(duì)于b點(diǎn)而言是Uab，通常在邏輯上遵循Although current and voltage are the two basic variables in an electric circuit, they are not sufficient by themselves. For practical purposes, we need to know power and energy. To relate power and energy to voltage and current, we recall from physics that power is

17、 the time rate of expending or absorbing energy, measured in watts (W). We write this relationship as 雖然電流和電壓是電路的兩個(gè)基本變量，但僅有它們兩個(gè)是不夠的。從實(shí)際應(yīng)用來(lái)說(shuō)，我們需要知道功率和能量。為了把功率和能量同電壓、電流聯(lián)系起來(lái)，我們重溫物理學(xué)中關(guān)于功率是消耗或吸收的能量的時(shí)率，它是以瓦特為單位來(lái)度量的。我們把這個(gè)關(guān)系式寫(xiě)成：Where p is power in watts (W), w is energy in joules (J), and t is time in secon

18、ds (s). From Eq. (1-1), Eq. (1-3), and Eq. (1-5), it follows that 式中p是以瓦特為單位的功率，w是以焦耳為單位的能量，t是以秒為單位的時(shí)間，從方程（11）、（13）和（15）可以推出Because u and i are generally function of time, the power p in Eq. (1-6) is a time-varying quantity and is called the instantaneous power. The power absorbed or supplied by an

19、element is the product of the voltage across the element and the current through it. If the power has a plus sign, power is being delivered to or absorbed by the element. If, on the other hand, the power has a minus sign, power is being supplied by the element. But how do we know when the power has

20、a negative or a positive sign由于u和i通常是時(shí)間的函數(shù)，方程（16）中的功率p是個(gè)時(shí)間變量于是被稱為瞬時(shí)功率，某一元件吸收或提供的功率等于元件兩端電壓和通過(guò)它的電流的乘積。如果這個(gè)功率的符號(hào)是正的，那么功率向元件釋放或被元件吸收。另一方面，如果功率的符號(hào)是負(fù)的，那么功率是由元件提供的。但我們?nèi)绾蔚弥螘r(shí)功率為正或?yàn)樨?fù)Current direction and voltage polarity play a major role in determining the sign of power. It is therefore important that we p

21、ay attention to the relationship between current i and voltage u in (a). The voltage polarity and current i direction must conform with those shown in (a) in order for the power to have a positive sign. This is known as the passive sign convention. By the passive sign convention, current enters thro

22、ugh the positive polarity of the voltage. In this case, p = ui or ui 0 implies that the element is absorbing power. However, if p = -ui or ui 0, as in (b), the element is releasing or supplying power. 在我們確定功率符號(hào)時(shí)，電流的方向和電壓的極性起著主要的作用，這就是我們?cè)诜治鰣D13（a）所顯示的電流i和電壓u的關(guān)系時(shí)特別謹(jǐn)慎的重要原因。為了使功率的符號(hào)為正，電壓的極性和電流的方向必須與圖13（a

23、）所示的一致。 這種情況被稱為無(wú)源符號(hào)慣例，對(duì)于無(wú)源符號(hào)慣例來(lái)說(shuō)，電流流進(jìn)電壓的正極。在這種情況下，pui或ui>0，表明元件是在吸收功率。而如果pui或ui<0，如圖13（b）所示時(shí)，表明元件是在釋放或提供功率。In fact, the law of conservation of energy must be obeyed in any electric circuit. For this reason, the algebraic sum of power in a circuit, at any instant of time, must be zero事實(shí)上，在任何電路中

24、必須遵循能量守恒定律。由于這個(gè)原因，任一電路中在任何瞬間功率的代數(shù)和必須等于零This again confirms the fact that the total power supplied to the circuit must balance the total power absorbed. From Eq. (l-7), the energy absorbed or supplied by an element from time t0 to time t is這再一次證明了提供給電路的功率必須與吸收的功率相平衡這一事實(shí)。從方程（17）可知，從時(shí)間t0到時(shí)間t被元件吸收或由元件提供

25、的功率等于Section2An electric circuit is simply an interconnection of the elements. There are two types of elements found in electric circuits: passive elements and active elements. An active element is capable of generating energy while a passive element is not. Examples of passive elements are resistor

26、s, capacitors, and inductors. The most important active elements are voltage or current sources that generally deliver power to the circuit connected to them. 電路僅僅是元件之間的相互結(jié)合。我們發(fā)現(xiàn)電路中存在有兩種元件：無(wú)源元件和有源元件。有源元件能夠產(chǎn)生能量而無(wú)源元件卻不能，無(wú)源元件有電阻、電容和電感器等。最重要的有源元件是通常向與它們相連的電路釋放能量的電壓和電流源。Independent sources An ideal indep

27、endent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables.An independent voltage source is a two-terminal element, such as a battery or a generator, which maintains a specified voltage between its terminals. The voltage

28、is completely independent of the current through the element. The symbol for a voltage source having u volts across its terminals is shown in (a). The polarity is as shown, indicating that terminal a is u volts above terminal b. Thus if u > 0, then terminal a is at a higher potential than termina

29、l b. The opposite is true, of course, if u < 0 一個(gè)理想的獨(dú)立源是產(chǎn)生完全獨(dú)立于其它電路變量的特定電壓或電流的有源元件。一個(gè)獨(dú)立電壓源是一個(gè)二端口元件，如一個(gè)電池或一臺(tái)發(fā)電機(jī)，它們?cè)谄涠瞬烤S持某個(gè)特定的電壓。該電壓完全獨(dú)立于流過(guò)元件的電流，在其端部具有u伏電壓的電壓源的符號(hào)如圖14（a）所示，極性如圖所示，它表明a端比b端高u伏。如果u>0，那么a端的電位高于b端，當(dāng)然，如果u<0，反之亦然。In (a), the voltage u may be time varying, or it may be constant, in w

30、hich case we would probably label it U. Another symbol that is often used for a constant voltage source, such as a battery with U volts across its terminals, is shown in (b). In the case of constant sources we shall use (a) and 1-4(b) interchangeably.在圖14（a）中，電壓u可以是隨時(shí)間而變化，或者可以是恒定的，在這種情況下我們可能把它標(biāo)為U，對(duì)于

31、恒定電壓源我們通常使用另一種符號(hào)，例如在兩端只有U伏電壓的電池組，如圖14（b）所示。在恒定源的情況下我們可以交替地使用于圖14（a）或圖14（b）We might observe at this point that the polarity marks on (b) are redundant since the polarity could be defined by the positions of the longer and shorter lines. 我們可能已經(jīng)注意到這一點(diǎn)，即圖14（b）中的極性標(biāo)號(hào)，是多余的因?yàn)槲覀兛梢愿鶕?jù)長(zhǎng)天線的位置符，確定電池極性An independ

32、ent current source is a two-terminal element through which a specified current flows. The current is completely independent of the voltage across the element. The symbol for an independent current source is shown in , where i is the specified current. The direction of the current is indicated by the

33、 arrow一個(gè)獨(dú)立電流源是二端元件在兩端之間特定的電流流過(guò)，該電流完全獨(dú)立于元件兩端的電壓，一個(gè)獨(dú)立電流源的符合如圖15所示。圖中i是特定電流，該電流的方向由箭頭標(biāo)明Independent sources are usually meant to deliver power to the external circuit and not to absorb it. Thus if u is the voltage across the source and its current i is directed out of the positive terminal, then the sou

34、rce is delivering power, given by p = ui, to the external circuit. Otherwise it is absorbing power. For example, in (a) the battery is delivering 24 W to the external circuit. In (b) the battery is absorbing 24 W, as would be the case when it is being charged. 獨(dú)立源通常指的是向外電路釋放功率而非吸收功率，因此如果u是電源兩端的電壓而電流

35、i直接從其正端流出，那么該電源正在向?qū)﹄娐丰尫殴β?，由式pui算出。否則它就在吸收功率。例如圖16（a）中電池正在向外電路釋放功率24w，在圖16（b）中，電池就在充電情況，吸收功率24w。Dependent sources An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current. Dependent sources are usually designated by diamon

36、d-shaped symbols, as shown in the control of the dependent source is achieved by a voltage or current of some other element in the circuit, and the source can be voltage or current, it follows that there are four possible types of dependent sources, namely:（1）A voltage-controlled voltage source (VCV

37、S).（2）A current-controlled voltage source (CCVS).（3）A voltage-controlled current source (VCCS).（4）A current-controlled current source (CCCS). Dependent sources are useful in modeling elements such as transistors, operational amplifiers and integrated circuits. 一個(gè)理想的受控源是一個(gè)有源元件，它的電源量是由另外一個(gè)電壓和電流所控制。受控源

38、通常用菱形符號(hào)表明，如圖17所示。由于控制受控源的控制量來(lái)自于電路中其他元件的電壓或電流，同時(shí)由于受控源可以是電壓源或電流源。由此可以推出四種可能的受控源類型，即電壓控制電壓源（VCVS）電流控制電壓源（CCVS）電壓控制電流源（VCCS）電流控制電流源（CCCS）受控源在模擬諸如晶體管、運(yùn)算放大器以及集成電路這些元件時(shí)是很有用的It should be noted that an ideal voltage source (dependent or independent) will produce any current required to ensure that the termin

39、al voltage is as stated, whereas an ideal current source will produce the necessary voltage to ensure the stated current flow. Thus an ideal source could in theory supply an infinite amount of energy. It should also be noted that not only do sources supply power to a circuit, but they can absorb pow

40、er from a circuit too. For a voltage source, we know the voltage but not the current supplied or drawn by it. By the same token, we know the current supplied by a current source but not the voltage across it. 應(yīng)該注意的是：一個(gè)理想電壓源（獨(dú)立或受控）可向電路提供以保證其端電壓為規(guī)定值所需的任意電流，而電流源可向電路提供以保證其電流為規(guī)定值所必須的電壓。還應(yīng)當(dāng)注意的是電源不僅向電路提供功率

41、，他們也可從電路吸收功率。對(duì)于一個(gè)電壓源來(lái)說(shuō)，我們知道的是由其提供或所獲得的電壓而非電流，同理，我們知道電流源所提供的電流而非電流源兩端的電壓。第二章第一篇To say that we live in an age of electronics is an understatement. From the omnipresent integrated circuit to the equally omnipresent digital computer, we encounter electronic devices and systems on a daily basis. In every

42、 aspect of our increasingly technological society whether it is science, engineering, medicine, music, maintenance, or even espionagethe role of electronics is large, and it is growing.談?wù)撽P(guān)于我們生活在一個(gè)電子學(xué)時(shí)代的論調(diào)是一種空泛的論調(diào)。從無(wú)處不在的集成電路到同樣無(wú)處不在的數(shù)字計(jì)算機(jī)，我們?cè)谌粘；顒?dòng)中總會(huì)遇到電子設(shè)備和電子系統(tǒng)。在我們?nèi)找姘l(fā)展的科技社會(huì)的方方面面無(wú)論是在科學(xué)、工程、醫(yī)藥、音樂(lè)、維修方面甚至是在

43、諜報(bào)方面電子學(xué)的作用是巨大的，而且還將不斷增強(qiáng)。 In general, all of the tasks with which we shall be concerned can be classified as "signal-processing“tasks. Let us explore the meaning of this term一般說(shuō)來(lái)，我們將要涉及到的工作被歸結(jié)為“信號(hào)處理”工作，讓我們來(lái)探究這個(gè)術(shù)語(yǔ)的含義吧。A signal is any physical variable whose magnitude or variation with time contai

44、ns information. This information might involve speech and music, as in radio broadcasting, a physical quantity such as the temperature of the air in a room, or numerical data, such as the record of stock market transactions. The physical variables that can carry information in an electrical system a

45、re voltage and current. When we speak of "signals", therefore, we refer implicitly to voltages or currents. However, most of the concepts we discuss can be applied directly to systems with different information-carrying variables. Thus, the behavior of a mechanical system (in which force a

46、nd velocity are the variables) or a hydraulic system (in which pressure and flow rate are the variables) can often be modeled or represented by an equivalent electrical system. An understanding of the behavior of electrical systems, therefore, provides a basis for understanding a much broader range

47、of phenomena. 信號(hào)就是其與時(shí)間有關(guān)的量值或變化包含信息的任何物理變量。這種信息或許像無(wú)線電廣播的演講和音樂(lè)，或許是像室內(nèi)溫度的物理量，或許像股市交易記錄的數(shù)字?jǐn)?shù)據(jù)。在電氣系統(tǒng)中能夠載有信息的物理變量是電壓和電流。因此當(dāng)我們談到“信號(hào)”，我們不言而喻指的是電壓和電流，然而，我們要討論的大多數(shù)概念是可以被直接應(yīng)用于載有不同信息的變量的系統(tǒng)，因此，一個(gè)機(jī)械系統(tǒng)（在這個(gè)系統(tǒng)中力和速度是其變量）或者液壓系統(tǒng)（在這個(gè)系統(tǒng)中壓力和流速是其變量）的性能通常可以用一個(gè)等效的電氣系統(tǒng)來(lái)模擬或表示。因此，我們對(duì)于電氣系統(tǒng)性能的理解為理解更寬領(lǐng)域的現(xiàn)象打下了一個(gè)基礎(chǔ)。A signal can carry

48、 information in two different forms. In an analog signal the continuous variation of the voltage or current with time carries the information. An example, in , is the voltage produced by a thermocouple pair when the two junctions are at different temperatures. As the temperature difference between t

49、he two junctions varies, the magnitude of the voltage across the thermocouple pair also varies. The voltage thus provides an analog representation of the temperature difference. 一個(gè)信號(hào)可以以兩種形式來(lái)承載信息。在一個(gè)模擬信號(hào)中電壓或電流隨時(shí)間而產(chǎn)生的連續(xù)變化載有信息。在圖2-1中，當(dāng)一對(duì)熱電偶的接頭處于不同的溫度時(shí)由熱電偶所產(chǎn)生的電壓就是一個(gè)例子。當(dāng)兩個(gè)接頭之間的溫度差改變時(shí)，一對(duì)熱電偶兩端的電壓也將改變。于是電壓就

50、提供了溫度差的模擬表現(xiàn)形式The other kind of signal is a digital signal. A digital signal is one that can take on values within two discrete ranges. Such signals are used to represent ON-OFF or YES-NO information. An ordinary household thermostat delivers a digital signal tocontrol the furnace. When the room temp

51、erature drops below a preset value, the thermostat switch closes turning on the furnace. Once the room temperature rises high enough, the switch opens turning off the furnace. The current through the switch provides a digital representation of the temperature variation: ON equals "too cold"

52、; while OFF equals "not too cold". 另一種的信號(hào)是數(shù)字信號(hào)。數(shù)字信號(hào)是在兩個(gè)離散的范圍內(nèi)能夠呈現(xiàn)一定數(shù)值的信號(hào)。這種信號(hào)常用以表示“開(kāi)關(guān)”或“是不是”信息。一個(gè)普通的家用恒溫器傳遞一種數(shù)字信號(hào)來(lái)控制爐子當(dāng)房間的溫度下降到預(yù)定溫度以下時(shí)，恒溫器的開(kāi)關(guān)合上使?fàn)t子開(kāi)始加熱；一旦房間的溫度上升到足夠高，開(kāi)關(guān)就斷開(kāi)使?fàn)t子關(guān)閉。流過(guò)開(kāi)關(guān)的電流提供了溫度變化的數(shù)字表示：ON即為“太冷”而OFF即為“不太冷”A signal-processing system is an interconnection of components and devices

53、that can accept an input signal or a group of input signals, operate on the signals in some fashion either to extract or improve the quality of the information, and present the information as an output in the proper form at the proper time. 一個(gè)信號(hào)處理系統(tǒng)是某些元件或設(shè)備之間的相互連接，這些元件和設(shè)備能夠接收一個(gè)輸入信號(hào)或一組輸入信號(hào)，信號(hào)處理系統(tǒng)以某種方

54、式來(lái)處理這些信號(hào)即提取這些信號(hào)或提高這些信號(hào)的品質(zhì)，然后在適當(dāng)?shù)臅r(shí)間以適當(dāng)?shù)男问桨堰@個(gè)信號(hào)表示為輸出量。 illustrates the components in such a system. The central circles represent the two types of signal processing (digital and analog), while theblock between the two signal- processing blocks represents the conversion of an analog signal to equivalen

55、t digital form (A/D=Analog-to-Digital) and the reverse conversion of a digital signal to the corresponding analog form (D/A=Digital-to-Analog). The remaining blocks involve inputs and outputs getting signals into and out of the processing system. 圖2-2顯示了這樣一個(gè)系統(tǒng)的組成部分。中間的圓圈代表了兩種類型的信號(hào)處理（數(shù)字和模擬），而處于信號(hào)處理框之

56、間的方框表示模擬信號(hào)向等效數(shù)字形式（A/D即模擬到數(shù)字）的轉(zhuǎn)換，以及從數(shù)字信號(hào)向相應(yīng)的模擬形式（D/A即數(shù)字到模擬）的逆轉(zhuǎn)換。剩下的方框涉及輸入和輸出取得信號(hào)以及從處理系統(tǒng)輸出信號(hào)。Many electrical signals derived from physical systems are obtained from devices called transducers. We have already encountered an example of an analog transducer, the thermocouple pair. It converts temperatur

57、e difference (the physical variable) to a voltage (the electrical variable). Generally, a transducer is a device that converts a physical or mechanical variable to an equivalent voltage or current signal. Unlike the thermocouple example, however, most transducers require some form of electrical exci

58、tation to operate從物理系統(tǒng)獲得的很多電氣信號(hào)是從被稱為傳感器的器件中輸入的。我們已經(jīng)碰到了一個(gè)模擬傳感器的例子。即熱電偶。它把溫度的變化（物理變量）轉(zhuǎn)換成電壓（電氣變量）。通常，傳感器是一種將物理或機(jī)械變量轉(zhuǎn)換成等效電壓或電流信號(hào)的器件。然而，不同于熱電偶例子，大多數(shù)傳感器需要一些形式的電激勵(lì)以驅(qū)動(dòng)傳感器The output from a system can be in many forms, depending on the use to be made of the information contained in the input signals. One can

59、seek to display the information, either in analog form (using a meter, for example, in which the needle position indicates the size of the variable of interest) or in digital form (using a set of digital display elements that are lit up with a number corresponding to the variable of interest). Other possibilities are to convert the output to sound energy (with a loudspeaker), or to use the output asan input signal to a