測控技術(shù)與儀器專業(yè)英語課后閱讀翻譯

1、第1堂課后Underwater Acoustic SignalIn the operation of a sonar system the operator is repeatedly faced with the problem of detecting a signal which is obscured by noise. This signal may be an echo resulting from a transmitted signal over which the operator has some control, or it may have its origin in

2、some external source. These two m(xles of operation arise in radar surveillance and in disciplines for techniques and for illustrations of the basic principles.Since there are many ways in which one can think about signal detection , it is desirable to define a term to denote special cases . The wor

3、d detection will be used when the question to be answered is, Arc one or more signals present?5 when the system is designed to provide an answered to this question , either deterministic or probabilistic, one speaks of hypothesis testing. The case of a single signal occurs so often that many system

4、are designed to provide only two answers, Yes , a signal is present, or No, there is no signal/ One can make the problem more complicated by endeavoring to classif)- the signal into categories. Decisions of this latter kind will be referred to as target classification.Normally a piece of detection e

5、quipment is designed to operate in a fixed mode and the parameters such as integrating time of rectifier circuits or persistence of the oscilloscope tube for visual detection cannot be changed readily. There will always be some uncertain signals, which the observer will be hesitant to reject or acce

6、pt. In these cases the operator might have the feeling that if the integrating time of the detector or the persistence of the oscilloscope tube were longer, he could reach a decision about the existence of the signal. Wald( 1950) has formulated this intuitive feeling into a theory of detection. When

7、 one is able to vary deliberately the interval over which one stores data in (he reception system in order to achieve a certain level of certainty, one speaks of sequential detection. Frequently it is desirable to determine not only the presence or absence of the signal but also one or more paramete

8、rs associated with the signal. The parameters of interest can vary widely from a simple quantity such as time of arrival or target bearing to the recovery of the complete waveform . When a system is designed to recover one or more parameters associated with the signal, one speaks of signal extractio

9、n.The word signal was not defined and it was assumed that the reader had an intuitive felling for the word. Some elaboration may be in order since the definition of signal subjective and depends on the application . One may say that signal is what one wants to observe and noise is anything that obsc

10、ures the observation. Thus, a tuna fisherman who is searching the ocean with the aid of sonar equipment will be overjoyed with sounds that arc impairing the performance of a nearby sonar system engaged in tracking a submarine. Quite literally, one mans signal is another mans noise.Signals come in al

11、l shapes and forms. In active sonar system one may use simple sinusoidal signals of fixed duration and modulations thereof. There are impulsive signals such as those made with explosions or thumpers. At the other extreme one may make use of pseudorandom signals. In passive systems, the signals whose

12、 detection is sought may be noise in the conventional meaning of the word; noise produced by propellers or underwater swimmers, for example. It should be evident that one of our problem will be the formulation of mathematical techniques that can be used to describe the signal. Although the source in

13、 an active sonar search system may be designed to transmit a signal known shape, there is no guarantee that the return signal whose detection is sought will be similar. In fact, there are many factors to change the signal. The amplitude loss associated with inverse spherical spreading is most unfort

14、unate for the detection system nut it does not entail any distortion of the wave shape . (Incidentally, where the wave can be approximated locally as a plane wave.) The acoustic medium has an attenuation factor , which depends on the frequency . This produces a slight distortion of the wave shape an

15、d a corresponding change in the energy spectrum of the pulse. The major changes in the waveform result from acoustic boundaries and inhomogeneities in the medium.When echoes are produced by extended targets such as submarines, there are two distinct ways in which echo structure is aflected. First, t

16、here is the interference be:ween reflections from the different leads to a target strength that fluctuates rapidly with changes in the aspect. Secondly, there is theelongation of the composite echo due to the distribution of reflecting features along the submarines. This means that the duration of t

17、he composite echo is dependent in a simple manner on the aspect angle. If T is the duration of the echo from a point scatterer, and L is the length of the submarine, the duration of the returned echo will be T=（2L/c）cosA,where A is the acute angle between the major axis of the submarine and the line

18、 joining the source and the submarine. C is the velocity of sound in the water. Of course, LcosA must be replaced by the beam width of the submarine when A is near. A final source of pulse distortion is the Doppler shifts produced by the relative motions between the source, and the target （or detect

19、or in passive listening） may each have a different velocity relative to the bottom, the variety of effects may be quite large.水下聲波信號在聲納操作過程中，操作員經(jīng)常需要對受噪聲干擾的信號進(jìn)行檢波。干擾信號可能來自操 作員發(fā)出信號的反射波或者外部聲源的信號。這兩種類型的干擾對主動聲納和被動聲納都會造 成很大影響。類似的情況在擊達(dá)監(jiān)測、工程類和圖像類專業(yè)的基本原理都會涉及到。當(dāng)你想到信號檢測時有多種方法，那么定義一個術(shù)語來表示特殊情況便是可行的。當(dāng)問題 的答案是“當(dāng)前有一

20、個還是一個多個信號？ ”時，檢波一詞將被使用。一個系統(tǒng)被設(shè)計來為這 種問題提供答案-無論是必然性還是偶然性，這就需要談及假設(shè)檢驗；當(dāng)一個信號反攵出現(xiàn)的情 況下，許多系統(tǒng)只被設(shè)計提供兩個答案：“是的，當(dāng)前有一個信號”或“不，當(dāng)前沒有信號” O 力圖將信號分類會使問題復(fù)雜化，因為后者的結(jié)論將涉及到目標(biāo)分類。一般來說，一種檢波儀罌只被設(shè)計在固定的類型和參數(shù)下工作，不容易被改變，例如時間 積分檢波電路和光學(xué)檢測的輝光示波管。當(dāng)出現(xiàn)不明信號時；觀察者在拒絕或接收信號方面有 所遲疑。在這種情況下，操作員會有種感覺如果檢波電路或者示波管能夠延長時間那么他就能 下結(jié)論該信號是否存在。沃爾德（1950）在他的檢

21、波理論系統(tǒng)闡述了這種直覺。如果（一個檢 測檢測方法）能夠主動去改變時間間隔并在接收系統(tǒng)里儲存數(shù)據(jù)以便達(dá)到確定的某水平，這 就是順序檢測。般不僅能夠確定信號存在與否，而旦還能確定,個或多個與信號關(guān)聯(lián)的參數(shù)。在還原完 整波形時我們所感興趣的參數(shù)在各簡單分量間有很大差別，例如信號的到達(dá)時間和相位。 當(dāng)一個系統(tǒng)被設(shè)計來提取一個或多個信號參數(shù)時，這就是信號抽取。信號詞并沒有明確的定義，只是在讀者對它有直觀了解時的種假設(shè)。有些較為詳細(xì) 的解稱為了對信號詞進(jìn)定義可能導(dǎo)致是比較主觀的或者狹隘與所應(yīng)用的條件。也許你會說信 號就是你想觀察到的而噪聲就是對觀察者產(chǎn)生干擾的信號。但是，個漁民在用聲納設(shè)備搜索 海洋時，

22、附近用來追蹤潛艇的聲納干擾導(dǎo)致的信號削減常常會使他欣喜若狂。空不夸張地說， 一個人的信號將會是另一個人的喙聲。信號的形式和構(gòu)成是多種多樣的。在主動聲納系統(tǒng)中，可以利用相關(guān)的固定寬度和調(diào)制 正弦信號。類似的有脈沖信號，例如爆炸或者撞擊。在一些極端的情況可以利用偽隨機(jī)信號。 在被動聲納系統(tǒng)中，例如螺旋槳或潛泳者發(fā)出的噪聲。很明顯，如何利用數(shù)學(xué)公式的方法來描 述一個信號成為了我們所面臨的問題。即是在主動聲納系統(tǒng)中的超聲波發(fā)射器傳播已知波形的信號，但無法保證檢測后杳找出來 的反射信號也是類似的波形。振幅和反向球面?zhèn)鞑バ盘柺リP(guān)聯(lián)是檢波系統(tǒng)最不利的情況，因 為它無法承擔(dān)任何波形畸變。（偶然地，這種事件的

23、樂觀情況并不適用于2維波，除非它傳播到 足夠遠(yuǎn)的地方，可以近似認(rèn)為是平面波。）聲波的傳導(dǎo)介質(zhì)會對其造成衰減，（衰減的程度）取 決于聲波的頻率。這就造成了少量的波形失真和對脈沖波形能譜造成相當(dāng)?shù)母淖?。主要的改?還是由于波形的邊緣效應(yīng)和傳播介質(zhì)的不均勻所引起的。當(dāng)反射波是由外部物體例如潛艇所發(fā)出的，這時反射波的結(jié)構(gòu)主要受兩種不同方式的影 響，第一，由兩種反射信號之間的干擾導(dǎo)致外界聲源的強(qiáng)度與跟隨相位的改變迅速波動，第二, 合成反射波的延伸是沿著（來自）潛艇反射的散布特征，這就意味著持續(xù)時間取決于相位角的 簡單特征。如果T是反射波由一個點(diǎn)擴(kuò)散的持續(xù)時間，L是潛艇的K度，那么反射波的回射時 間就是，

24、是潛艇主軸和聲納拖戔線之間的夾角(銳角)，c則是聲音在水中的傳播速率。當(dāng)然, 當(dāng)接近的時候必須用潛艇的寬度代入。最后一個造成脈沖波形失真的原因聲源，船體，介質(zhì)，目標(biāo)之間相對運(yùn)動所造成的多普勒 效應(yīng)。由于聲源，介質(zhì)，目標(biāo)(或者被動接收的探測端)相對于船體都有不通的速度向量， 所以各種因素的影響之間的區(qū)別也很大。第五章課后A random erroris due to acontrolled,large number of independent small effects that cannothe identified orit is a statistical quantity. As su

25、ch, iteach replication of the observations. If a large number of readings is will vary for the same quantity.the scatter of the data about a mean value can be evaluated.The scatter generally follows a guassian distribution about a mean value.which is assumed to be the true value.Accuracy is the devi

26、ation of the output from the calibration input or the true value. If the accuracy of a voltmeter is 2% full scale as described in the preceding section the maximum deviation i、士 2units fbr all readings.個隨機(jī)誤差是由于控制,大輔的獨(dú)立影響小,不能他發(fā)現(xiàn)或 這是個統(tǒng)計累。因此，它每個復(fù)制的觀察。如果大信的讀數(shù)是 同樣數(shù)量的不同而不同。散射的數(shù)據(jù)他可以評估。散高斯分布通常遵循關(guān)于意味著value.

27、which被認(rèn)為是真正的 價值,準(zhǔn)確性是偏差的輸出的輸入或真正的校準(zhǔn)價值。如果把電壓表的準(zhǔn)確性2%全面描述在前面的 部分最大偏差我,士 2units所有閱讀資料。第五章.Noncontact Temperature MeasurementAny object at any temperature above absolute zero radiates energy. This radiationvaries both in intensity and in spectral distribution with temperature. Hence.temperature may be ded

28、uced by measuring either the intensity or the spectrum of theradiation.The total energy density radiating from an idcarblackbodymorc on that later) isgiven by the Stefan-boltzmann law E=6T-where E is energy density in W/cmz.6 Isthe Stefan-boltzmann constant(5. 6697 X 10 rz W/cmz K)and T is the absol

29、utctcmpcrature(K).In other words the total radiated energy is proportional to the fburthpower of the absolute temperature.All objects.particularly ideal blackbxiy objects.also absorb incident radiation.(Uiven time to equilibrate.and presuming they are insulated from the heating or cooling effects of

30、 surrounding air or other materials.they will eventually reach a point where they absorb and radiate energy at equal rates. ()ne consequence of this is that if an object (a temperature sensor.for example) is an ideal blackbody.is perfectly insulated.and is flooded on its entire surface with radiatio

31、n from a radiating source.it will eventually reach an equilibrium sources and blackbody calibration sources are available).thc temperature of the sensor is a measure of the temperature of the radiating object.任何物體在任何溫度高于絕對年度的輻射能最。這種輻射無論是在不同強(qiáng)度和在光漕分布和溫度。因此。通過 測信溫度可以推導(dǎo)出要么強(qiáng)度或頻譜的輻射?？偰茏蠲芏容w射從理想blackbody”(稍

32、后詳細(xì)介紹)鑒于法律的Stefan-boltzmann E = 6 T E在是能量密度在W / cmz。6Stefan-boltzmarm的常數(shù)(5。6697 X 10 z W / cmz K)和T是絕對的溫度(K),換句話說總輻射能最是成正比的第四絕對溫度的力最。All對象。特別是理想黑體對象。也會吸收入射幅射.(Uiven時間致和他們隔絕放肆的加 熱或冷卻周圍空氣的影響或其他材料。他們最終會達(dá)到個臨界戊他們吸收和輯射能量在相同的利率。()東北 的后果忠如果,個對象(,個溫度傳感器。例如)是種理想的黑體。走完全絕緣。和是在整個表面淹沒與輻射 發(fā)射源。它最終將達(dá)到平衡來源和黑體校正源可用)，溫

33、度傳感器是個測景輻射的溫度對象。An infrared radiation thermometer may be created in a manner similar to that inFigure 1 the radiated energy from the hot(or cold) object is focused on a temperature sensor, whose temperature then is indicative of the intensity of the radiation falling uponit. The sensor should be sma

34、ll and low mass for reasonable response time. Thermistorsoffer high sensitivity for low temperature measurements while thermocouples providethe operating range necessary for high levels of radiated energy. In some dcsigns.thesensor is insulated from ambient conditions by placing it in a vacuum. The

35、sensofs output is amplified.linearized.and fed to an output indicator or recorder.The optics are apttobe abit different than shown in diagram.Inmostapplications.particularlyatlowertemperatures.muchof theradiation willbefarinfrared.which is not passed well by most glasses. It may be preferable to use

36、 areflective concave mirror to focus the incoming energy.rather than a lens. There mayalso be a red or infrared filter over the inlet to keep down interference due to strayambient light. For higher temperature use it may be necessary to reduce the totalincoming energy using a gray filter.shutter.or

37、other obstruction. The Stefan-boltzmann law.and the proper operation of thesethermometers.presumes that theradiation is coming from a perfect blackbody* radiator, to oversimplify（and it is not ourintention here to which does not reflect any radiation which may fall upon it. Allincidcnt energy is abs

38、orbed. A non-blackbody object which reflects external radiation will also reflect internally generated radiation.lowering the amount of energy radiated atany given temperature.紅外輻射溫度計可以創(chuàng)建的方式類似，在圖1的輻射能量從熱（或冷）對經(jīng)都聚焦在個溫度傳感器。其溫度然后 表明屈射強(qiáng)度落它。應(yīng)該是小的傳感器和低質(zhì)量為合理的響應(yīng)時間。熱敏電阻提供高靈敏度低溫度的測量而熱 電偶提供必要的工作范圍為高水平的輻射能成。在一些d

39、esigns. the傳感器是隔絕外界條件下通過將它放置在我 空中。佞盛器的amplified. linearized輸出。和美聯(lián)儲到輸出指標(biāo)或求音機(jī)。光學(xué)往往稍有不I可，圖中所示。 在大多數(shù)應(yīng)用程;洛 特別是在較低的溫度下。大部分的福射將遠(yuǎn)紅外線.這不是大多數(shù)眼鏡了。這可能比使用 凹面鏡反射來聚焦入射能量。而不是,個鏡頭。也許也是 個紅色或會外過濾器在進(jìn)口為了壓制干擾由于流浪 環(huán)境光溫度較高的使用可能需要減少總傳入的能源使川灰色filter. shutter?；蚱渌鑱鞸tefan-boltzmann 的法律。和適當(dāng)?shù)牟僮鬟@些溫度計。是假定輻射是來自一個完美的黑體的散熱器。粗略的（和它不是我

40、們的 這里的怠感,沒有反映出任何輜射可能落在它。所有入射能量被吸收。個non-blackbody對致反映外部幅射 也將反映出內(nèi)部產(chǎn)生的輻射。降低輻射的能量在任何給定的溫度.Any surface has a reflectivity and an emissivity. Reflectivity, r, is simply the ratioof reflected energy to incident energy:a perfect reflector has a reflectivity of onc;ablackbo y/巨 expCC=/J=T)- y大一大Which may be

41、simplified to =(consl)R exp 大一大wherecn77s/(T)7 了 sC(幾:/幾)C)(lidc I/J,)第6章課后習(xí)題.Uncertainty is generally stated as a number indicating the tolerance from the true value of the measunind. T he tolerance is only estimated. It represents theconfidcnce level of the investigator in the results.since the tr

42、ue value of themeasurement is unknown, he purpose of the sensor is to obtain dimensional information from theworkpiece.。不確定性是般表述數(shù)用表示寬容的過熱 蒸氣的真實價值。他寬容只是估計T。它代表了信心水平的調(diào)查員在結(jié)果中。自從的真正價值測量是未知的。他的目的是獲取維度信息的傳感器從theworkpieceo. It is like a transducer in many instances because it converts oneenergy form to ano

43、ther. This other energy form is always an electrical signal.since we are considering sensors which provide an electrical signal to be used asfeedback to the process or machine control.它就像個傳感器在許多情況下,因為它轉(zhuǎn)換為個能源形式到另個。這其他能源形式總是個電信號。 因為我們正在考慮傳感器提供個電信號作為反饋過程或機(jī)器的控制.第六章 Eddy Current(Readihg Material)The eddy

44、 current sensor is similar in concept and perfonnance to the capacitive sensor. It does have some differences though that may make it more suitable in some applications. The major difference between the two sensors is the principle of operation.The eddy current sensor utilizes an electromagnetic fie

45、ld as opposed to the capacitive electric field. It is the electromagnetic field that makes this noncontacling sensor much less sensitive to the effect of excited by a high-frequency alternating-current source. The resultant alternating magnetic field emanating from the coil generates eddy currents i

46、n the near surface of the material being inspected. These currents.in turn, create their own magnetic field.which couples to the coiLsuperimposing a current on the driving current. Demodulating circuitry detects this current signal.which can be calibrated to derive a distance is possible since the f

47、ield strengths are a function of the distance from the sensor to the target. 電渦流傳感器在概念上是類似和性能的電容 傳感器。它有,些差異 但可能更適合在些 應(yīng)用程序.這兩者之間最大的不同在于傳感器操作的原則。 電渦流傳感期利用電磁場的反對 電容式電場。這是使這noncontacting電能場 傳感器不太敏感的影響高頻交流也興奮不已 源。由比產(chǎn)生的交變磁場散發(fā)的線閽生成艾迪 電流的近表面的材料被檢查。這些電流。反過來。創(chuàng)建他們自己的微場。這夫婦線圖。登加個電流 驅(qū)動電流.檢測電流信號的解調(diào)電路?？梢?校準(zhǔn)中派生出的距離

48、是可能的因為這個領(lǐng)域的優(yōu)勢是個函數(shù) 距離從傳感器到目標(biāo)Progressing required fbr the analog output of this type of sensor is identical to that for the capacitive sensor. Resolution is limited by the A/D converter. Spot size.range, and standoff distance are comparable to those available in a capacitive device. A conductive work

49、piece is required to support the induced currents. Concerning spot size.the eddy current probe has limitations in terms of how small a coil.with enough turns to generate a sufficient magnetic field.can be wound. Since fringe fields have an effect on the output.the eddy current probe is also limited

50、to constant-geometry situations where these errors can be determined and calibrated out.Since this device depends on eddy currents.which are a near-surface phenomenon thcre are other variables peculiar to this sensor that must understood.The strength of the induced magnetic field is a function of th

51、e condition of the material. Because different materials have different resistivities.the sensor must be calibrated for a specific material. In addition.other material characteristics such as porosity and density affect the output. Near-surface conditions including defects such as cracks or inclusio

52、ns alter the output and may be indistinguishable from changes in the distance being measured. Indeed.the primary use of this type of sensor is for surface and near-surface material defects.to which it is very sensitive. Ultrasound Sound waves can be utilize by ranging to obtain dimensional informati

53、on. The configuration of the sensor involves a transmitter of sound energy and receiver. In many cases the transmitter and receiver are in the same unit. Distance information is obtained by measuring the transit time required for the echo the return. Since the speed of sound in the medium is known,

54、distance can be determined directly from time-of-flight information.進(jìn)步的模擬輸出所需的這種類型的傳感器是致的電容式傳感器的。決議是有限的，由A / D轉(zhuǎn)換器。size, range現(xiàn)貨。 和靶距同電容裝置中可用。個導(dǎo)電T件必須支持誘發(fā)的電流。關(guān)于現(xiàn)貨大小。電渦流探測器方面的限制如此小的段 線圈。有足夠的轉(zhuǎn)向生成足夠的磁場。可以傷口。自從 邊緣領(lǐng)域影響輸出。電渦流探頭也僅限于constant-geometry這些錯誤的情況下可以確定和校準(zhǔn)出來6 因為這個設(shè)備取決于渦流。這是一個近地表現(xiàn)農(nóng)？ 其他變最所特有的,這種傳感器,必須理

55、解“ 強(qiáng)度的感應(yīng)磁場是個函數(shù)的狀況材料.因為不同的材料有不同的電阻率。傳感器必須 校準(zhǔn)，為特定的材料。此外。其他材料等特點(diǎn) 孔隙率和密度影響輸出結(jié)果。近地表條件包括等缺陷 裂縫或包裹體改變輸出和可能與改變 距離被測量。事實上主要使用這種類型的傳感器是表面的 和近地農(nóng)材料缺陷。它是非常敏感的。Ultrasound 蘆波可以利用測距獲取維度信息。傳感器的田皆包括發(fā)射機(jī)和接收機(jī)的聲音的能景.在許多 情況下，發(fā)送器和接收器在同,個單元。距離信息被獲取 通過測最交通所需時間回聲返回。因為聲音的速度 在中是已知的，距離可以自接從tofms決定 信息。Ultrasonic energy.which is b

56、eyond the audible frequency range.is normally utilized since the wavelength of audible sound energy is relatively long compared with the resolution required for most dimensional measurements. For higl:- resolution applications.with measurement resolutions finer than 0. 1 in., a liquid couplant (typi

57、cally water) is required because the sound energy at the higher frequencies is highly attenuated in air. In an inprocess measurement application.water-or oil-based cutting fluids can serve as a coupling medium. The workpiece under measurement need not be immersed as a continuous stream of liquid can

58、 adequately convey the sound. The transmitter/receiver for an ultrasonic sensor is typicallyThe crystal itself is mechanically damped in order to attenuate a piezoelectric crystal.oscillation and avoidmasking the weak incoming echoes. The pulser is a fast.higl: voltage switch that drives the transdu

59、cer with a short rise time pulse that is converted into a mechanical pressure wave. The longitudinal sound wave is conveyed by the medium to the target.where it is reflected back to the transducer The same crystal or an identical one converts the echo to an electrical impulse.which is amplified by a

60、 tunedA timer is generally triggered by the pulse unit amplifier.and disabled by receipt of theincoming echo. The value held by the timer is the time of flight of the sound wave.that is.the time it takes the sound is constant for homogenous materials at a fixed temperature.the distance to the target