测控技术与仪器专业英语课后阅读翻译

1、第1堂课后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.水下声波信号在声纳操作过程中，操作员经常需要对受噪声干扰的信号进行检波。干扰信号可能来自操 作员发出信号的反射波或者外部声源的信号。这两种类型的干扰对主动声纳和被动声纳都会造 成很大影响。类似的情况在击达监测、工程类和图像类专业的基本原理都会涉及到。当你想到信号检测时有多种方法，那么定义一个术语来表示特殊情况便是可行的。当问题 的答案是“当前有一

20、个还是一个多个信号？ ”时，检波一词将被使用。一个系统被设计来为这 种问题提供答案-无论是必然性还是偶然性，这就需要谈及假设检验；当一个信号反攵出现的情 况下，许多系统只被设计提供两个答案：“是的，当前有一个信号”或“不，当前没有信号” O 力图将信号分类会使问题复杂化，因为后者的结论将涉及到目标分类。一般来说，一种检波仪罂只被设计在固定的类型和参数下工作，不容易被改变，例如时间 积分检波电路和光学检测的辉光示波管。当出现不明信号时；观察者在拒绝或接收信号方面有 所迟疑。在这种情况下，操作员会有种感觉如果检波电路或者示波管能够延长时间那么他就能 下结论该信号是否存在。沃尔德（1950）在他的检

21、波理论系统阐述了这种直觉。如果（一个检 测检测方法）能够主动去改变时间间隔并在接收系统里储存数据以便达到确定的某水平，这 就是顺序检测。般不仅能够确定信号存在与否，而旦还能确定,个或多个与信号关联的参数。在还原完 整波形时我们所感兴趣的参数在各简单分量间有很大差别，例如信号的到达时间和相位。 当一个系统被设计来提取一个或多个信号参数时，这就是信号抽取。信号词并没有明确的定义，只是在读者对它有直观了解时的种假设。有些较为详细 的解称为了对信号词进定义可能导致是比较主观的或者狭隘与所应用的条件。也许你会说信 号就是你想观察到的而噪声就是对观察者产生干扰的信号。但是，个渔民在用声纳设备搜索 海洋时，

22、附近用来追踪潜艇的声纳干扰导致的信号削减常常会使他欣喜若狂。空不夸张地说， 一个人的信号将会是另一个人的喙声。信号的形式和构成是多种多样的。在主动声纳系统中，可以利用相关的固定宽度和调制 正弦信号。类似的有脉冲信号，例如爆炸或者撞击。在一些极端的情况可以利用伪随机信号。 在被动声纳系统中，例如螺旋桨或潜泳者发出的噪声。很明显，如何利用数学公式的方法来描 述一个信号成为了我们所面临的问题。即是在主动声纳系统中的超声波发射器传播已知波形的信号，但无法保证检测后杳找出来 的反射信号也是类似的波形。振幅和反向球面传播信号失去关联是检波系统最不利的情况，因 为它无法承担任何波形畸变。（偶然地，这种事件的

23、乐观情况并不适用于2维波，除非它传播到 足够远的地方，可以近似认为是平面波。）声波的传导介质会对其造成衰减，（衰减的程度）取 决于声波的频率。这就造成了少量的波形失真和对脉冲波形能谱造成相当的改变。主要的改变 还是由于波形的边缘效应和传播介质的不均匀所引起的。当反射波是由外部物体例如潜艇所发出的，这时反射波的结构主要受两种不同方式的影 响，第一，由两种反射信号之间的干扰导致外界声源的强度与跟随相位的改变迅速波动，第二, 合成反射波的延伸是沿着（来自）潜艇反射的散布特征，这就意味着持续时间取决于相位角的 简单特征。如果T是反射波由一个点扩散的持续时间，L是潜艇的K度，那么反射波的回射时 间就是，

24、是潜艇主轴和声纳拖戋线之间的夹角(锐角)，c则是声音在水中的传播速率。当然, 当接近的时候必须用潜艇的宽度代入。最后一个造成脉冲波形失真的原因声源，船体，介质，目标之间相对运动所造成的多普勒 效应。由于声源，介质，目标(或者被动接收的探测端)相对于船体都有不通的速度向量， 所以各种因素的影响之间的区别也很大。第五章课后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.个随机误差是由于控制,大辅的独立影响小,不能他发现或 这是个统计累。因此，它每个复制的观察。如果大信的读数是 同样数量的不同而不同。散射的数据他可以评估。散高斯分布通常遵循关于意味着value.

27、which被认为是真正的 价值,准确性是偏差的输出的输入或真正的校准价值。如果把电压表的准确性2%全面描述在前面的 部分最大偏差我,士 2units所有阅读资料。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.任何物体在任何温度高于绝对年度的辐射能最。这种辐射无论是在不同强度和在光漕分布和温度。因此。通过 测信温度可以推导出要么强度或频谱的辐射。总能最密度辎射从理想blackbody”(稍

32、后详细介绍)鉴于法律的Stefan-boltzmann E = 6 T E在是能量密度在W / cmz。6Stefan-boltzmarm的常数(5。6697 X 10 z W / cmz K)和T是绝对的温度(K),换句话说总辐射能最是成正比的第四绝对温度的力最。All对象。特别是理想黑体对象。也会吸收入射幅射.(Uiven时间致和他们隔绝放肆的加 热或冷却周围空气的影响或其他材料。他们最终会达到个临界戊他们吸收和辑射能量在相同的利率。()东北 的后果忠如果,个对象(,个温度传感器。例如)是种理想的黑体。走完全绝缘。和是在整个表面淹没与辐射 发射源。它最终将达到平衡来源和黑体校正源可用)，温

33、度传感器是个测景辐射的温度对象。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.红外辐射温度计可以创建的方式类似，在图1的辐射能量从热（或冷）对经都聚焦在个温度传感器。其温度然后 表明屈射强度落它。应该是小的传感器和低质量为合理的响应时间。热敏电阻提供高灵敏度低温度的测量而热 电偶提供必要的工作范围为高水平的辐射能成。在一些d

39、esigns. the传感器是隔绝外界条件下通过将它放置在我 空中。佞盛器的amplified. linearized输出。和美联储到输出指标或求音机。光学往往稍有不I可，图中所示。 在大多数应用程;洛 特别是在较低的温度下。大部分的福射将远红外线.这不是大多数眼镜了。这可能比使用 凹面镜反射来聚焦入射能量。而不是,个镜头。也许也是 个红色或会外过滤器在进口为了压制干扰由于流浪 环境光温度较高的使用可能需要减少总传入的能源使川灰色filter. shutter。或其他阻来Stefan-boltzmann 的法律。和适当的操作这些温度计。是假定辐射是来自一个完美的黑体的散热器。粗略的（和它不是我

40、们的 这里的怠感,没有反映出任何辎射可能落在它。所有入射能量被吸收。个non-blackbody对致反映外部幅射 也将反映出内部产生的辐射。降低辐射的能量在任何给定的温度.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(几:/几)C)(lidc I/J,)第6章课后习题.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.。不确定性是般表述数用表示宽容的过热 蒸气的真实价值。他宽容只是估计T。它代表了信心水平的调查员在结果中。自从的真正价值测量是未知的。他的目的是获取维度信息的传感器从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.它就像个传感器在许多情况下,因为它转换为个能源形式到另个。这其他能源形式总是个电信号。 因为我们正在考虑传感器提供个电信号作为反馈过程或机器的控制.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. 电涡流传感器在概念上是类似和性能的电容 传感器。它有,些差异 但可能更适合在些 应用程序.这两者之间最大的不同在于传感器操作的原则。 电涡流传感期利用电磁场的反对 电容式电场。这是使这noncontacting电能场 传感器不太敏感的影响高频交流也兴奋不已 源。由比产生的交变磁场散发的线阍生成艾迪 电流的近表面的材料被检查。这些电流。反过来。创建他们自己的微场。这夫妇线图。登加个电流 驱动电流.检测电流信号的解调电路。可以 校准中派生出的距离

48、是可能的因为这个领域的优势是个函数 距离从传感器到目标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.进步的模拟输出所需的这种类型的传感器是致的电容式传感器的。决议是有限的，由A / D转换器。size, range现货。 和靶距同电容装置中可用。个导电T件必须支持诱发的电流。关于现货大小。电涡流探测器方面的限制如此小的段 线圈。有足够的转向生成足够的磁场。可以伤口。自从 边缘领域影响输出。电涡流探头也仅限于constant-geometry这些错误的情况下可以确定和校准出来6 因为这个设备取决于涡流。这是一个近地表现农？ 其他变最所特有的,这种传感器,必须理

55、解“ 强度的感应磁场是个函数的状况材料.因为不同的材料有不同的电阻率。传感器必须 校准，为特定的材料。此外。其他材料等特点 孔隙率和密度影响输出结果。近地表条件包括等缺陷 裂缝或包裹体改变输出和可能与改变 距离被测量。事实上主要使用这种类型的传感器是表面的 和近地农材料缺陷。它是非常敏感的。Ultrasound 芦波可以利用测距获取维度信息。传感器的田皆包括发射机和接收机的声音的能景.在许多 情况下，发送器和接收器在同,个单元。距离信息被获取 通过测最交通所需时间回声返回。因为声音的速度 在中是已知的，距离可以自接从tofms决定 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