exercise1
4. The Fourier series is a particular type of orthogonal series representation that is very useful in solving engineering problems, especial communication problems. The orthogonal functions that are used are either sinusoids, or, equivalently, complex exponential functions.
傅立叶级数是一种特殊类型的正交级数表示，它在解决工程问题，特别是通信问题时，十分有用。它所利用的正交函数是正弦函数或等价的复指数函数
5. For periodic waveforms, the Fourier series representations are valid over all time. Consequently, the (two-side) spectrum, which depends on the waveshape from t=–∞to t=∞, may be evaluated in terms of Fourier coefficients.
对于周期波形，傅立叶级数表示法在整个时间段都是有效的。因此，可以根据傅立叶系数，计算取决于t=–∞到t=∞之间波形的(双边)频谱。
4. It should be clear that the spectrum of a voltage (or current) waveform is obtained by a mathematical calculation and that it does not appear physically in an actual circuit. f is just a parameter (called frequency) that determines which point of the spectral function is to be evaluated.
应该清楚，电压（或电流）波形的频谱是通过数学计算获得的，并不从物理上出现于实际的电路中。f只是一个被称作频率的参数，它决定了要计算哪一点的频谱函数。
5. One of the particular interest is the consequence of working with real waveforms. In any physical circuit that can be built, the voltage (or current) waveforms are real functions (as opposed to complex functions) of time.
作用于实数（际？）波形的结果令人特别感兴趣。在可构建的物理电路中，电压或电流波形是关于时间的实函数（和复函数相对）。
work 起作用，造成
4. Pulse amplitude modulation (PAM) is an engineering term that is used to describe the conversion of the analog signal to a pulse-type signal where the amplitude of the pulse denotes the analog information.
脉冲幅度调制（PAM）是一个工程术语，用于描述从模拟信号到脉冲类型信号的转变。这里，脉冲幅度表示模拟信息。
5. If we assume that each of the digital words has n binary digits, there are M=2n unique code words that are possible, each code word corresponding to a certain amplitude level. However, each sample value from the analog signal can be any one of an infinite number of levels, so that the digital word that represents the amplitude closest to the actual sampled value is used. This is called quantizing.
如果假设每一个字有n个二进位，那么就可能有M=2n个不同的码字，每一个码字对应于一个特定的幅度大小。然而，来自模拟信号的每一个采样值，可能是无限多个数值中的任意一个。于是，用最接近于实际采样值幅度的字来表示，此过程称为量化。
code word 码字binary 二进位的digit 数字（0,1,2...）
4-3：The definition of a random process may be compared with that of a random variable. A random variable maps events into constants, whereas a random process maps events into functions of the parameter t.
译文：随机过程的定义可以和随机变量的定义相比较。随机变量把事件映射为常数，而随机过程则把事件映射为参数t的函数。
4-4：In summary, if a process is ergodic, all time and ensemble averages are interchangeable. The time average cannot be a function of time since the time parameter has been averaged out. Furthermore, the ergodic process must be stationary, since otherwise the ensemble averages (such as moments) would be a function of time. However, not all stationary processes are ergodic.
译文：总之，如果一个过程是各态历经的，那么所有的时间平均和总体平均是可互换的。时间平均不可能是时间的函数，因为时间参数已经被平均掉了。此外，各态历经过程一定是静态的，否则整体的平均（比如矩）将会是时间的函数。然而，并不是所有的静态过程都是各态历经的。
词汇：ergodic [????????] adj. [统]各态历经的；遍历的
平稳随机过程中任一随机样本函数的时间平均值与无限多个随机样本函数在同一时刻的平均值相等，即时间平均等于集合平均。如果被处理的随机信号是具有各态历经的平稳随机过程，它的样本函数集合平均可以用某一样本函数的时间平均来确定，这给随机信号的分析和处理带来很大方便。
ensemble [?????????●] n. 全体，整体
moment [统]矩；[物]力矩，转矩
5-1：当被测量不随时间变化或变化缓慢时，输出y与x之间的关系称为静态特性；当被测量随时间迅速变化时，输出y与x之间的关系称为动态特性。
When the measurand remains constant or changes slowly with time, the relationship between output y and x is referred to as static performance. When the measurand changes rapidly with time, the relationship between output y and x is referred to as dynamic performance.
约有18,300,000项符合"the relationship between"的查询结果
约有2,990,000项符合"the relationship of"的查询结果
5-3：A random error is due to a large number of independent small effects that cannot be identified or controlled, it is a statistical quantity. As such, it will vary for each replication of the observations. If a large number of readings is observed for the same quantity, the scatter of the data about a mean value can be evaluated. The scatter generally follows a gaussion distribution
about a mean value, which is assumed to be the true value.
(书上的“高斯”拼写错误。)
(不要将每0个“a/an”都译为“一个”)
译文：随机误差是由大量独立的微小的不可识别或控制的作用引起的，它是一个统计量。这样，对每次重复观测，它都将发生变化。如果对同一个量观测到了大量的读数，就可以算出数据关于平均值的散布。这种散布通常服从关于平均值的高斯分布，而平均值被假定为真值。
词汇：replication [ ???●????????] n. [统]重复(实验)；复制
gaussian [ ??◆????]adj.(德国数学家)高斯的
gauss [??◆?] n. 高斯
5-4：Accuracy is the deviation 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 is ±2 units for all readings.
译文：准确度是输出值与校准输入或真值之间的偏差。如前一节所述，假设一个伏特表的准确度是2%满刻度，则对所有读数的最大偏差是±2单位。
6-3：Uncertainty is generally stated as a number, indicating the tolerance from the true value of the measurand. The tolerance is only estimated. It represents the confidence level of the investigator in the results, since the true value of the measurement is unknown.
译文：不确定性通常用一个数来表述，它显示了距离被测量真值的公差。公差只能估计。它表示测量结果的置信度水平，因为测量的真值是未知的。
词汇：confidence [ ?????????] n. 置[可]信度；信心，信任
6-4：The（书上误为”he”）purpose of the sensor is to obtain dimensional information from the workpiece. It is like a transducer in many instances because it converts one energy form to another. This other energy form is always an electrical signal, since we are considering sensors which provide an electrical signal to be used as feedback to the process or machine control.
译文：检测元件的作用是获取工件的尺寸信息。和许多场合下的传感器一样，它把一种形式的能量转换为另一种形式。这另一种形式的能量总是电信号，因为我们正在考虑这样的传感器，它能提供电信号用于过程或机器控制的反馈。（which后的定语从句太长，可把它
另起一句，作为对先行词sensors的补充说明。）
词汇：
作“传感器”讲时，transducer和sensor有没有区别？
（1）传感器的英译名有transducer和sensor两个，一般常出现互用情况，如速度式流量传感器的英译名为velocity-type flow sensor；而插入式流量传感器的英译名则为insertion flow transducer。
（2）中华人民共和国行业标准——自控设计常用名词术语Common Terms and Definition for Measurement and Control System Design （HG/T 20699-2000）
检测元件，传感元件：sensor
（测量）传感器：(measuring ) transducer
7-3 Resolution and accuracy of the sensor are determined by the quality requirements of the part itself. Resolution is the smallest increment of distance that the sensor can resolve. In cases where the machine tool encoders are used to read location, the resolution may be determined by the encoders themselves.
词汇：
resolution [ ?????●?◆????] n. 分辨率；坚定，决心，解决
part 零件
resolve v. 分辨machine tool 机床encoder 编码器location n. 位置；存储单元译文：传感器的分辨率和准确度由零件本身的质量要求决定。分辨率是传感器所能分辨的最小距离增量。在使用机床编码器读取位置的情况下，分辨率可由编码器本身确定。
7-4 As discussed earlier, sensors can be broken down into four divisions: contact, noncontact, direction（direction 无形容词词性，所以怀疑应为direct）and indirect. No one sensor can be described as being the best overall, independent of application, since in-process sensing is heavily application dependent.
词汇：
division [????????] n [生物]类；分开，部门
independent of 不依赖...，独立于....
in process 在进行中
sense v. 检测，传感；感知，感觉
译文：如前面所讨论，传感器可分为四类：接触式、非接触式、直接式和间接式。不和应
用相结合，没有一种传感器是最优的，因为行进中的检测极大地取决于应用。
8-3：A simple air sensor consists of a regulated source of air, an adjustable restriction, and a nozzle with an orifice. With an object, the workpiece, blocking the nozzle, the pressure across the restriction is zero.
词汇：
regulate [ ????◆●???] vt. 管理，控制，调节
orifice [ ??????] n. 节流孔；孔，口
workpiece [ ????????] 工件
block vt. 阻塞，妨碍
译文：简单的空气传感器由调控气源、可调约束和带节流孔的喷嘴组成。如果物体或工件阻塞了喷嘴，则穿过约束的压力为零。
注：an 并不总是需要译成一个，注意英、汉的差异。
8-4：Available sensors have a variety of characteristics that must be understood before application. The major characteristics, physical size, resolution, accuracy, type of signal output, signal processing requirements, effective spot size are outlined herein.
词汇：
spot size 光斑尺寸；目标尺寸
spot n. 斑点，污点；场所vt. 弄脏
outline vt. 概述，描绘轮廓n. 大纲，轮廓，要点
herein adv. 于此, 在这里
译文：在使用之前，可用的传感器有许多特性需要了解。将物理尺寸、分辨率、准确度、输出信号的类型、信号处理要求、有效光斑尺寸等主要特性概述于此。
spot size：为了获得精确的温度读数，测温仪与测试目标之间的距离必须在合适的范围之内，所谓“光点尺寸”（spot size）就是测温仪测量点的面积。您距离目标越远，光点尺寸就越大。右图所示为距离与光点尺寸的比率，或称D：S。在激光瞄准器型测温仪上，激光点在目标中心的上方，有12mm（0.47英寸）的偏置距离。
测量距离与光点尺寸
在定测量距离时，应确保目标直径等于或大于受测的光点尺寸。
9-2 一只理想的安培表具有非常低的等效电阻，以致于它存在于任一电路时能使该电路的性质发生改变的程度尽可能小。
词汇：
安培表，电流计：amperometer (=ammeter[ ])
等效电阻：equivalent resistance
译文：The equivalent of resistance of an ideal amperometer is so low that its existence hardly changes the nature of the circuit.
注：整个句子采用so...that结构。
这个句子中文看起来有些生硬，象是从英文翻译过来的。
9-3 All electronic voltmeters use a dc meter movement for their readout. Consequently, the ac signal input must be converted from ac to dc before it can be displayed. The conversion must be such that the true rms value of the waveform is retained. There are a number of ways to do the conversion.
词汇：
DC：Direct Current 直流电
AC：Alternating Current交流电
RMS：Root Mean Square 均方根
译文：所有的电子电压表都采用直流表头作为读数器。因此，交流输入信号在被显示之前，必须转换为直流信号。这种转换必须保留波形的真实的均方根值。有多种方法可实现这种转换。
9-4 The equivalent resistance of a set of inter-connected resistors is the value of the single resistor that can be substituted for the entire set without affecting the current that flows in the rest of any circuit of which it is a part.
inter-：表示“在一起，交互”之义
译文：一组相联的电阻的等效电阻等于这样的单个电阻的值，它能够代替整组电阻而不影响流过它所在电路的其它任何部分的电流。
注：三重定句从句嵌套。最后一个it= a set of inter-connected resistors