测控技术与仪器专业英语翻译 殷虹 河北工业大学适用

曲线的线性组合。

Fourier transform representation of discrete-time aperiodic signals

As we know, the Fourier series representation of a discrete-time periodic signal is a finite series, as opposed to the infinite series representation required for continuous-time periodic signals. There are corresponding differences between continuous-time and discrete-time Fourier transforms.

译为： 正如我们所知，离散时间周期信号的傅立叶级数表示为有限序列，与连续时间周期信号所要求的无限序列正好相反。在连续时间和离散时间的傅立叶变换式之间存在相应的区别。

Equations (5.9) and (5.10) are the discrete-time counterparts of eqs. (5.7) and (5.8). The function X(ejw) is referred to as the discrete-time Fourier transform and the pair of equations as the discrete-time Fourier transform pair. As in continuous time, the Fourier transform X(ejw) will often be referred to as the spectrum of x[n], because it provides us with the information on how x[n] is composed of complex exponentials at different frequencies.

译为：等式5.9和5.10为等式5.7和5.8的离散时间对。函数X(ejw) 被称为离散时间傅立叶变换且这一对等式被称为离散时间傅立叶变换对。正如在连续时间中一样，X(ejw) 的傅立叶变换常被成为x[n]的频谱，因为它提供给我们关于x[n]是如何由不同频率的复指数组成的相关信息

Unit 6 Signal Conditioning A measuring transmitter consists of two parts: a primary element (or sensor) and a signal conditioner. The primary element uses some characteristic of its material and construction to convert the value of a measured variable into an electrical, mechanical, or fluidic signal. 译为：一个测量传感器由两部分组成：一个基本元件（传感器）和一个信号调制器。基本元件利用其材质的特性和结构将被测量转化为电的、机械的或者流体的信号。 The output of the primary element may be a small voltage or an electrical resistance. It may be a force, a displacement, a pressure, or some other phenomenon. No matter what form it takes, the primary element output depends on the value of the measured variable.

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译为：基本元件的输出可能是一个小的电压或电阻。也可能是一个力、一个位移、一个压力或其他一些现象。不论它采取何种形式，基本元件的输出依赖于测得量的数值。

The output of the primary element is a measure of the variable it is sensing, but it is seldom in a form suitable for transmission and use by other components in a system.

译为：基本元件的输出是对它测量的变量的度量。但是它很少采用一种便于传输或被系统中其他部分使用的形式。

Usually, a signal conditioner is required to convert the primary element output into an electrical (or pneumatic) signal suitable for use by a controller or display device. A signal conditioner prepares a signal for use by another component. The input to a signal conditioner is usually the output from a sensor (or primary element). 译为：通常，一个信号调制器被用来将基本元件的输出变换为一个便于被处理器或显示设备使用的电（或气）信号。一个信号调节器将信号准备好以备其他设备使用，信号调制器的输入通常是传感器的输出（或基本元件）。 The full-scale outputs of most sensors (passive or active) are relatively small voltages, currents, resistances and capacitances. Before further analog or digital processing can take place, these outputs must be scaled or converted to useful ranges.

句中full-scale意为“满量程”，passive sensor意为“被动型传感器”，active sensor意为“主动型传感器”，scale在这里指“换算缩放，改变值的大小”。

译为：绝大多数传感器（被动型或主动型）的满量程输出都是比较小的电压、电流、电阻和电容。在进行进一步模拟或数字信号处理之前，这些输出必须要换算缩放或转换到可用的范围。

The standard transmission signals are a 4 to 20mA electric current or a 3 to 15psi pneumatic pressure. For example, a thermocouple（热电偶）(T/C) is a primary element that converts temperature into a small voltage.A signal conditioner converts the millivolt output of the thermocouple into a 4 to 20mA electric current. A T/C temperature transmitter includes both the thermocouple and the signal conditioner.

psi为压力的单位，pounds per square inch，磅/平方英寸。pneumatic pressure意为“气压”.

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译为：标准的传输信号是一个4至20毫安电流或一个一个3至15磅/平方英寸气压。例如，热电偶是一种将温度转化为小电压的基本元件。一个信号调制器将热电偶的毫伏输出转化为4至20毫安的电流，一个热电偶温度变送器同时包含热电偶和信号调制器。 Signal conditioning circuits perform the necessary amplification, level translation, impedance transformation, linearization and filtering. The characteristics of and error in the sensor output determine the type of signal conditioning circuits needed. 译为：信号处理电路实现必要的信号放大、电平变换、阻抗变换、线性化和滤波。信号调节回路执行需要的放大，转移电平，阻抗变换，线性化和滤波。传感器输出的特征及其误差决定需要哪种信号调制回路。

If the sensor output is not conditioned properly, factors such as sensitivity, voltage and current levels, linearity（线性度，线性）, impedances, gain, offset, drift, time constants, maximum electrical ratings（最大额定电功率）, stray impedances（杂散阻抗，寄生阻抗）and other important considerations can impact the overall performance of the sensor. As a result, the overall system will suffer, particularly when high resolution, precision or very low level measurements are involved.

译为：如果传感器的输出没有被正确的调制，诸如灵敏度、电压和电流电平、线性度、阻抗、增益、补偿、漂移、时间常数、最大额定电功率、寄生阻抗和其他重要的因素能够影响传感器的整体表现。其结果是整个系统将受到影响，特别是当涉及高清晰度，准确度或很差水平的测量时。

Care must be taken when designing signal generation and conditioning circuits to ensure that the sensor is the least accurate component of the system. If surrounding circuitry adds noise or degrades accuracy, the accuracy of the sensor output is compromised. 译为：设计信号发生器和调制回路时一定要警惕以保证传感器是系统中准确度最低的部件，如果周围回路有附加噪声或降低了准确度，传感器输出的准确度将受影响。 The following are some of the tasks performed by a signal conditioner: 以下是一个信号调制器执行的操作：

（1）Isolation and impedance conversion;隔离和阻抗变换

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（2）Amplification and analog-to-analog conversion; 放大和模-模转换

（3）Noise reduction (filtering); 降噪（滤波） （4）Linearization; 线性化 （5）Data sampling; 数据采样

（6）Digital-to-Analog conversion; 数-模转换 （7）Analog-to-Digital conversion. 模-数转换

Voltage output

Three types of input topologies exist for the signal conditioning of voltage output sensors: differential, single-ended and pseudo-differential. The type of signal conditioning input is typically matched to the output structure and precision requirements of the sensor . 句中differential有“微分”和“差分”之意，这里指信号处理的方式，意为“差动”。 译为：电压输出传感器的信号处理有3种输入拓扑方式：差动方式、单端方式和伪差分方式。信号调制输入的类型要符合特定的输出结构和传感器的准确性要求。

A differential device rejects input signals common to the balanced input pair (+ and -) while accepting the difference between the input signals, specified as the Common-Mode Rejection Ratio (CMRR). The device is designed so that the noise common to both inputs is rejected while the signal of interest is not.

句中balanced input意为“对称输入”，Common-Mode Rejection Ratio (CMRR)意为“共模抑制比”。

译为：差动装置在接收两输入端口的差分信号时，抑制这两个对称输入端口（+和-）的共模输入信号，这称为共模抑制比CMRR。这个装置被这样设计两个输入共有的噪声被抑制而所需要的信号不被抑制。

Much like digital differential input signals such as LVDS, the analog signals may be inverted to a double dynamic range as is common with differential output devices.

译为：和差分输入信号如低压差分信号很类似 ，模拟信号可以倒置成一个双重动态范围和差分输出设备的输出一样。

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This type of input topology（拓扑，拓扑结构，布局，拓扑学）is used when maximum noise rejection is required and the sensor measurement is not tied to ground, as with the Wheatstone bridge（惠斯顿电桥）configuration. For remote sensor applications, shielded twisted pair cables should be used in order to maintain signal balance and share a common ground reference.

句中twisted pair cables意为“双绞线”。

译为：这种输入拓扑形式在需要最大噪声抑制和传感器测量装置没有接地时使用，后者和惠斯顿电桥的结构相类似。对远程传感器应用，应该使用屏蔽双绞线以保持信号的平衡和共地。 In contrast, a single-ended (SE) device has a single signal input. The board designer must ensure a common ground between the device and its input, which is the sensor circuitry in this case. Therefore, SE devices are generally placed in close proximity to one another to mitigate（减轻，缓和）the possibility of reference differences between the devices. 译为：相反地，一个单端设备只有一个信号输入端。面板设计员必须保证设备和其输入之间有共同之处，传感器回路就是这种情况。因此，单端设备通常彼此紧密排列以减少设备间相互参照引起的不同的可能。

In general, SE devices are used for conditioning larger signals and are not tied directly to small signal sensors. Although SE devices have lower CMRRs and introduce greater DC offsets（偏移，偏置）, they are less costly. For remote sensor applications, coaxial（同轴的，共轴的）cables are sufficient for shielding the signal conductor and sharing common ground references.

译为：通常情况下，单端设备用来调制较大的信号而且不直接连接在小的信号传感器上。尽管单设设备有较低的共模抑制比和较大的直流抵消，它们更便宜，对长距离传感器设备而言，同轴电缆足够用于信号传导和共地。

Finally, a pseudo-differential input topology is a hybrid of the two. Its DC offset performance approaches that of a differential device, but its CMRR is closer to a SE device. This type of device is used in cost-sensitive designs with DC sensors where high frequency variations from noise can be removed at the end of the signal chain or through digital processing.

句中DC是direct current的缩写，意为“直流电”。

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测控专业英语翻译

Unit 1 Measurement, Control and Instrumentation

Instrumentation is defined as the art and science of measurement and control. Instrumentation engineers are responsible for controlling a whole system like a power plant. 译为：仪器可定义为测量和控制的艺术和科学。仪器工程师负责控制整个系统，比如一个电厂。

An instrument is a device that measures and/or regulates process variables such as flow, temperature, level, or pressure. Instruments include many varied contrivances that can be as simple as valves and transmitters, and as complex as analyzers. 译为：仪器是一种用来测量和/或调节过程变量（如流量、温度、液位或压力）的装置。仪器包括许多不同的设备，可以像阀和变送器那样简单，也可以像分析仪那样复杂。 Instruments often comprise control systems of varied processes such as refineries, factories, and vehicles. The control of processes is one of the main branches of applied instrumentation. Instrumentation can also refer to handheld devices that measure some desired variable. Diverse handheld instrumentation is common in laboratories, but can be found in the household as well. For example, a smoke detector is a common instrument found in most western homes. 译为：仪器通常由如精炼厂、工厂和车辆这些不同流程的控制系统组成。过程控制是实用仪器的主要分支之一。仪器也可以是测量某个所需变量的手持设备。多样化的手持式仪器常见于实验室，在日常生活中也可以发现。例如：烟雾探测器是西方家庭中的一种常见仪器。 Output instrumentation includes devices such as solenoids, valves, regulators, circuit breakers, and relays. These devices control a desired output variable, and provide either remote or automated control capabilities. These are often referred to as final control elements when controlled remotely or by a control system.

句中desired output variable意为“期望输出变量”，are referred to as意为“被称为”。 全句译为：输出仪器包括线圈、阀、调节器、断路器和继电器等元件。这些元件控制期望输出变量，使之实现远程或自动控制功能。在远程控制或自动控制系统中，称这些元件为

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终端控制元件。

Transmitters are devices that produce an output signal, often in the form of a 4～20mA electrical current signal, although many other options using voltage, frequency, pressure, or ethernet are possible. This signal can be used for informational purposes, or it can be sent to a PLC, DCS, SCADA system, LabView or other type of computerized controller, where it can be interpreted into readable values and used to control other devices and processes in the system.

译为：变送器是产生某种输出信号的装置，通常是 4—20mA的电流信号，当然也可以是电压、频率、压力或以太网。这个信号可作参考之用，还可以发送到PLC、DCS、SCADA系统、LabView或其它类型的计算机控制器，这个信号被转换成可读值，用于控制系统中的其它设备和过程。

Control Instrumentation plays a significant role in both gathering information from the field and changing the field parameters, and as such are a key part of control loops. 句中field意为“现场”，control loops意为“控制回路”。

全句译为：控制仪器在现场信息采集和现场参数转换中都起到了重要作用。这本身是控制回路的一个关键部分。

History

In the early years of process control, process indicators and control elements such as valves were monitored by an operator that walked around the unit adjusting the valves to obtain the desired temperatures, pressures, and flows. As technology evolved pneumatic controllers(气压式调节器) were invented and mounted（安装，配有）in the field that monitored the process and controlled the valves.

译为：在早年的过程控制中，过程指标和控制元件，如阀，是由操作员在装置周围走动通过调节阀门来监测，以获得所需的温度、压力和流量。随着技术的发展，气压式调节器发明了，并安装于监测过程和控制阀的现场。

This reduced the amount of time process operators were needed to monitor the process. Later years the actual controllers were moved to a central room and signals were sent into the control room to monitor the process and outputs signals were sent to the final control element such as a valve to adjust the process as needed.

译为：这样就减少了过程操作员监测过程所需的时间。近几年，实际控制转移到中央控

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制室，信号被发送到控制室来监测过程，并且输出信号被送到终端控制元件，如阀门，根据需要调节过程。

These controllers and indicators were mounted on a wall called a control board. 译为：这些控制器和指示器安装称为控制面板的壁面上。

The operators stood in front of this board walking back and forth monitoring the process indicators. This again reduced the number and amount of time process operators were needed to walk around the units. The basic air signal used during these years was 3～15 psig(磅/平方英寸).

译为：操作员在面板前面来回走动以监测过程指示器。这就再次减少了过程操作员在装置周围来回走动所需的时间。这几年使用的基本气压信号是3-15磅/平方英寸。 In the 1970s electronic instrumentation began to be manufactured by the instrument companies. Each instrument company came out with their own standard signal for their instrumentation, 10～50mA, 0.25～1.25V, 0～10V, 1～5V, and 4～20mA, causing only confusion until the 4～20mA was universally used as a standard electronic instrument signal for transmitters and valves.

译为：20世纪70年代仪器公司开始生产电子仪器。每个仪器公司为他们的仪器装置推出了自己的标准信号：如10~50mA, 0.25～1.25V, 0～10V, 1～5V, 和4～20mA，这只会引起混乱，直到4～20mA被普遍作为变送器和阀的标准电子仪器信号。

The transformation of instrumentation from mechanical pneumatic transmitters, controllers, and valves to electronic instruments reduced maintenance costs as electronic instruments were more dependable than mechanical instruments. This also increased efficiency and production due to their increase in accuracy. 句中reduced为transformation的谓语，as引导原因状语从句。

全句译为：从机械气动变送器、控制器和阀的控制方式向电子仪器控制方式的转变，降低了维修成本，因为电子仪器比机械仪器更可靠。同时由于精度的提高，从而提高了工作效率和产量。

The next evolution of instrumentation came with the production of Distributed Control Systems (DCS). The pneumatic and electronic control rooms allowed control from a

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centralized room, DCS systems allowed control from more than one room or control stations. These stations could be next to each other or miles away. Now a process operator could sit in front of a screen and monitor thousands of points throughout a large unit or complex.译为：伴随着分散式控制系统（DCS）的产生，仪器有了进一步的发展。气动控制和电气控制室允许来自一个集中室的控制，DCS系统允许来自多个控制台的控制。这些控制台可以是相邻的，也可以相隔千里。现在过程操作员可以坐在屏幕前监控整个装置和设备的成千上万的点。 Measurement

Instrumentation is usually used for measurement. Measurement is the process or the result of determining the magnitudes of many parameters (physical values). These parameters include:

（1）Chemical composition；化学成分 （2）Chemical properties； 化学性质 （3）Properties of light； 光的特性 （4）Vibration； 振动 （5）Weight； 重量 （6）Voltage 电压 （7）Inductance； 电感

译为：仪器通常用于测量。测量是确定一些参数（物理值）的大小的过程或结果。 （8）Capacitance； 电容 （9）Resistivity； 电阻 （10）Viscosity； 粘度

（11）Other mechanical properties of materials；材料的其它机械性能 （12）Properties of ionising radiation；电力辐射的性质 （13）Frequency； 频率 （14）Current； 电流

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（15）Pressure, either differential or static；压力（差压或静压） （16）Flow； 流量 （17）Temperature；温度 （18）Levels of liquids；液位等 （19）Density. 密度

With the exception of a few seemingly fundamental quantum constants, units of measurement are essentially arbitrary; in other words, people make them up and then agree to use them.

句中With the exception of意为“除……以外”，quantum constants意为“量子常数”。 全句译为：除了少数看上去代表基本法则的量子常数以外，测量的单位实质上是很主观的，换句话说，人们编制并愿意使用它就可以了。

Nothing inherent in nature dictates that an inch has to be a certain length, or that a mile is a better measure of distance than a kilometre. Over the course of human history, however, first for convenience and then for necessity, standards of measurement evolved so that communities would have certain common benchmarks（基准）. Laws regulating measurement were originally developed to prevent fraud （欺诈，欺骗行为；骗子） in commerce. 译为：本质上没有任何内在的事物决定：一英寸必须是某一特定的长度，或者一英里较一公里是一个较好的距离度量。然而，在人类历史的过程中，首先是为了方便起见，然后因为必要，测量标准逐渐形成了以便使社会有特定的共同基准。最初制定法律规范尺度就是为了防止商业欺诈。

Measurement methods are often scrutinized（仔细检查，详审） for their validity, applicability, and accuracy. It is very important that the scope of the measurement method be clearly defined, and any aspect included in the scope is shown to be accurate and repeatable through validation.

译为：通常要审核测量方法的有效性、适用性和准确性。明确界定测量方法的使用范围是非常重要的，并且这个范围里的任何方面通过验证被证明是正确的和可复验的。

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generating particular sequences of these patterns.

译为：又例如，考虑人的发声机制，这个机制通过对声学压力产生波动而产生语言。不同的声音对应声学压力变量的不同形式，并且人类的声音系统是通过产生这些变量形式的特定顺序而产生可理解的语言。

Signal are represented mathematically as functions of one or more independent variables. For example, a speech signal can be represented mathematically by acoustic pressure as a function of time, and a picture can be represented by brightness as a function of two spatial variables.

译为：信号用数学表示为包含一个或多个自变量的函数。例如，一个速度信号可以用数学表达为声压对时间的函数，一个图像可以表达为亮度对两个空间变量的函数。

In this context, we focus our attention on signals involving a single independent variable. For convenience, we will generally refer to the independent variable as time, although if may not in fact represent time in specific applications.

译为：在本文中，我们将注意力集中在包含单个自变量的信号上。为方便起见，我们通常将时间作为独立变量，尽管其实际上在特定应用中不一定表示时间。 For example, in geophysics(地球物理学), signals representing variations with depth of physical quantities such as density, porosity(孔隙率，多孔性), and electrical resistivity（电阻率）are used to study the structure of the earth. Also, knowledge of the variations of pressure, temperature and wind speed with altitude are extremely important in meteorological（与气象学有关的，气象的）investigations.

译为：例如，在地球物理学中，表示一些物理量如密度，有空性和电阻系数的深度的变化的信号被用来学习地球的结构。而且，随着高度变化的压力，温度和风速的信息在气象研究中极其重要。

Throughout this context, we will be considering two basic types of signals: continuous-time signals and discrete-time signals. In the case of continuous-time signals the independent variable is continuous, and thus these signals are defined for a continuum of values of the independent variable. On the other hand, discrete-time signals are defined only at discrete

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times, and consequently, for these signals, the independent variable takes on only a discrete set of values.

译为：贯穿整篇文章，我们将考察两种基本类型的信号：连续时间信号和离散时间信号。连续时间信号的自变量是连续的，因此这些信号定义为自变量的连续值。另一方面，离散时间信号只定义在离散时间点上，因此，对这些信号，自变量只在一系列离散的值上出现。 A speech signal as a function of time and atmospheric pressure as a function of altitude are examples of continuous-time signals. The weekly Dow-Jones stock market index is an example of a discrete-time signal.

译为：语音信号作为时间的函数和大气压作为高度的函数是连续时间信号的例子。每周的道琼斯股市指数是离散时间信号的例子

Other examples of discrete-time signals can be found on demographic （人口统计学的）studies in which various attributes, such as average budget, crime rate, or pounds of fish caught, are tabulated（把（数字、事实）列成表）against such discrete variable as family size, total population, or type of fishing vessel（渔船，渔轮）, respectively. 译为：其他离散时间信号的例子可以从人口分析学中找到，人口分析学的特征，例如人均财政预算，犯罪率，或者捕获鱼量各自与如家庭规模，总人口数或捕鱼船类型这样的离散变量列成表格。

To distinguish between continuous-time and discrete-time signals, we will use the symbol to denote the continuous-time independent variable and to denote the discrete-time independent variable. In addition, for continuous-time signals we will enclose the independent variable in parentheses (?), whereas for discrete-time signals we will use brackets [?] to enclose the independent variable. 句中parentheses特指“圆括号”。

全句译为：为了区分连续时间信号和离散时间信号，我们要使用特定符号表示连续时间自变量和离散时间自变量。另外，连续时间信号将自变量放在圆括号(·）中，而离散时间信号，我们用方括号[· ]来表示自变量。

We will also have frequent occasions when it will be useful to represent signals graphically. Illustrations of a continuous-time signal and discrete-time signal are shown in Figure 5.1. It is important to note that the discrete-time signal is defined only for integer values of the

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independent variable. Our choice of graphical representation for emphasizes this fact, and for further emphasis we will on occasion refer to as a discrete-time sequence. 译为：我们也经常会遇到当把信号用图表示出来更有效的情况，对连续时间信号和离散时间信号的说明如图5.1。离散时间信号中自变量只能用整数值来表示这一点很重要。我们选择用图形表示是为了强调这一点，并且为了进一步强调我们会在必要时提及离散时间序列。

Figure 5.1 Graphical representations of (a)continuous-time and (b) discrete-time signals

A discrete-time signal x[n] may represent a phenomenon for which the independent variable is inherently discrete. Signals such as demographic data are examples of this. On the other hand, a very important class of discrete-time signals arises from the sampling of continuous-time signals. In this case, the discrete-time signal x[n] represents successive samples of an underlying phenomenon for which the independent variable is continuous. 译为：一个离散时间信号x[n]也许代表一种现象其自变量本身就是离散的。人口统计学数据就是这种数据的例子.另一方面,一类很重要的离散时间信号来自对连续时间信号的采样。在这种情况下，离散时间信号x[n]代表一个其自变量是连续的现象的连续采样。 Because of their speed, computational power, and flexibility, modern digital processors are use to implement many practical systems, ranging from digital autopilots to digital audio system. Such systems require the use of discrete-time sequences representing sampled versions of continuous-time signals—e.g., aircraft position, velocity, and heading for an autopilot（自动导航装置，自动驾驶仪）or speech and music for an audio system. 译为：因为它们的速度,计算能力和适应性,现代数字处理器用来使许多实用的系统,从数字化自动驾驶仪到数字化组合音响得以实现。这样的系统要用离散时间序列来表达连续时间信号的样本描述。例如,飞机的空中姿态,速度和自动驾驶仪的导向或者组合音响的语音和音乐.

We can develop a representation of signals as linear combinations of a set of basic signals. For this alternative representation we use complex exponentials（复指数）. The resulting representations are known as the continuous-time and discrete-time Fourier series and transform. As we will see, these can be used to construct broad and useful classes of signals.

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译为：我们将信号描述为一组基本信号的线性组合。未使用这种变换表示我们使用复指数。最终的表达方式是连续时间和离散时间的傅里叶级数和傅里叶变换。正如我们所要看到的一样，这些表达方式可以用来构建大范围且有效用的一类信号。

In eq. (5.2), the term for k=0 is a constant. The terms for k = +1 and k = -1 both have components or the first harmonic components.

句中fundamental components意为“基波”，first harmonic components意为“一次谐波分量”。

全句译为：在式(5.2)中，k = 0项为常数，k = +1和k = -1两项都具有基频w0，称为基波或一次谐波分量。

The two terms for k = +2 and k = -2 are periodic with half the period (or, equivalently, twice the frequency) of the fundamental components and are referred to as the second harmonic components（二次谐波分量）. More generally, the components for k = +N and k = -N are referred to as the N th harmonic components （N次谐波分量）. 译为：K=+2和k=-2这两项的周期为周期的一半（或者等同于说其频率为基波频率的二倍）且被称为二次谐波分量。更一般的，k=+n和k=-n的成分被称为N次谐波分量。 As in continuous time, the discrete-time Fourier series coefficients ak are often referred to as the spectral coefficients of x[n]. These coefficients specify a decomposition of x[n] into a sum of N harmonically related complex exponentials. 句中spectral coefficients意为“频谱系数”。

全句译为：在连续时间中，离散时间傅里叶级数系数通常指x[n]的频谱系数。这些系数表示将x[t]分解成N个相关谐波复指数之和。

In either case, exactly the same set of complex exponential sequences appears in the summation on the right-hand side of eq. (5.5). As a consequence, the Fourier series representation of a discrete-time periodic signal is a finite series, as opposed to the infinite series representation required for continuous-time periodic signals.

译为：在任一例子中，特别是同一个复指数序列集合出现在等式5.5右边的和中，结果为 ,一个离散时间周期信号的傅立叶表达式为一个有限序列，与连续

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时间周期信号要求的无限序列表达式正好相反。

The development of Fourier transform representation for aperiodic signals in continuous time is one of Fourier’s most important contributions. Fourier reasoned that an aperiodic signal can be viewed as a periodic signal with an infinite period.

译为：在连续时间上的非周期信号的傅立叶变换表达式的发展史傅立叶最重要的贡献之一。傅立叶推理一个非周期信号可以看成一个周期为无穷大的周期信号。

Fourier transform representation of continuous-time aperiodic（非周期性的）signals More precisely, in the Fourier series representation of a periodic signal, as the period increases the fundamental frequency decreases and the harmonically related components become closer in frequency. As the period becomes infinite, the frequency components form a continuum and the Fourier series sum becomes an integral.

译为：更精确地讲，在对周期信号的傅里叶级数表达中，随着周期的增加，基频减小，谐波分量在频率上更加靠近。当频率变成无穷大，频率分量形成一个连续体，傅里叶级数求和变成一个积分。

Equations (5.7) and (5.8) are referred to as the Fourier transform pair(傅里叶变换对), with the function X(jw) referred to as the Fourier Transform or Fourier integral of x(t) and eq. (5.7) as the inverse Fourier transform(傅里叶反变换) equation. 译为：等式5.7和5.8被称为傅立叶变换对，函数X(jw) 成为傅立叶变换或x(t)的傅立叶级数。且式5.7成为傅立叶反变换等式。

In analogy （类似，相似，类推，类推法）with the terminology used for the Fourier series coefficients of a periodic signal, the transform X(jw) of an aperiodic signal x(t) is commonly referred to as the spectrum(频谱)of x(t), as it provides us with the information needed for describing x(t) as a linear combination (specifically, an integral) of sinusoidal（正弦曲线）signals at different frequencies.

译为：在类推用于周期信号的傅立叶变换的系数的专用术语中，X(jw)作为非周期信号x(t)的变形被称为x(t) 的频谱，因为它提供给我们信息，用来将x(t)表述为不同频率的正弦

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possible level and then to quantify the maximum remaining error that may exist in any instrument output reading. However, in many cases, there is a further complication that the final output from a measurement system is calculated by combining together two or more measurements of separate physical variables.

译为：在任何测量系统中，将误差减少到尽可能低的程度，然后量化可能存在于任何仪器输出读数中的最大误差，这是极其重要的。然而，在许多情况下，情况有点复杂，就是测量系统的最终输出是结合了两个或多个独立的测量物理变量而计算得到的。

In this case, special consideration must also be given to determining how the calculated error levels in each separate measurement should be combined together to give the best estimate of the most likely error magnitude in the calculated output quantity. 译为：在这种情况下，对于在每个单独的测量中，如何确定计算的误差等级，以及在计算输出量中给与尽可能最佳的误差幅度估计，还必须给予特殊的考虑。

The starting point in the quest(探求，寻找)to reduce the incidence of errors arising during the measurement process is to carry out a detailed analysis of all error sources in the system. Each of these error sources can then be considered in turn, looking for ways of eliminating or at least reducing the magnitude（量，量值，数量，尺度,大小，长度，重大，大量）of errors. Errors arising during the measurement process can be divided into two groups, known as systematic errors（系统误差）and random errors （随机误差）.

译为：寻求减少在测量过程中所产生的误差率的出发点是，在测量过程中对系统中的所有误差源进行详细分析。反过来考虑这些误差源中的每一个误差，就是寻找如何消除或至少减少误差的幅值。在测量过程中所产生的误差分为两组：系统误差和随机误差。 1．systematic errors 系统误差

Systematic errors describe errors in the output readings of a measurement system that are consistently on one side of the correct reading, i.e. either all the errors are positive or they are all negative. Two major sources of systematic errors are system disturbance during measurement and the effect of environmental changes (modifying inputs). 句中positive和negative分别指值的“正”、“负”。

全句译为：系统误差描述了测量系统中输出读数始终在正确读数一边的误差，即所有误差均

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为正或均为负。系统误差的两个主要来源是测量过程中的系统干扰和环境变化的影响（改变了输入）。

Other sources of systematic error include bent meter needles, the use of uncalibrated instruments, drift in instrument characteristics and poor cabling practices. Even when systematic errors due to the above factors have been reduced or eliminated, some errors remain that are inherent in the manufacture of an instrument. These are quantified by the accuracy figure quoted in the published specifications contained in the instrument data sheet.

译为：其他系统误差来源包括弯曲仪表指针，使用了未校准的仪器，仪器特性的漂移和糟糕的布线。即使已经减少或消除由于上述因素造成的系统误差，但是在制造仪器时仍然存在一些固有误差。这些误差在仪器数据表中所公布的规格，通过精确图引用而确定。 These various sources of systematic error, and ways in which the magnitude of the errors can be reduced, are discussed below. 译为：下面讨论这些不同的系统误差来源以及如何减小系统误差。 （1）System disturbance due to measurement 由测量引起的系统干扰

Thermometer（温度计）, which would initially be at room temperature, and plunge it into the water. In so doing, we would be introducing a relatively cold mass (the thermometer) into the hot water and a heat transfer would take place between the water and the thermometer. This heat transfer would lower the temperature of the water.

译为：将最初温度在室温下的温度计浸入水中。把一个相对寒冷的物质（温度计）放入热水中，然后在水和温度计之间就会有热量的传递。热量的传递会降低水的温度。

Whilst the reduction in temperature in this case would be so small as to be undetectable by the limited measurement resolution of such a thermometer, the effect is finite and clearly establishes the principle that, in nearly all measurement situations, the process of measurement disturbs the system and alters the values of the physical quantities being measured.

这是一个复杂长句。Whilst引导了让步状语从句。the effect是主语，后面跟了两个并列的谓语成分。that从句为the principle的同位语。

译为：虽然这种情况下温度的降低很小，以致这种温度计在有限的分辨率内无法测得，但这

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种有限的影响清楚地证实了这样一个原理：几乎所有的测量环境中，测量过程干扰了整个系统，改变了被测物理量的值。

Thus, as a general rule, the process of measurement always disturbs the system being measured. The magnitude of the disturbance varies from one measurement system to the next and is affected particularly by the type of instrument used for measurement. Ways of minimizing disturbance of measured systems is an important consideration in instrument design. However, an accurate understanding of the mechanisms of system disturbance is a prerequisite（先决条件，前提）for this.

译为：因此，一般来说，测量过程中总会干扰被测系统。扰动的大小因测量系统的不同而不同，并且特别容易受测量仪器类型的影响。如何使测量系统干扰的程度最小，是仪器设计时需要考虑的一个重要因素。当然，前提是需要准确地了解系统的干扰机制。 （2）Errors due to environmental inputs 环境输入引起的误差

An environmental input is defined as an apparently real input to a measurement system that is actually caused by a change in the environmental conditions surrounding the measurement system.

译为：环境输入的定义是，对于一个测量系统实际的真正输入是由测量系统周围的环境条件的变化引起的。

The static and dynamic characteristics specified for measuring instruments are only valid for particular environmental conditions (e.g. of temperature and pressure). static characteristic和dynamic characteristics指测量系统的“静态特性”和“动态特性”。 译为：测量仪器的静态特性和动态特性只在特定环境条件下有效（如温度和压力）。 These specified conditions must be reproduced as closely as possible during calibration exercises because, away from the specified calibration conditions, the characteristics of measuring instruments vary to some extent and cause measurement errors.

译为：在校准期间，这些特定条件必须尽可能准确的再现，因为当远离指定的校准条件时，测量仪器的特性在一定程度上发生变化，从而引起测量误差。

The magnitude of this environment-induced variation is quantified by the two constants known as sensitivity drift and zero drift, both of which are generally included in the

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published specifications for an instrument.

句中constants意为“常数”，sensitivity drift意为“灵敏度漂移”，zero drift意为“零点漂移”，简称“零漂”。

译为：环境导致的变化量由两个常数确定：灵敏度漂移和零点漂移。两者通常都在仪器的产品说明书中给出。

In any general measurement situation, it is very difficult to avoid environmental inputs, because it is either impractical or impossible to control the environmental conditions surrounding the measurement system. System designers are therefore charged with the task of either reducing the susceptibility of measuring instruments to environmental inputs or, alternatively, quantifying the effect of environmental inputs and correcting for them in the instrument output reading.

译为：在任何普通测量环境下，是很难避免环境输入的影响，因为控制测量系统周围的环境条件是不切实际的，或许也是不可能的。因此，系统设计师要么承担降低测量仪器对环境输入的敏感性的任务，要么在仪器输出读数时量化环境输入的影响，并进行纠正。 （3）Wear（磨损，损耗）in instrument components 仪表元件的磨损 Systematic errors can frequently develop over a period of time because of wear in instrument components. Recalibration often provides a full solution to this problem. 译为：经过一段时间，因为仪表部件的磨损，可能频繁产生系统误差。重新校准仪器经常提供解决这个问题的完整方案。 （4）Connecting leads （引线，引线脚）

In connecting together the components of a measurement system, a common source of error is the failure to take proper account of the resistance of connecting leads (or pipes in the case of pneumatically or hydraulically actuated measurement systems). 句中take proper account of意为“考虑”，connecting leads意为“连接线”。

译为：在测试系统各部件的连接中，常见的误差源是没有恰当考虑连接线（或气压、液压驱动测试系统的管线）的电阻。

For instance, in typical applications of a resistance thermometer, it is common to find that

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the thermometer is separated from other parts of the measurement system by perhaps 100 metres. The resistance of such a length of 20 gauge （直径，口径，码，厚度，规格） copper wire is 7 , and there is a further complication that such wire has a temperature coefficient （系数）of 1m /℃. Therefore, careful consideration needs to be given to the choice of connecting leads.

译为：例如，在电阻温度计的典型应用中，常常可以能发现温度计和其他的测量系统部分分开至少100米。长度为20的铜线的电阻是7，更复杂的说这种导线的温度系数是1M / ℃。因此，连接导线的选择需要认真考虑。

Not only should they be of adequate cross-section so that their resistance is minimized, but they should be adequately screened if they are thought likely to be subject to electrical or magnetic fields that could otherwise cause induced noise. 此句注意应在正确理解核心意思后再译，全句可简练译为：（连接线）不仅要有足够的横截面使电阻降到最小，而且在考虑到电磁干扰时要恰当屏蔽。

The prerequisite for the reduction of systematic errors is a complete analysis of the measurement system that identifies all sources of error. Simple faults within a system, such as bent meter needles and poor cabling practices, can usually be readily and cheaply rectified once they have been identified. However, other error sources require more detailed analysis and treatment. Various approaches to error reduction are considered below. 译为：减少系统误差的前提条件是对测量系统进行完整的分析，确定所有不同来源的误差。在一个系统内的简单故障，如弯曲的仪器指针和糟糕的布线，一旦它们被确定，通常可以很容易而又粗略的进行纠正。然而，对于其他误差来源，需要更详细的分析和处理。以下将介绍不同的减小误差的方法。

（1）Careful instrument design 细心的仪器设计

Careful instrument design is the most useful weapon in the battle against environmental inputs, by reducing the sensitivity of an instrument to environmental inputs to as low a level as possible.

译为：细心的仪器设计是减小环境输入误差的最有用的武器，这种方法是将仪器对环境输入的灵敏度降低到尽可能低的水平。

（2）Method of opposing inputs 反向输入方法

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The method of opposing inputs compensates for the effect of an environmental input in a measurement system by introducing an equal and opposite environmental input that cancels it out.

反向输入方法，通过引入一个大小相等，方向相反的环境输入，来抵消测量系统中的环境输入的影响。

（3）High-gain feedback 高增益反馈

Highgain feedback techniques are often a very effective way of reducing a measurement system’s sensitivity to environmental inputs. However, one potential problem that must be mentioned is that there is a possibility that high-gain feedback will cause instability in the system. Therefore, any application of this method must include careful stability analysis of the system.

译为：高增益反馈技术，是一个降低测量系统对环境输入敏感性的非常有效的方法。然而，必须提到一个潜在的问题，即有一种可能性，就是高增益反馈会引起系统不稳定。因此，应用此方法必须对系统进行仔细的稳定性分析。 （4）Calibration 校准

Instrument calibration is a very important consideration in measurement systems. All instruments suffer drift in their characteristics, and the rate at which this happens depends on many factors, such as the environmental conditions in which instruments are used and the frequency of their use. Thus, errors due to instruments being out of calibration can usually be rectified by increasing the frequency of recalibration. 译为：仪器校准是测量系统中的一个非常重要的考虑因素。所有仪器都有漂移的特性，而发生这种情况的频率取决于许多因素，如环境条件，使用何种工具及其频率。因此，仪器超出标定范围产生的误差通常可以通过增加再标定的频次来修正。 （5）Manual correction of output reading 输出读数的手动校正

In the case of errors that are due either to system disturbance during the act of measurement or due to environmental changes, a good measurement technician can substantially reduce errors at the output of a measurement system by calculating the effect of such systematic errors and making appropriate correction to the instrument readings. 译为：对于由测量过程中的系统干扰或者环境变化引起的误差，一个好的测量技术人员

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可以通过计算系统误差的影响和适当的修正仪表读数来减小误差。

This is not necessarily an easy task, and requires all disturbances in the measurement system to be quantified. This procedure is carried out automatically by intelligent instruments. 译为：这并非易事，需要量化测量系统中的所有干扰。智能仪表可以自动的实施该过程。

（6）Intelligent instruments 智能仪表

Intelligent instruments contain extra sensors that measure the value of environmental inputs and automatically compensate the value of the output reading. They have the ability to deal very effectively with systematic errors in measurement systems, and errors can be attenuated to very low levels in many cases.

译为：智能仪表包含了额外的传感器来测量环境输入，并进行自动补偿然后输出读数。他们有能力而又有效的处理测量系统的系统误差，在许多情况下误差可以被降低到非常低的程度。

2. Random errors 随机误差

Random errors are perturbations of the measurement either side of the true value caused by random and unpredictable effects, such that positive errors and negative errors occur in approximately equal numbers for a series of measurements made of the same quantity.

译为：随机误差是由随机和未知的影响引起的位于真值两边的测量的扰动量，对同一测量量的测量序列，正误差和负误差的值大约相等。

Such perturbations are mainly small, but large perturbations occur from time to time, again unpredictably. Random errors often arise when measurements are taken by human observation of an analogue meter, especially where this involves interpolation（篡改；添写；插补）between scale points. Electrical noise can also be a source of random errors. 译为：这种扰动很小，但有时会发生大的扰动，而这又是不可预知的。当由人观察模拟仪表进行测量时，随机误差会经常发生，尤其是在涉及到数值范围点之间的插值情况时。电气噪声也是随机误差的来源之一。

To a large extent, random errors can be overcome by taking the same measurement a number of times and extracting a value by averaging or other statistical techniques. However,

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any quantification of the measurement value and statement of error bounds remains a statistical quantity.

译为：在很大程度上，随机误差可以通过在相同的多次测量条件，以及对通过提取平均值或其他统计技术来克服。然而，任何测量值的定量和误差范围的声明仍然是一个统计量。 Because of the nature of random errors and the fact that large perturbations in the measured quantity occur from time to time, the best that we can do is to express measurements in probabilistic terms: we may be able to assign a 95% or even 99% confidence level that the measurement is a certain value within error bounds of, say, ±1%, but we can never attach a 100% probability to measurement values that are subject to random errors.

句中from time to time意为“有时，偶尔”，confidence level意为“置信水平”。全句译为：鉴于随机误差的性质和测量值有时会有巨大的波动，表达测量结果最好的方法是概率论：我们可以令置信概率为95%甚至99%，则测量值具有±1%的误差界，但由于随机误差的存在，测量值永远不能达到100%的置信概率。 Statistical characteristics of measurements subject to random errors mainly include mean and median values, Standard deviation and variance, etc. 译为:易受随机误差的影响的测量统计特征主要包括：平均值和中值，标准偏差和方差等。 （1）Mean and median values 平均值和中值

The average value of a set of measurements of a constant quantity can be expressed as either the mean value or the median value. As the number of measurements increases, the difference between the mean value and median values becomes very small.

译为:一系列恒定量测量的平均值可表示为平均值或中值。随着测量次数的增加，平均值和中值之间的差距会变得越来越小。

This is valid for all data sets where the measurement errors are distributed equally about the zero error value, i.e. where the positive errors are balanced in quantity and magnitude by the negative errors.

译为：对于所有的数据集，它们的测量误差均匀的分布在0值附近，这是有效的。即正误差在数量和幅度上能够与负误差平衡。

（2）Standard deviation and variance 标准差和方差

Expressing the spread of measurements simply as the range between the largest and smallest value is not in fact a very good way of examining how the measurement values are

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distributed about the mean value. A much better way of expressing the distribution is to calculate the variance or standard deviation of the measurements.

译为：表示测量的传播，简单地说就是在最大值和最小值之间的范围内，研究测量值的平均值是如何分布的，这其实不是一个很好的方法。一个表达分布的更好方式是计算测量的方差或标准差。

译为：计算这些参数的起点是从平均值计算每次测量的偏差（误差） di The standard deviation （ ） is simply the square root of the variance. Thus: 译为：标准差（ ）仅仅是方差的平方根。因此有：

We have observed so far that random errors can be reduced by taking the average (mean or median) of a number of measurements. However, although the mean or median value is close to the true value, it would only become exactly equal to the true value if we could average an infinite number of measurements. As we can only make a finite number of measurements in a practical situation, the average value will still have some error. This error can be quantified as the standard error of the mean.（标准平均误差，平均值的标准差） 译为：到目前为止，已经注意到，通过测量平均（均值或中值）以减小随机误差。然而，尽管平均值或中值接近真值，如果我们采取无限数量的测量，才会等于真值。在实际情况下，进行的测量次数是有限的，所以采用平均值法仍会有误差存在。这个误差可以由平均值的标准误差确定。

Finally, a word must be said about the distinction between systematic and random errors. Error sources in the measurement system must be examined carefully to determine what type of error is present, systematic or random, and to apply the appropriate treatment. In the case of manual data measurements, a human observer may make a different observation at each attempt, but it is often reasonable to assume that the errors are random and that the mean of these readings is likely to be close to the correct value.

译为：最后，还必须指出关于系统误差和随机误差之间的区别。在测量系统中，必须仔细检查误差来源，以确定是哪种类型的误差，是系统误差还是随机误差，以便应用适当处理措施。在人工数据测量时，观察人员可能每次有不同的观察，但是常常一个合理的假设是：假定那些误差是随机的，并且读数的平均值也是接近真值的。

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However, this is only true as long as the human observer is not introducing a parallax(视差)-induced systematic error as well by persistently reading the position of a needle against the scale of an analogue meter from one side rather than from directly above. In that case, correction would have to be made for this systematic error (bias) in the measurements before statistical techniques were applied to reduce the effect of random errors.

译为：但是，只有观察者不引进视觉性的系统误差，并坚持从一个模拟仪表的侧面位置而不是上方读取刻度位置，那么上述的假定就是合理的。在那种情况下，在使用统计技术以减少随机误差的影响之前，必须先校正测量中的系统误差（偏差）。

Unit5 Signal Description Signal may describe a wide variety of physical phenomena. A signal is any physical variable whose magnitude or variation with time contains information. This information might involve speech and music, as in radio broadcasting, a physical quantity such as the temperature of the air in the room, or numerical data, such as the record of stock market transactions.

译为：信号可以描述许多自然现象。一个信号可以是任意的物理变量，其随时间的大小和变化包含着信息。这个信息可能包含语言和音乐，例如无线电信号，一个物理量如房间内的温度，或数值化数据，如股市交易记录。

Although signal can be represented in many ways, in all cases the information in a signal is contained in a pattern of variation of some form. For example, the variations over time of the applied force f and the resulting automobile velocity v are signals.

译为：尽管信号可以用多种方式进行描述，在所有情况下一个信号中的信息总是包含在一定形式中的变量中。举例来说，随时间变化的外力f的变量和其产生的汽车速度是信号。

As another example, consider the human vocal (有声的，发音的)mechanism, which produces speech by creating fluctuations(波动，涨落，起伏) on acoustic (声音的，听觉的)pressure. Different sounds correspond to different patterns in the variations of acoustic pressure, and the human vocal system produces intelligible (可理解的，明白易懂的，清楚的) speech by

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