电气专业英语课文翻译

电气专业英语课文翻译
电气专业英语课文翻译

An electric circuit (or network) is an interconnection of physical electrical device. The purpose of electric circuits is to distribute and convert energy into some other forms. Accordingly, the basic circuit components are an energy source (or sources), an energy converter (or converters) and conductors connecting them.

电路(或者网络)是物理电气设备的一种互相连接。电路的目的是为了将能量分配和转换到另外一种形式中。因此,基本的电路元件包括电源、电能转换器以及连接它们的导体。

An energy source (a primary or secondary cell, a generator and the like) converts chemical, mechanical, thermal or some other forms of energy into electric energy. An energy converter, also called load (such as a lamp, heating appliance or electric motor), converts electric energy into light, heat, mechanical work and so on.

电源(原生电池或者再生电池、发电机等类似装备)将化学能量、机械能量,热能或者其他形式的能量转换成电能。电能转换器(也称为负载,如灯泡、电热器或者电动机)将电能转换成光、热、机械运动等等。Events in a circuit can be defined in terms of e.m.f. (or voltage) and current. When electric energy is generated, transmitted and converted under conditions such that the currents and voltages involved remain constant with time, one usually speaks of direct-current (D.C.) circuits.

电路属性可以根据电动势和电流来定义。当电能在产生、传输和变换时,若电路中相关的电流和电压不随时间而变化,我们便称其为直流电路

With time-invariant currents and voltages, the magnetic and electric fields of the associated electric plant are also time-invariant. This is the reason why no e.m.f.s of self-(or mutual-)induction appear in D.C. circuits, nor are there any displacement currents in the dielectric surrounding the conductors.

在电流和电压时不变的情况下,相关电气设备的电磁场也是时不变的。这就是为什么直流电路中没有自(互)感电动势、以及围绕在导体附近的电介质没有位移电流。

Fig.1.1 shows in simplified form a hypothetical circuit with a storage battery as the source and a lamp as the load. The terminals of the source and load are interconnected by conductors (generally but not always wires).

图1.1给出了一个假设电路的简单形式:一个蓄电池作为电源、以及一个灯泡作为负载。电源和负载的终端用导体互相连接,通常这种导体是导线,但少数情况下也有例外。

As is seen, the source, load and conductors form a closed conducting path. The e.m.f. of the source causes a continuous and unidirectional current to circulate round this closed path.

如图所示,电源、负载和导体构成了一个闭合导电回路。电源的电动势产生一个连续的单方向电流在闭合回路中流通。

The simple circuit made up of a source, a load and two wires is seldom, if ever, met with in practice. Practical circuits may contain a large number of sources and loads interconnected in a variety of ways.

这种由一个电源、一个负载和两根导线组成的简单电路在实践中即使有时能遇到,也是很少见的。实际的电路包括很多用不同方法连接起来的电源和负载。

To simplify analysis of actual circuits, it is usual to show them symbolically in a diagram called a circuit diagram, which is in fact a fictitious or, rather, idealized model of an actual circuit of network. Such a diagram consists of interconnected symbols called circuit elements or circuit parameters.

为了简化分析,通常用电路图来象征性地表示实际的电路。实际上,电路图是实际电路的一个假设模型,或相当于一个理想模型。这样的电路图包括电路元件或者电路参数等互联符号。

Two elements are necessary to represent processes in a D.C. circuit. These are a source of e.m.f. E and of internal (or ―source‖) resistance RS, and the load resistance (whic h includes the resistance of the conductors) R (Fig.1.2).

在直流电路中,有两个元件是有必要描绘出来处理的。这就是电源的电动势E、内阻RS,以及负载电阻R (其中包含了导体电阻)。

Whatever its origin (thermal, contact, etc.), the source e.m.f. E(Fig.1.2(a)) is numerically equal to the potential difference between terminals 1 and 2 with the external circuit open, that is, when there is no current flowing through the source.

无论图1.2(a)中的电动势E的原动力是什么(即不论是热的、机械的还是其它什么形式),其大小就等于1、2两端之间的开路电压,也就是电源没有电流通过的情况。

The source e.m.f. is directed from the terminal at a lower potential to that at a higher one. On diagram, this is shown by arrows.

电动势从较低电压端指向较高电压端,这在图表中用箭头表示。

When a load is connected to the source terminals (the circuit is then said to be loaded) and the circuit is closed, a current begins to flow round it. Now the voltage between source terminals 1 and 2 (called the terminal voltage) is not equal to its e.m.f. because of the voltage drop VS inside the source, that across the source resistance RS .

当一个负载加在电源两端(也就是说电路被加上负载),同时电路闭合,就有电流开始流通。这时在电源1、2两端之间的电压(称为端电压)不等同于电源的电动势,因为这时电源内阻RS两端将产生电压降VS。Fig.1.3 shows a typical so-called external characteristic of a loaded source (hence another name is the load characteristic of a source). As is seen, increase of current from zero to I~I1 causes the terminal voltage of the source to decrease linearly

图1.3表示带负载电源的一个典型的外特性(由于电源带负载,所以也称为电源的负载特性)。如图所示,当电流从0增加到I1时,引起电源端电压的线性减小。

In other words, the voltage drop VS across the source resistance rises in proportion to the current. This goes on until a certain limit is reached. Then as the current keeps rising, the proportionality between its value and the voltage drop across the source is upset, and the external characteristic ceases to be linear.

This decrease in voltage may be caused by a reduction in the source voltage, by an increase in the internal resistance, or both. The power delivered by a source is given by the equality PS=EI, where PS is the power of the source.

电源1、2两端电压的减小可能是由于电源电压的减小或电源内阻的增加引起的,也可能是两种情况共同引起的。电源提供的功率由等式PS=EI表示,其中PS是电源的功率。

It seems relevant at this point to dispel a common misconception about power. Thus one may hear that power is generated, delivered, consumed, transmitted, lost, etc. In point of fact, however, it is energy that can be generated, delivered, consumed, transmitted or lost.

这个公式恰当地消除了对功率的一个普遍的误解。例如有人可能听过功率被产生、释放、消耗、传输、损耗等等。然而,实际上是能量才能够被产生、释放、消耗、传输或损耗。

Power is just the rate of energy input or conversion, that is, the quantity of energy generated, delivered, transmitted etc per unit time. So, it would be more correct to use the term energy instead of power in the above context. Yet, we would rather fall in with the tradition.

功率只是能量输入或者转换的比率,也就是说,单位时间内产生能量、释放能量、传输能量的数量。因此,在上文中用能量这个术语代替功率会更准确些。但是,我们一般采用传统的说法。

The load resistance R(Fig.1.2(b)), as a generalized circuit element, gives an idea about the consumption of energy, that is, the conversion of electric energy into heat, and is defined as P=I2R.In the general case, the load resistance depends solely on the current through the load, which in fact is symbolized by the function R(I).

负载电阻R作为一个普遍的电路元件,给出了能量消耗的概念,也就是电能转化成热能,定义为P=I2R。一般情况下,负载电阻只由流过负载的电流决定,用方程R(I)表示。

By Ohm‘s law, the voltage across a resistance is V=RI.In circuit analysis, use is often made of the reciprocal of the resistance, termed the conductance, which is defined as g=1/R.

从欧姆定律可知,电阻两端的电压表示为V=RI。在电路分析中,经常使用电阻的倒数,称为电导,定义为g=1/R.

In practical problems, one often specifies the voltage across a resistance as a function of current V(I),or the inverse relation I(V) have come to be known as volt-ampere characteristics.

在实际问题中,通常规定横跨电阻的电压为关于电流的方程V(I),或者是反比关系I(V),这就是众所周知的伏安特性。

Fig.1.4 shows volt-ampere curves for a metal-filament lamp V1(I), and for a carbon-filament lamp V2(I). As is seen, the relation between the voltage and the current in each lamp is other than linear (nonlinear). The resistance of the metal-filament lamp increases (with increase of current), and that of the carbon-filament lamp decreases with increase of current.

图1.4给出了金属丝灯泡和碳丝灯泡的伏安曲线。如图所示,每个灯泡的电压和电流关系并不是线性的,当电流升高时,金属丝灯泡的电阻增大,碳丝灯泡的内阻减小。

Electric circuits containing components with non-linear characteristic are called non-linear.

If the e.m.f and internal resistances of sources and associated load resistances are assumed to be independent of the current and voltage, respectively, the external characteristic V(I) of the sources and the volt-ampere characteristic V1(I) of the loads will be linear(Fig.1.5).

包含非线性特性元件的电路称为非线性电路。如果假定电源的电动势和内阻以及相连的负载电阻分别与电流和电压无关,那么电源的外特性V(I)和负载的伏安特性V1(I)将是线性的(如图1.5所示)。

Electric circuits containing only elements with linear characteristic are called linear.Most practical circuits may be classed as linear. Therefore, a study into the properties and analysis of linear circuits is of both theoretical and applied interest.

只包含具有线性特性的元件的电路称为线性电路。很多应用电路都归类为线性电路,因此,对线性电路的特性和分析的学习具有理论和实际应用的双重意义。

An operational amplifier may be treated as a single electronic component with input and output terminals, rather as transistor is. The amplifier itself consists of a number of transistor stages such as those described in other lesson, fabricated and interconnected on a single substrate, and the user has access to a limited number of terminal points. Thus, of most interest from the applications point of view are the terminal characteristics.

运算放大器可以看做一个具有输入端口和输出端口的单个电子元件,就像晶体管那样。放大其本身由多级晶体管组成,这样的多极晶体管在前述课程中已经介绍,他们制作和连接在一块基板上,有几个引出端可供客户使用。从使用的角度看,人们感兴趣的是端口特性。

The name operational amplifier came about from the use to which early versions of the amplifiers were put, which was to provide electronic analogs of mathematical operations such as addition, Subtraction, Multiplication, Integration etc. Present-day usage is very much wider scope but the popular name ―op-amp‖ persists.

运算放大器这个名字起源于早期放大器的用途,他被用来进行一些电子模拟数学运算,例如,加减乘积分等,如今它的使用范围已大大扩展,但运算放大器这个通用名字却流传下来。

The operational voltage amplifier is represented schematically by the triangular symbol. A0 is the voltage gain from differential input to single-ended output and is always a positive number. Phase reversals are taken into account at the input terminals, which is the reason why these are labeled + and -. The voltage at each terminal, including the output, may be referred to common reference, usually ground, and unless otherwise stated, this common reference will be assumed. Thus,letting V(+) represent the voltage of the positive input terminal, we may define the differential input voltage as Vid=V(+)-V(-), and the output voltage is V0=A0Vid. If, however, the differential input voltage is defined as Vid=V(-)-V(+), the output voltage is V0=-A0Vid.

电压运算放大器可用三角形符号来表示。A0表示从差动输入端到单一输出端的电压增益,并恒为正值,考虑到在输入端可能会有反向输入的情况,所以要标上+号与-号。每个端口包括输出端口的电压,都可以选一个共同的参考点,通常选大地。除非另有说明,否则所假定的参考点就是地。这样用V+代表正相输入端对参考点的电压,而V—则代表负相输入点对参考点的电压,我们可以将差动电压定义为Vid=V(+)+V(-),输出电压V0=A0Vid。然而,如果差动输入电压定为Vid=V(-)-V(+);则输出电压V0=-A0Vid。

Because no phase reversal takes place in the circuit, the positive input terminal is termed the noninverting terminal, and because a phase reversal dose take place in the circuit, the negative input terminal is termed the inverting terminal. These terminals will always be specified in the manufacturer‘s data sheet for an amplifier. One or other of the input terminals may be connected to the common line, and the phase relationships still hold as shown. Note that the inverting terminal convention does not mean that the positive input must be connected to the noninverting and the negative input to the inverting; the amplifier may be used either way up, so to speak.

因为当信号从正输入端输入时电路不发生反相,所以称之为同相端,而从负输入端输入时,电路发生反相,因此称之为反相端。这些端口在放大器的铭牌上已注明。输入端口的一端或其他的端都可连到参考点,可以看出其他相位关系仍保持不变。注意,称反相端和同相端的惯例,并不意味着正信号输入一定要与同相端相连,而负信号输入一定要与反相端相连,可以说放大器可以采取其中任何一种使用方式。

The basic equivalent circuit for the operational voltage amplifier is shown in fig. Ri is the differential input resistance, and will always be high, usually in the megohm range. High input resistance may be achieved through the use of Darlington connected pairs in the input stage , or by using an FET differential input pair, as described in other lesson. R0 is the output resistance, and always be low, usually less then 100, for the operational voltage amplifier. A0 is the voltage gain as defined in the previous section, and this will always be large, of the order of 10^6:1. For many applications, the amplifier may be represented by an voltage amplifier, for which ……

电压放大器的基本等值电路如图所示。Ri为差动输入电阻,切总是很大,经常在兆欧级范围内。高输入电阻可以通过在输入端使用达林顿连接对来实现,或如前所述,通过使用一个FET差动输入对来实现。R0为输出电阻,并且总是很小。对电压运算放大器来说,通常不到100欧。A0为前几节所定义的电压放大倍数,他总是很大。大约属于10^6:1的数量级。在许多实际应用中,放大器可用一理想放大器来代表,这时:The concept of infinite voltage gain, or , for that matter, a very high but finite voltage gain, requires some explanation,. A voltage gain of 10^6:1 does not mean that a one-volt input signal would be amplified up to one million volts at the out put! In fact, the maximum out put voltage is limited by the bias supply voltage, typically ±15V. Howeve r, an input signal of one microvolt will be amplified up to one volt at the output, and, because the amplifier is always used in circuits in which a large fraction of the output voltage is fed back to the input, the differential input voltage may be assumed negligible in comparison with the feedback component, or in other words, Vid is assumed zero. This gives rise to the odd situation in which a zero input voltage, multiplied by an infinite voltage gain, results in a finite and very ordinary level output. The technique for analyzing this situation is illustrated in the next section.

对无穷大电压增益(此处即指非常大却有限的电压增益的概念)在此需要一些解释。10^6:1的电压增益并不代表将1V的电压输入信号放大成10^6V的输出信号,实际上最大输出信号电压由偏置电源电压所限制,典型值为正负15V。然而,一个微伏级输入信号在输出端将放大到1V,同时因为放大器一般用于输出电压有一大部分反馈到输入端的电路中,所以差动输入电压与反馈部分比可忽略不计,或者换句话说,Vid假定为0。这样就产生一个奇特的现象,输入电压为0,乘以一个无穷大的电压增益,得到一个有限的常规输出电压,这种情况的分析技巧将在下一节中阐述。

The basic inverting amplifier circuit is shown in fig, in which ideal operational voltage amplifier is assumed. The input voltage Vi is fed to the inverting terminal through a resistor R1, and the noninverting terminal is connected to ground (or the common reference line). Feedback from output to input occurs through resistor R2. Now, because Vid=0 for the ideal amplifier, the inverting terminal is at the same potential as the noninverting terminal, and is termed a virtual ground. Because of the virtual ground, the input loop voltage equation may be written as Vid=i1R1. For the same reason, the output voltage loop equation may be written as V0=i2R2. Because Ri is assumed infinite, the input current ii is zero, and, therefore i1=-i2. Collecting and rearranging gives for the terminal voltage gain:……基本反向放大器的电路如图所示,其中假设了一个理想的电压运算放大器,输入电压Vi通过一电阻R1输到反相端,并且同相端直接接地(或者接到公共参考线上)。输出端到输入端的反馈电压出现在电阻R2上。因为对理想放大器来说,Vid=0,因此其反相端与同相端电势相等,并称为虚地。因为是虚地,输入回路电压方程便可写成……同样输出电压方程可写成。。。因为已经令r1无限大输入电流为0,所以整理后得端口电压增益

The significance of this result is that the terminal voltage gain, which is the usable voltage gain, is independent of the parameters of the amplifier, and depends only on the external components R1 and R2. Had A0 been assumed large but finite, the terminal gain would be reduced approximately by a factor(1-1/A0), and it can be seen that with A0 of the order of 10^6:1 this factor is very close to unity. It is also assumed in the ideal amplifier that the output resistance is zero so that zero voltage drop results, internal to the amplifier. A0is known as the open loop gain because it is the voltage gain which would result with the feedback loop open; the results of feedback with amplifiers of finite A0 are described in other lesson.

这个结论的意义在于端电压增益(这是很有用的电压增益)与放大器的参数无关,而只取决于外部元件R1和R2.若A0真的假定为很大但有限,端口电压增益就会大致下降一个系数(1-1/A0)。可以看出,由于A0属于10^6:1数量级,因此这个系数非常接近于1.在理想放大器中,假定输出电阻为0,这样在放大器内部电压将为0.因为A0是在反馈回路开路时得出的电压增益,所以他定义为开环增益。对于A0为有限的放大器反馈结果将在其他课中讲述。

Practical comstraints limit the ration of R2/R1 to about 10^6:1 maximum. Offset problems, discussed in section 2.15, place an upper limit on R2 and R1 must be large enough compared with the signal source resistance for the latter to be ignored. In practical circuits, R1 usually ranges between 1.0k and 10.0k.

In carrying out the signal analysis it is not necessary to show the DC bias supply, but of course this must be provided.

实际条件限制了R2/R1的值最大只能约为1000:1. 2.15节中讨论的偏置问题限制了R2的上限,而R1与信号源的电阻相比要足够大,以便后者可以忽略不计。在实际电路中,R1通常在1.0-10.0k范围内。在进行信号分析时,没有必要画出直流偏置电压,但这个电压当然是必须的。

The integrator circuit produces an output voltage which is proportional to the integral of the input voltage. This is the inverse mathematical operation to that of differentiation.

The lower limit on the integration is taken as zero time, which of course is arbitrary, and the initial voltage on the capacitor, Vc(0), takes into account all the charge accumulated prior to the chosen time origin. Since the capacitor may be allowed to charge for any arbitrary time t, the upper limit on the integral is the time variable t so that Vc itself is a function of time. This is often shown by use of a ―dummy variable‖for the time in the integrand. Denoting the dummy variable by the symbol t‘, we find that Eq.(2.5) may be written as……

积分器电路产生一个与输入电压的积分成正比例的输出电压,他是微分运算的逆运算。式中积分下限为0,当然这不是强求的。电容的初始电压计及了起始时间之前的所有充电结果。由于电容允许充电到任意时刻t,因此积分上限为时间变量t,这样Vc便为时间t的函数。这一点可以从积分时间中常用哑变量表示看出来。若用符号t‘表示哑变量,可以写成……

However, where there is no risk of confusion, the simpler notation of Eq.(2.5) will be used.

Figure (omitted) shows how the operational voltage amplifier may be arranged as an integrator circuit. Application of the virtual ground concept gives…and….

然而在不发生混淆的情况下,可以使用比较简单的式子。图显示了电压运算放大器怎样被组成积分电路的,由虚地概念可得出。以及与方程联立可得

Thus, the output voltage is proportional to the integral of the input voltage, the constant of proportionality being1/(-RC). This is also the gain of the integrator, and as with the differentiator, it keeps the equation dimensionally correct.

因此,输出电压与输入电压的积分成正比,比例系数为。这也就是积分器增益,对于微分器其量纲也是相同的。

A microcomputer interface converts information between two forms .Outside the microcomputer the information handled by an electronic system exists as a physical signals, but within the program , it is represented numerically . The function of any interface can be broken down into a number of operations which modify the data in some way ,so than the process of conversion between the external and internal forms is carried out in a number or steps.

微机接口实现两种信息形式的交换。在计算机之外,由电子系统所处理的信息以一种物理信号形式存在,但实际程序中,它是用数字表示的。任一接口的功能都可分为以某种形式进行数据变换的一些操作,所以外部和内部形式的转换是由许多步骤完成的。

This can be illustrated by means of an example such as than or Fig 1,which shows an interface between a microcomputer and a transducer producing a continuously variable analog signal. transducers often produce very small out requiring amply frication, or they may generate signals .in a form that needs to be converted again before being handled by the rest of the system .For example ,many transducers these variable resistance which must be converted to a voltage by a special circuit. This process of converting the transducer output into a voltage4 signal which can be connected to the rest of the system is called signal conditioning .In the example of Figure 18.1, the sigma conditioning section translates the range lf voltage or current signals from the transducer to one which can be converted to digital forum by an analog-to-digital converter.

用图一所示的情况为例加以说明,图中展示了微型计算机和产生连续变化信号的传感器之间的接口。但传

Analog-to-digital –digital converter (ADC) is used to convert a continuously variable signal to a corresponding digital forum which can take any one of a fixed number of possible binary values .If the output lf the transducer does not vary continuously ,no ADC is necessary. In this case the signal conditioning section must convert the incoming signal to a form which can be connected directly to the next part of the interface, the input/output section lf the microcomputer itself.

模拟数字转换器(ADC)用来将连续变化的信号变成相应的数字量,这数字量可是可能的二进制数值中的一固定值。如果传感器输出不是连续变化的,就不需要模拟数字转换。这种情况下,信号调理单元必须将输入信号变换成为另一信号。也可直接与接口的下一部分,即微型计算机本身的输入输出单元相连接。

The I/O section converts digital ―on/off‖ voltage signals to a form which can be presented to the processor via the via the system buses .Here the state of each input line whether it is ―on‖ or ―off‖, is indicated by a corresponding ―1‖ or ―0‖.In the line inputs which have been converted to digital form, the patterns of ones and zeros in the internal representation will form binary numbers corresponding to the quantity being converted.

输入输出单员将数字开,关电压信号转换成能通过系统总线传送到计算机的信号形式。这里每一根线的状态,无论是开或关,用相应的1或0 表示。对于已经转换成数字形式的模拟输入量,内部表示中用1和0组成的排列形式形成与被转换量相对应的二进制数。

The―raw‖ numbers from the interface are limited by the design of the interface circuitry and they often require linearization and scaling to produce values suitable for use in the main program. For example ,the interface night be rise to convert temperatures in the range –20 to – +50 dress, buy the numbers produced by an 8-bit converter will lie in the range 0 to 255.Obviously it is easier , the programmer?s point of view to deal directly with temperature rather than to work out the equivalent of any given temperature in terms of the numbers produced by the ADC .Every time the interface is used to read a transducer ,the same operations must be carried out to convert the input number into a more convenient form .Addtionarly ,the operation of some interfaces requires control signals to be passed between the microcomputer and components of the interface ,For these reasons it is normal to use a subroutine to loot after the detailed operation of the interface and carry out any scaling and /or linearization which might be needed.

从接口得到的原数值会受到接口电路设计的限制而且经常需要线性化和量程调整才能形成适合于在主程序中使用的数值。举例来说,接口可用于转换范围在-20度到50度的温度,而八位转换器所产生的数值则在0-255之间。显然,从程序员的观点,对温度进行直接的处理要比使用由ADC产生的与一给定温度相一致的值要容易。接口总是用于读取传感器的值,同时还要将输入数值转换成更便易的形式。而且,接口操作需要将控制信号在微机和接口元件之间进行传送。根据这些理由,通常使用子程序来监督接口的具体操作,并完成任何所需的量程调整和/或线性变化。

Output interfaces take a similar form (Fig.18.2), the biopic difference being that here the flow of information is in the opposite direction; it is passed from the program to the outside world. In this case the program may call an output subroutine which supervises the operation of the interface and performs the scaling numbers which may be needed for a digital-to-analog converter (DAC) .This subroutine passes information in term to an out analog form using a DAC .Finally the signal is conditioned (usually amplified ) to a form suitable for operating an actuator.

输出接口采用相似的形式,明显的差别在于信息流的方向相反;是从程序到外部世界。这种情况下,程序可称为输出程序,它监督接口的操作并完成数字模拟转换器所需数字的标定。该子程序依次送出信息给输出器件,产生相应的电信号,由DAC转换成模拟形式。最后,信号经调理(通常是放大)以形成适应于执行器操作的形式。

The signals used within microcomputer circuits are almost always too small to be connected directly to the ―outside world ‖and some king of interface must be used to translate them to a more appropriate form .The design of section of interface circuits is one of the most important tasks facing the engineer wishing to apply microcomputers. We have seen that in microcomputers information is represented as discrete patterns of bits ;this digital form is most useful when the microcomputer is to be connected to equipment which can only be switched on or off, where each bit might represent the state of a switch or actuator.

在微机电路中使用的信号几乎总是太小而不能直接连接到外部世界,因而必须用某种形式将其转换成更适宜的形式。接口电路部分的设计是使用微机的工程师所面临最重要的任务之一。我们已经了解到微机中,信息以离散的位形式表示。当微机要与只有打开或关闭操作的设备相连接时,这种数字形式是最有用的,这里每一位都可以表示一开关或一执行器的状态。

Care must be taken when connecting logic circuits to ensure that their logic levels and current ratings are compatible .The output voltages produced by a logic circuit are normally specified in terms of worst case values when sourcing or sinking the maximum rated currents .Thus V OH is the guaranteed minimum ―high ‖ voltage when sourcing the maximum rate ―high‖ output current IOH ,while VOL is the guaranteed ―low‖ output voltage when sinking the maximum rated ―low ‖output current IOL .There are corresponding specifications for logic inputs which specify the minimum input voltage which will be recognized as a logic ―high‖ state VIH ,and the maximum input voltage which will be regarded as a logic ―low‖ state VIL.

连接逻辑电路时,必须小心翼翼,以保证他们的逻辑电平和电流额定值是兼容的。有逻辑电路产生的输出电压通以拉出或灌入最大额定电流时,按最弱情况下数值所定义。这样VOH是当拉出最大额定高输出电流IOH 时所允许的最小高电压。而VOH则是当灌入最大额定地输出电流IOL时所允许的最低电压。对逻辑输入也有相应的参数,规定最小输入电压为逻辑高状态VIH,以及最大输出电压为逻辑低状态VIL。

For input interface, perhaps the main problem facing the designer is that of electrical noise .Small noise signal may cause the system to malfunction, while larger amounts of moist can permanently damage it. The designer must be aware of these dangers from the outset. There are many methods to protect interface circuits and microcomputer from various kinds of noise .Following is some examples:

Input and output electrical isolating between the microcomputer system and external devices using an opt-isolator or a transformer.

1.Removing high frequency noise pulses by a low-pea filter and Schmitt-trigger.

1.Protecting against excessive input voltages using a pair of diodes to power supply reversibly biased in normal direction.

对于输入接口,也许设计所面临的主要问题是电噪声,小噪声信号会引起系统工作不良,而大量的噪声会造成永久性的损坏。设计者必须从一开始就清楚这些危险。有许多方法保护接口电路和微机不受各种各样的噪声影响下面是一些例子:1,使用光电隔离或变压器实现微机系统和外部器件之间的输入输出电信号隔离。2用一低通滤波器和一施密特触发器排除高频噪声脉冲。3,用一对二级管以反向偏置于正常方向的形式连接至电源端,来保护过高的输入电压

For output interface, parameters VOH, VOL, IOH and IOL of a logic device are usually much to low to allow loads to be connected directly, and in practice an external circuit must be connected to amplify the current and voltage to drive a load. Although several types of semiconductor devices are now available for controlling DC and AC powers up to many kilowatts, there are two basic ways in which a switch can be connected to a load to control it : series connection and shunt connection as shown in Figure 18.3.

对于输出接口,一逻辑器件的参数VOL,VOH, IOL, IOH,往往太小而不能直接与负载相连,实践中必须在一个外部电路将电流和电压进行放大以驱动一负载。现在尽管有一些类型的半导体器件可用于将DC和AC的功率控制若干千瓦,有两种基本方式将开关连至负载。如图的串联连接和并联连接。

With series connection, the switch allows current to flow through the load when closed, while with shunt connection closing the switch allows current to bypass the load.

Both connections are useful in low-power circuits, but only the series connection can be used in high-power circuits because of the power wasted in the series resistor R.

对于串联连接,开关闭合时使电流流过负载,而当并联连接时和上开关使电流绕过负载。两种方式都可用于低功率电路中,但只有串联连接才能用于高功率电路,这是因为串联电阻R上要消耗功率。

The field of communications is experiencing rapid and dramatic change.Traditionally, telecommunications has been the transmission of information over long distances by means of telephone, teletype, radio, or television. Data communications has been the exchange of data between computer-related devices. Today, these distinctions have blurred as the two have been converging into networks—a group of computers and other devices connected by communication facilities—in which information is processed and communicated in the form of sound, data, and images over common media.

通信技术的领域经历了一个很快的令人瞩目的改变。过去,远程通信通过电话,电报,收音机或者电视。数据通信已经成为了计算机设备之间的数据交换。如今,这个区别已经变得模糊了,因为这两个种类已经被覆盖在网络里一组计算机和其他设备连接的通信设施,一个息处理和流通的地方通过公共媒体以生意数据和图像的方式。

What does this change mean for society? Just as during the late 1800s and early 1900s global societies were shaped by such technologies as ships, electricity, and the internal combustion engine, so in the late 1900s and early 2000s they will be shaped by converging computer and communication technologies. The increased capabilities of the networks allow providers to offer a wider variety of communication services (e.g., video, facsimile, data, and multimedia services) than the traditional voice services. How we obtain news and entertainment, conduct business and education, and accomplish scientific and technical research will all be affected.[

这个改变对于社会意味着什么?就像18世纪末到19世纪早期的社会是由船,电子产品,内燃机等技术组成的。所以20世纪末,到21世纪初他们将会由计算机和通信技术所融合。网络性能的增长允许供应商提供更多样化的通信服务(例如,视频,数据,传真,和多媒体服务)比传统的语音服务。我们如何获得新闻和娱乐,进行商业和教育,实现科学和技术研究都将受到影响。

Networks can be analog, in which information is represented by continuous smoothly varying signals, or digital, in which information is represented by discrete on/off signals.[2]

Digital signals are a newer technology found in computer systems, local area networks, compact disks, and high definition television(HDTV). Digital signals are discrete on/off signals that can be easily stored, compressed, edited, and manipulated. The telephone industry is in the process of converting to an all digital network called Integrated Services Digital Network(ISDN) and similar upgrades are proposed for cellular telephone networks.

网络可以是模拟量,其中的信息是由连续平稳变化的信号,或数字,其中的信息是由离散的开/关信号描绘的。数字信号是一个较新的技术,在计算机系统,局域网,光盘,和高清晰度电视中应用。数字信号是离散的开/关信号,可以很容易地压缩,存储,编辑,和操纵。电话产业是一个改变被称为信号数据的完全数字网络的发生,类似的升级也被提议用在蜂窝式电路网络。

There are three major categories of networks distinguished primarily by geography: wide-area networks , metropolitan-area networks , and local-area networks.

现在有三种通过地域分类成的网络,广域网城域网局域网。

the Internet—a world wide network of computer networks—makes it possible for you to connect your computer (equipped with the appropriate hardware and software)to a wide variety of remote computer. The remote computers may be thousands of miles away, yet you can search libraries of software, access news and other information, conduct business, and meet people with interests or hobbies similar to your own around the globe.

广域网提供了贯穿一个国家或者整个世界的通信,电话网络是一个最普通的例子,他经常被视为一个独立的实体,尽管他是由一类单独的公司建立的。

尽管手机系统创造了一个声音连接在你的电话和世界上任意一部电话之间。网络,一个世界的计算机网络,(配备适当的硬件和软件)使你的计算机连接到一个任意远的计算机成为了可能。远程计算机可能有数千英里之外,你还可以搜索库的软件,获取新闻和其他信息,进行业务,并满足人民的兴趣、联系世界各地有相同爱好的人。

The Internet isn‘t the only worldwide com puter network. International companies have private networks to link offices in different countries together electronically to form 24-hour-a-day business operations. Commercial public networks like CompuServe, Prodigy, and America Online are also used by people around the world. As these networks have grown in popularity, they have begun to interconnect, creating a global collection of people and computers that are able to electronically communicate with one another.[3]

互联网并不是唯一的全球计算机网络,国际公司有专用的网络来连接,把不同国家的办公室连接到一起制定一个24小时都在运作的商业。公共商业网络,如……也同样被全世界的人使用,伴随着这些网络渐渐普及,他们开始互联,创造一个能让全球的人和计算机能以电子方式互相沟通。

Metropolitan-area Networks

Metropolitan-area networks (MANs) provide communications across and among major metropolitan areas such as New York, Chicago, or Los Angeles. Public-safety agencies such as police and fire departments, and dispatch-oriented companies, like Federal Express, operate and maintain their own private networks. They use MANs to allow their mobile ―out-of-offic e‖ workers to talk to and pass data back and forth to one another.

城域网提供通信在主要都市地区如纽约,芝加哥,或洛杉机。公共安全机构如警察和消防部门,和dispatch-oriented公司,像联邦快递,操作和维护他们自己的私人网络。他们用城域网使他们的移动电话和自由活动的工人交谈,来回传递数据到另一个。

more recent development is the public voice and data networks. An example you may be familiar with is the cellular telephone network, which is made possible by dividing a geographical area into hexagonal-shaped cells, each with a base station.[4] Each cell, which is approximately 10 miles(16 kilometers) across, has its own antenna. Like the public telephone network, public MANs eliminate the need for individuals and organizations to build and operate their own networks.

最近的发展是公共数据和语音网络。一个例子是你很熟悉的蜂窝电话网络,这可能是由一块地理区域划分为六角型细胞,每个基站。每一个细胞,这大约是10英里(16公里),有其自己的天线。像公共电话网,公共人的消除需要个人和组织的建立和经营自己的网络。

Local-area Networks

Local-area networks (LANs) provide communications within specific buildings or facilities. This type of network could be used, for example, in a company where computers are located in the sales, accounting, production, and purchasing departments. Each computer would handle the applications unique to its department. When communication among the computers is required, the computers pass data to one another over the network. For example, purchasing information must be passed to the accounting department for inclusion in the accounts payable system, or production-scheduling information must be passed to the purchasing department for use by the purchasing and inventory systems.

局域网(LAN)提供在特定的建筑物或设备通信。这种类型的网络可以使用,例如,在一个公司的电脑都在销售,财务,生产,采购部门。每台计算机都会处理本部门。当计算机之间需要进行通信,计算机通过数据在网络上彼此。例如,采购信息必须传送到会计部列入应付账款,或生产调度信息必须传送到采购部门采购和存货系统使用。

Local-area networks have many different topologies, or ways in which computer can be connected to the network. Today, the two most common topologies are called ring and bus networks.

局域网有多种不同的拓扑结构,使计算机可以连接到网络。今天,两种最常见的拓扑结构可以是环形网络和总线网络

Ring Networks

Computers on a ring network are hooked together one after the other to form one continuous ring. To access each computer, a piece of software called a token is passed around the ring. A token is the electronic equivalent of an envelope. It contains a destination address and a fixed amount of information. The most popular token method is called token passing, in which one token at a time passes from computer to computer and carries messages around the network.

在环形网络中的电脑,是一个一个连接起来的,来形成一个连续不断的环形。为了访问每台电脑,被称作令牌的一系列软件通过周围的环。令牌是电子设备中的信封,它包括了目的地地址和一些固定量的信息。最常用的令牌方法被称为令牌传递,其中一个令牌可以同时向网络中的其他计算机传递信息。

·Bus Networks

On a bus network computers are simply connected by a cable routed along a path in the vicinity of each device that must be connected to it. The most popular bus network is called Ethernet. Bus networks allow multiple messages to be sent simultaneously. This is often accomplished by ―listening‖ to the network to see if any computer is transmitting. If the network is free, the computer can send its data. If two computers accidentally send data at the same time, a collision occurs, and after detecting the collision, the computers wait a random amount of time to transmit again. This access control method goes by the name of Carrier Sense Multiple Access with Collision Detection(CSMA/CD).

在总线型网络上,计算机由一根电缆简单的连接,电缆的路由是按照附近每个必须连接到电缆上的设备所经的路径决定的。最流行的网络称为以太网。总线网络允许多个发送邮件的同时。这通常是通过―听‖到网络上看到的任何计算机发送。如果网络是免费的,计算机可以发送数据。如果电脑不小心发送数据的同时,发生碰撞,碰撞和检测后,电脑等待一个随机时间量再次传送。这种访问控制方法被称为冲突检测的载波侦听多路访问(多址/光盘)

The three major categories of networks are not mutually exclusive. A mobile worker using a portable computer can send a message to a coworker in a cross-country office because the networks can be linked through gateways—devices used to connect dissimilar networks. For example, the mobile worker‘s message might first be transmitted to a local cellular base station, switched to the telephone network and carried across the country to the coworker‘s office, then transferred via gate way into the office LAN.

三大类网络不是相互排斥的。移动工作者使用便携式计算机可以发送一个消息给同事在乡村办公室,由于网络可以通过网关设备用于连接不同网络。例如,移动工作者的消息可能会首先被传送到本地蜂窝基站,切换到电话网络和进行跨国家的同事的办公室,然后通过转移到办公局域网网关。

Local-area networks. Shown in this diagram are the two most common types of networks; token ring, and bus. The networks can be connected via a gateway so any two computers can communicate and share data. In addition, wireless links are possible, and it is possible to communicate to any computer in networks via a modem.

局域网络。图所示是最常见的类型的网络环形网络,总线网络。该网络可以连接通过一个网关,所以任何计算机通讯和共享数据。此外,无线连接是可能的,任何计算机通过调制解调器连接到网络。

Analog and Digital Transducers

As mentioned previously, considerable experience has been accumulated with analog transducers signal conditioning, signal; conditioning, A/D converters etc., and it is natural that the majority of current systems tend to use these techniques. However, there are a number of measuring techniques that are essentially digit in nature,

and which when used as separate measuring instruments require some integral digital circuitry, such as frequency counters and timing circuits, to provide an indicator output. This type of transducer, if coupled to a computer does not necessarily require the same amount of equipment since much of the processing done by the integral circuitry could be programmed and performed and performed by the computer.

前面我们已经提到,人们在模拟转换器、信号调节器和A/D转换器等的使用上已经积累了大量的经验。因此,目前大部分的系统自然都采用这些技术。然而,还有很大一部分测量方法实质是数字的,在个别的测量仪中使用这些方法时,需要用到一些积分电路,如频率计数和计时电路等来提供指示输出。另外,如果把这种转换器和电脑相连的话,就可以省去一些器材;因为很多有积分电路执行的工作可以由计算机程序代为执行。

Collins classifies the signals handled in control and instrumentation systems as follows:

(1) Analog, in which the parameter of the system to be measured although initially derived in an analog form by a sensor is converted to an electrical analog, either by design or inherent in the methods adopted;

(2) Coded digital, in which a parallel digital signal is generated, each bit radix weighted according to some predetermined code. These are referred to in this book as direct digital transducers;

(3) Digital, in which a function, such as mean rate of a repetitive signal, is a measure of the parameter being measured. These are subsequently referred to as frequency domain transducers.

柯林斯把在控制和测量系统中处理的信号分为以下几类:

(1)模拟式。尽管系统的被测数最初通过传感器得到的是模拟信号,然后通过设计或采用原有的方法将模拟形式的信号转换成电模拟信号。

(2)数字码式。产生的信号是并行的数字信号,每一位的基数权重由预先编定的号码系统决定。在本书中这些仪器称作直接数字转换器。

(3)数字式。其中的函数是指测量参数时用到的量度标准,如对重复信号取平均值。这些仪器在后来称为频域转换器。

Some analog transducers are particularly suited to conversion to digital outputs using special techniques. The most popular of these are synchros, and similar devices, which produce a modulated output of a carrier frequency. For ordinary analog use, this output has to be demodulated to provide a signal whose magnitude and sign represent any conventional A/D technique to produce a digital output, there are techniques by which the synchro output can be converted directly to a digital output while providing a high accuracy and resolution, and at a faster rate than is possible in the A/D converter method.

特别地,一些模拟转换器适合用一些特别的技术来把模拟量转换成数字输出。其中最通用的方法是同步法和相似仪器的方法,即产生载波频率的调制输出的方法。在用作普通的模拟量输出仪器时,输出量必须经过解调。解调后输出的是直流信号,支流信号的大小和方向描述了转换器运动元件的偏移。虽然使用传统的

Direct digital transducers are, in fact, few and far between, since there do not seem to be any natural phenomena in which some detectable characteristic changes in discrete intervals as a result of a change of pressure, or change of temperature etc. There are many advantages in using direct digital transducers in ordinary instrumentation systems, even if computers are not used in the complete installation. These advantages are::

(1) The ease of generating, manipulating and storing digital signals, as punched tape, magnetic tape etc.;

(2) The need for high measurement accuracy and discrimination;

(3) The relative immunity of a high level digital signal to external disturbances(noise);

(4) Ergonomic advantages in simplified data presentation(e.g. digital readout avoids interpretation errors in reading scales or graphs).

直接数字转换器实际上用得很少,因为在自然现象中很少有那种由温度变化、压力变化等因素作用而产生的可测量的离散的变化量。在普通的仪器系统中使用直接数字转换器有如下优点(即使在完成安装时不使用计算机):

(1)容易产生、处理和存储信号,如打控带、磁带等;

(2)高精度和高分辨率的需要;

(3)高介数字信号对外部噪声的抗干扰性;

(4)在简化数据描述时的人机工程学优势(例如:数字读出器能避免读刻度或图表时的判度错误)。

The most active development in direct digital transducer has been in shaft encoders, which are used extensively in machine tools and aircraft systems. High resolution and accuracies can be obtained, and these devices may be mechanically coupled to provide a direct digital output of any parameter which gives rise to a measurable physical displacement. The usual disadvantage of these systems is that the inertia of the instrument and encoder often limit the speed of response and therefore the operating frequencies.

在直接数字转换器中最能起作用的发展是轴编码器。轴编码器在机床和飞行系统中被广泛应用。利用这些设备能达到很高的精度和分辨率,而且这些设备能进行激动连接,给出任何可测量物理偏移的直接数字输出。这类系统通常的缺点是仪器的惯性及编码器限制了相应的速度,因而也限制了操作频率。

Frequency domain transducers have a special part to play in online systems with only few variables to be measured, since the computer can act as part of an A/D conversion system and use its own registers and clock for counting pulses or measuring pulse width. Access and process the transducer output. In designing such systems, consideration must be given to the computer time required to access and process the transducer output data.

频域转换器在线系统(测量量较少时)有着特殊的地位。因为计算机能担当A/D转换系统的部分工作,能用它自己的寄存器和时钟来计算脉冲和测量脉冲宽度。在这种系统的设计中必须考虑到计算机存取和处理转换器输出所需的时间。

Information systems combine several functions and devices. These systems provide an approach to the complex problem of measuring, using, and evaluating the mass of data and information produced by modern instrumentation, test, and control installations. Information and data handling systems are the next logical step from centralized control, graphic panels, and, multipoint recording systems. They present many data in logic form and balance the work performed by an operator and the automatic instrumentation system. They are widely used in industrial processes, test cells, and research and development laboratories to save time, increase accuracy of readings, reduce human error, and release skilled technicians for more important duties.

信息系统结合了许多功能和装置。这些系统提供了一个方法的复杂问题的测量,使用,和评价的质量数据和信息生产的现代仪器,测试,控制装置。信息和数据处理系统是一个合乎逻辑的步骤,从集中控制,图形板,和,多点记录系统。他们目前的许多数据在逻辑形式和平衡的工作由一个操作员和自动化仪表系统。它们被广泛应用于工业过程,测试细胞,并研究开发实验室,节省时间,提高数据的准确性,减少人为错误,并释放技术更重要的职责。

The following five major functions are performed by information handling systems:

(1)automation measuring, the continuous and automatic switching of each input signal sequentially to the

measuring circuit and readout system;

(2)automatic logging, the continuous readout and display of all variables measured;

(3)alarm monitoring, the continuous measurement and comparison of the measured variables with a

preset value or limit and an audio or visual indication or alarm of all off-normal(out-of-limit)points;

(4)data and alarm scanning, provides a sequential measurement and review of data and alarm points at a

central location with selective readout and display;

(5)low-speed and high-speed digital data handling systems, combine functions of measuring, logging,

monitoring, scanning, and simple computation (linearizing, square-root extraction, totalizing, scaling)

with selection of a variety of analog and digital display forms.

以下五个主要功能是由信息处理系统:

(1)自动化测量,连续自动开关的每个输入信号顺序测量电路和读出系统;

(2)自动记录,连续读出和显示所有变量测量;

(3)监控报警,连续测量和比较测量变量与预设值或限制和音频或视觉报警指示或所有非正常(极限)点;

(4)数据和报警扫描,提供了一个连续的测量和审查数据和报警点在一个中央位置有选择性地读出和显示;

(5)低速和高速数字数据处理系统,结合功能的测量,记录,监测,扫描,和简单的计算(线性,平

The typical data handling system components and their functions are:

1.Transducers for converting measured variable into convenient electrical voltage or current input signal for

transmission to central room, e.g., thermocouples, resistance thermometers, electrical pressured transducers, stain gages, electrical flow transducers and pneumatic pressure to current converters.

2.Input selector switches to funnel many input information channels switching sequentially to measuring

circuit, e.g., telephone stepping switches, crossbar switches, mercury jet switches, electromechanical switching, electronic multiplexers and manual selector for operator control.

3.Signal conditioning: scaler to adjust some signals to common input value, amplifier to build up low-level

signals, linearizer to remove any nonlinearizer, special bridge balance circuit for certain transducers and analog to digital converter for those analog input signals which will be required for digital readout.

4.Measuring circuit, where the measured variable is actually measured. Servoo-perated null-balance

potentiometer, digital potentiometer with mercury-wetted relay switching, and electronic detector.

5.System programmer, the heart of the system, for it controls the whole system, establishes the routine of the

instrument, selects measuring circuits, switches point, initiates logging and alarms, and provides time information.

6.Readout programmer, actuates readout and display devices.

7.Readout and display, provides means of logging and displaying all variables, recording off-normal points,

recording computed values on analog strip charts, typewriter log sheets, digital display lights, paper punched tape, magnetic tape, oscillograph record, printed tape and punched card.

8.Input signal scaling, span adjustment, zero adjustment, alarm set-point adjustment (by mechanical means),

potentiometers, pinboards, and fixed resistors.

9.Special computation circuits for averaging, multiplying, dividing, and totalizing. These are functions anf

components incorporated in information systems.

典型的数据处理系统的组成及功能:

1。传感器转换成便于测量变量的电压或电流输入信号传输到中央室,例如,热电偶,电阻温度计,电压力传感器,应变片,电流量传感器、气动压力电流转换器。

2。输入选择器开关漏斗多输入信息渠道交换顺序测量电路,例如,电话交换机加强,交叉开关,水银射流开关,机电开关,电子多路复用器和手动选择操作控制。

3。信号调理:缩放调整信号共同的输入值,建立低水平信号放大器,线性化,消除任何非线性,特殊桥梁平衡电路若干传感器和模拟数字转换器的模拟输入信号,将所需的数字读出。

4。测量电路,在测量变量实际上是衡量。伺服传动阀,调零电位器,数字电位器与汞润继电器开关,电子探测器。

5。系统程序员,系统的心脏,它控制整个系统,建立常规的仪器,以测量电路,开关,启动日志和警报,并提供时间信息。

6。读出编程器,读出和显示设备的驱动。

7。读出和显示,提供了手段,记录和显示的所有变量,记录正常点,记录计算值模拟条图,打字机记录表,数字显示灯,纸打孔磁带,磁带,示波器记录,印刷带和穿孔卡片。

8。输入信号缩放,调整,调零,报警设定点调整(通过机械手段),电位器,插接板,固定电阻器。

9。特殊计算电路平均,乘法,分割,和整体性。这些功能和组成部分纳入信息系统。

According to the Encyclopedia Americana,a system is "an aggregation ox assemblage of things so combined by nature or man as to form an integral and complex whale". Mathematical systems theory is the study,of the interruptions and behavior of such an assemblage of "things'* when subjected to certain conditions or inputs. The abstract nature of systems theory is due to the fact that it is concerned with mathematical properties rather than the physical faun of the constituent parts.

按照美工大百科全书的解释,所谓系统就是指“一个各种物体的集合,格局其他性质或人的愿望而结合起来以致形成一个集中、复杂的整体”。数学中的系统理论,就是对这种由若干“物体”过程的集合,当其受到某些条件和输入作用的影响后的行为和阻断进行研究的一门学问。系统理论的抽象性质源于这样的一个事实:系统理论更关心物体组成的部件的数学性质而不是其物理形式。

Control theory is mare often concerned with physical applications. A control system is considered to he any system which exists for the purpose or regulating or controlling the flow of energy,information, money,or other quantities in some desired fashion. In more general terms,a control system is an interconnection of many components or functional units in such a way as to produce a desired result. In this book,control theory is assumed to encompass all questions related to design and analysis of control systems.

控制理论通常与实际应用有关。一般认为,控制系统是任意一个这样的系统,其目的是为了以某种期望的方式来调节或控制诸如能量,信息,资金等等物理量的流动。从更一般的意义上讲,控制系统就是一个按照一定方式由很多元件或功能单元构成的结合体,期目的是为了获得期望的结果。本书中假定控制理论包括所有与控制理论包括所有系统设计和分析问题有关的内容。

Fig. 37. 1 is a general representation of an open loop control system, the ingot or control u(t) is selected hayed on the goals for the system and all available a priori knowledge about the system, The input is in no way influenced by the output of the system,represented by y(t),If unexpected disturbances act upon an open-loop system, or if its behavior is not completely understood,them the output will not behave precisely as expected.

图37.1是对对开环控制系统的一般性表示。输入变量或控制作用u(t)是根据本系统的目标以及所

Another general class of control systems is the closed-loop or f feedback control system,as illustrated in Fig.

37. 2, to the closed-loop system, the control u(t) is modified in some way by information about the behavior of the system output, A feedback system is often better able to cope with unexpected disturbances and uncertainties about the system's dynamic behavior.

另一类常见的控制系统是闭环或反馈控制系统,如图37.2所示。闭环控制系统中,控制作用u(t)被以某种方式由于系统输出行为的信息所校正。一个反馈系统经常能更好的应付不期望的扰动作用以及系统动态性能的不确定性。

However,it need not be true that closed-look control is always superior to open-loop control. When the measured output has errors which are sufficiently large,and when unexpected disturbances are relatively unimportant,closed-loop control can have a performance which is inferior to open-loop control.

而闭环控制并不一定总是优于开环控制。当输出的测量误差足够大或不期望的扰动无关紧要时,闭环控制的性能就会比开环控制的差。

Introduction to Modern Control Theory

Several factors provided the stimulus for the development of modern control theory:

(a) The necessity of dealing with more realistic models of systems,

(b) The shift in emphasis towards optimal control and optimal system design.

(c)The continuing developments in digital computer technology.

(d)Tine shortcomings of previous approaches.

(e)A recognition of the applicability of well-known methods ire other fields of knowledge.

现代控制理论讨论有几个因素激励了现代控制理论的发展:(a)处理更加真实的系统模型的必要性。(b)研究重点向最优化控制和最优化系统设计的转移。(c)数字计算机技术的不断发展。(d)以前的办法的缺陷。(e)对于将熟知方法在其他知识领域中应用的广泛认同。

The transition from simple approximate models, which are easy to work with., to more realistic models produces two effects. First .a larger number of variables must be included in the model. Second,a mare realistic model is mare likely to captain nonlinearities and time-varying parameters. Previously ignored aspects of the system, such as interactions and feedback through the environment,are more likely to be included. With an advancing technological society,there is a trend towards more ambitious goals. This also means dealing with complex systems with a larger number of interacting components. The need for greater accuracy and efficiency has changed the emphasis on control system performance. The classical specifications in terms of percent overshoot, settling time, bandwidth, etc.,have in many cases given way to optimal criteria such as minimum energy,minimum cost,nd minimum time operation. Optimization of these criteria makes it even more difficult to avoid dealing with unpleasant nonlinearities. Optimal control theory often dictates that nonlinear time-varying control laws he used, even if the basic system is linear and time-invariant.

这种从简单、易用的近似模型到更加真实模型的转移产生了两个方面的影响:首先,模型中必须包含众多的变量;其次,更为真实的模型往往具有非线性个时变参数。以前往往忽略的一些系统问题,例如关联问题以及通过环境形成反馈等,现在却需要考虑。在不断发展先进技术的社会中朝着更加宏伟目标的发展趋势是很明显的。这就意味着要处理具有大量相互关联部件的复杂系统。对于更加精确和更加有效的需求已经改变了对控制系统性能要求的重点。以百分超调量、调节时间、带宽等来表示的精雕技术指标已经在很多场合让位于最优性准则,例如最小能耗、最低成本和最短时间操作等。依据这些准则的最优化似的想要避免处理讨厌的非线性一事变得更为困难。即使基本受控系统式线性和时不变的,最优化控制理论也经常规定要采用非线性,时变的控制规律。

The continuing advances in computer technology have had three principal effects on the controls field. one of these relates to the gigantic supercomputers. The size and class of problems that can now be modeled,analyzed,and controlled are considerably larger than they were when the first of this hook was written.

计算机技术的不断发展,已经对控制领域产生了三个方面的主要影响。影响之一与超大规模的巨型机有关。现在能够进行建模、分析和控制研究的问题的规模和困难级别都已经大大超过了本书的第一版的情况。

The second impact of computer technology has to do with the proliferation and wide availability of microcomputers in homes and in the work place. Classical control theory was dominated by graphical methods because at the time that was the only way to solve certain problems. Now every control designer has easy access to powerful computer packages for system analysis and design. The old graphic methods have not yet disappeared,but have been automated. They survive because of the insight and intuition that they can provide. However,some different techniques are often better suited to a computer. Although a computer can he used to carry out the classical transform-inverse transform methods, it is usually more efficient for a computer to integrate differential equations directly,

计算机技术的第二个影响与微型机在数量上的激增以及其在家庭、工作场所随处可用的便利性紧密相关。经典控制理论中图解方法占主导地位,这是因为当时图解式解决某些问题的唯一方法。现在,每一个控制工程设计人员都很容易获得功能强大的计算机软件包,用于进行系统的分析和设计工作。老的图解方法并没有消亡,不过已经能够自动进行工作了。他们之所以仍然存在的原因是其多具有的直观性和指导性。然而,一些完全不同的技术经常对计算机更加适合。尽管计算机课用于执行经典的变换-反变换运算,然而用计算机对微分方程直接进行积分则往往更加有效。

The third major impact of computers is that they are now so commonly used as just another component in the control system. Their cost, size and reliability make it possible to use them routinely in many systems. This means

Modern control theory LS well suited to the above trends because its time-domain techniques and its mathematical language (matrices,linear vector space, etc.) are ideal when dealing with a computer. Computers are a major reason for the existence of state variable methods.

现代控制理论特别适应上述的发展趋势。这是因为时间域技术及其数学表达语言(例如矩阵、线性向量空间等)在计算机上应用是非常理想的。计算机的发展也是状态变量方法之所以会产生的一个主要原因。

Most classical control techniques were developed for linear constant coefficient systems with one input and one output(perhaps a few inputs and outputs).The language of classical techniques is the Laplace or z-transform and transfer functions. When nonlinearities and time variations are present,the very basic for these classical techniques is removed. Some successful techniques such as phase-plane methods,describing functions and other ad hoc methods,have been developed to alleviate this shortcoming. However the greatest success has been limited to low-order systems. The state variable approach of modern control theory provides a uniform and powerful method of representing systems of arbitrary order,linear or nonlinear,with time-varying or constant coefficients. It provides an ideal formulation for computer implementation and is responsible for much of the progress its optimization theory.

大多数经典控制技术都是带有一个输入、一个输出(也许可有数个输入和输出)的线性、常系数系统而发展起来的。经典技术的表述语言是拉普拉斯或z变换以及传递函数。一旦出现非线性和时变性,经典技术最根本的基础就不复存在了。诸如相平面方法、描述函数法和其他有关方法这样一些很成功的技术能够得以发展的原因就是为了弥补这个短处。然而经典控制理论最大的成功也是局限于低阶系统中。现代控制理论的状态变量法提供了一种统一、高效的方法来描述具有任意阶次、线性或非线性、时变或常系数的各种系统。它也为计算机处理提供了一种理想的表达方法,并引起了许多方面的最优化理论的进展。

Modern control theory is a recent development in the field of control. Therefore,the name is justified at least as a descriptive title. However, the foundation of modern control theory is to be found in other well-established fields, representing a system in terms of state variables is equivalent to the approach of Hamiltonian mechanics,using generalized coordinates end generalized moments. The advantages of this approach have been well-known in classical physics for many years. The advantages of using matrices when deals with simultaneous equations of carious kinds have long been appreciated in applied mathematics. The field of linear algebra also contributes heavily to modern control theory. This due to the concise notation,the generality of the results,and the economy of thought that linear algebra provides.

现代控制理论是在控制领域中的新发展。因此可以说它是名副其实。然而现代控制理论的基础却应该在其他一些发展成熟的领域中寻找。以状态变量形式来表示一个系统的方法完全等价于再其他哈密尔顿力学中采用通用坐标和通用动量的方法。这种方法的优越性在经典物理学中多年来已经众所周知。当处理各种联立方程式采用矩阵的好处在应用数学领域中也已久为人知。线性代数对现代控制理论的发展更是功不可没。其原因在于线性代数所提供的简洁的表达、通用的结果以及高效的思路。

If we examine the word control, we find several meanings given in dictionary, e.g. command, direct, govern, and regulate. Thus, a control system may be regarded as a group of physical components arranged to direct the flow of energy to a machine or process in such a manner as to achieve the desired performance.

The word automatic means self-moving or self-acting; thus an automatic control system is a self-acting control system.

如果查询单词控制,我们会在字典中找到一些意思:命令,执行,管理和规范。因此控制系统可以称为是一组物理器件组合在一起执行机械或者程序的能量流动,从而获得给定特性。

自动这个单词的意思是自运动,自动做,因此一个自动控制系统是自动做控制系统。

An important distinction applied to control systems, whether automatic or otherwise, is that between open-loop and closed-loop operation. Automatic control, including this distinction, can perhaps be best introduced by means of a simple example.

不管是自动还是其他种类,控制系统的一个重要区别是开环控制还是闭环控制。自动控制包涵这种区别可以通过一个简单的例子来做最好的介绍。

Assumed that the oven shown in Fig.8.1 is heated by an electric heater controlled by a switch that provides several levels of current to the heating element. The setting of the switch represents the input quantity since it activates the system to produce the output. The temperature of the oven is the output or controlled quantity. Since the current to the heater is the quantity being altered, we can think of it as manipulated quantity.

假设图中所示的炉被电热器加热,加热器由一个给加热元件提供几个档位电流的开关控制。开关的位置代表输入量因为他驱动系统从而产生输出。炉的温度是输出或者被控制量。由于加热器的电流是该变量,我们可以认为他是控制量。

For a given setting of the control switch the oven temperature will reach a value related to the heater current and heat losses through the oven walls. If the temperature is unsatisfactory, this fact by itself can in no way alter the input to the oven control. Thus it can be said that the output quantity has no effect on the input quantity. The control in this case is identified as an open-loop control system. If some condition such as the ambient temperature surrounding the oven should change, the oven temperature will also change. Thus the open-loop control system cannot correct for changes that disturb the controlled quantity.

对于一个给定的开关控制设置,炉的温度会达到一个与加热电流和通过炉壁损失的热量有关的值。如果温度不理想,这种情况下他自己无法改变输入来控制。因此这被称为输出量对输入量没有影响。这种控制被称为开环控制系统。如果一些情况,炉周围的环境温度改变,炉的温度也会改变。因此开环控制系统不能校正由

A human being can be added to the system for the purpose of maintaining the oven temperature at a desired value. This is shown in Fig.8.2. By observing a thermometer within the over, the person could alter the position of the control switch to more nearly achieve the required temperature. It is important to note that the addition of the human operator has provided a means by which the output is fed back and compared with the desired value. Actual control of the heating element depends on the error or deference between the desired and actual temperatures. Any necessary change is made in the direction of reducing this error. For example, if the temperature were low, the heater current would be increased to provide more heat.

人可以被添加到系统中从而达到维持炉温在期望值的目的。图所示通过观察炉里的温度计人可以改变控制开关的位置从而更接近的获得需要温度。特别强调的是,人的参与提供了一种输出量反馈到输入并与期望值相比较的方法。实际控制加热元件依靠期望温度和实际温度之间的差异。指挥中通过任何必要的改变来减少误差。例如,如果温度降低,加热电流就要增加来提供更多的热量。

Systems in which the output has an effect upon the input are called closed-loop control systems or, more commonly, feedback controls systems. The feedback capture of the system in Fig.8.2 may be seen by tracing the closed-loop. The function of comparing the actual temperature with the desired value is performed in the mind of the operator, and the command is executed by the response of his muscles. Even though close-loop control of the oven is established by the operator, the results may be less then satisfactory. The temperature will cycle above and blew the desired value as the operator adjusts the switch even though the excursions would tend to decrease with operator experience. A change in the level of the power source or in the ambient temperature surrounding the oven would adversely affect the system‘s output. In addition, watching a thermometer and operating a switch would be a dull and time-consuming task. This arrangement could be described as a manual closed-loop control system.

输出对输入有影响的系统称之为闭环控制系统,或者更通俗的称为反馈控制系统。图中,通过跟踪闭环系统可以看到反馈的本质。比较实际温度和期望温度的功能是在操作者的大脑中完成的,命令通过他的肌肉执行。即使炉的闭环控制系统由人建立,结果可能并不理想,操作者调整开关即使偏差会趋于减小随着操作者的经验,温度仍然会在期望值上下浮动。电源电平的改变或是炉周围环境温度的改变,会不利的影响系统的输出,另外观察温度计和控制开关是一种枯燥又费时的任务,这个方案可以称为手动闭环控制系统。

To further improve performance and obtain more precise control, the human may be replaced by a mechanical, electrical, or other form of comparisons and control unit. Fig8.3 shows, on the automatic basic, that is, without human intervention. The temperature is now measured by a thermocouple, a device that generates an electrical voltage proportional to temperature. This voltage is fed back and compared with a reference voltage that represents the desired temperature. The difference between the two voltages is amplified electronically and controls the current to the heating element. Since the voltage feedback is subtracted from the reference voltage, it is known as a negative-feedback signal.

为了更加提高性能并且获得更加精确地控制,人可以被机械的、电气的或者其他形式比较和控制单元代替。图所示在自动的基础上即没有人的参与,温度由温度计测量,这个设备产生与温度成比例的电压,这个电压反馈到代表期望温度的参考电压并与之比较。这两个电压之差被电气放大,并且控制加热元件的电流由于电压反馈是从参考电压中减去的,它被称为是负反馈信号。

The example has illustrated how automatic closed-loop control is employed to perform a task more rapidly and consistently than can be accomplished by a human being. The use of negative feedback in a closed-loop control system tends to maintain a desired value of a quantity or condition by measuring the existing value, comparing it to the desired value, and using the difference as a means of initiating action to reduce the difference. The negative-feedback concept has become the foundation for automatic-control-system design.

这个例子说明了自动闭环控制可以比人参与完成的控制更快更稳定的完成一个任务。闭环控制系统中负反馈的应用趋向于维持一个量在期望值或是这样一个状态:通过测量实际值并与期望值相比较,然后用差别作为启动动作来减小差别。负反馈概念已经成为自动控制设计的基础。

电气专业英语论文

Page1 Electrical Energy Transmission(电能输送) From reference 1 Growing populations and industrializing countries create huge needs for electrical energy. Unfortunately, electricity is not always used in the same place that it is produced, meaning long-distance transmission lines and distribution systems are necessary. But transmitting electricity over distance and via networks involves energy loss. So, with growing demand comes the need to minimize this loss to achieve two main goals: reduce resource consumption while delivering more power to users. Reducing consumption can be done in at least two ways: deliver electrical energy more efficiently and change consumer habits. Transmission and distribution of electrical energy require cables and power transformers, which create three types of energy loss: the Joule effect, where energy is lost as heat in the conductor (a copper wire, for example); magnetic losses, where energy dissipates into a magnetic field; the dielectric effect, where energy is absorbed in the insulating material. The Joule effect in transmission cables accounts for losses of about 2.5 % while the losses in transformers range between 1 % and 2 % (depending on the type and ratings of the transformer). So, saving just 1 % on the electrical energy produced by a power plant of 1 000 megawatts means transmitting 10 MW more to consumers, which is far from negligible: with the same energy we can supply 1 000 - 2 000 more homes. Changing consumer habits involves awareness-raising programmers, often undertaken by governments or activist groups. Simple things, such as turning off lights in unoccupied rooms, or switching off the television at night (not just putting it into standby mode), or setting tasks such as laundry for non-peak hours are but a few examples among the myriad of possibilities. On the energy production side, building more efficient transmission and

化学专业英语(修订版)翻译

01 THE ELEMENTS AND THE PERIODIC TABLE 01 元素和元素周期表 The number of protons in the nucleus of an atom is referred to as the atomic number, or proton number, Z. The number of electrons in an electrically neutral atom is also equal to the atomic number, Z. The total mass of an atom is determined very nearly by the total number of protons and neutrons in its nucleus. This total is called the mass number, A. The number of neutrons in an atom, the neutron number, is given by the quantity A-Z. 质子的数量在一个原子的核被称为原子序数,或质子数、周淑金、电子的数量在一个电中性原子也等于原子序数松山机场的总质量的原子做出很近的总数的质子和中子在它的核心。这个总数被称为大量胡逸舟、中子的数量在一个原子,中子数,给出了a - z的数量。 The term element refers to, a pure substance with atoms all of a single kind. T o the chemist the "kind" of atom is specified by its atomic number, since this is the property that determines its chemical behavior. At present all the atoms from Z = 1 to Z = 107 are known; there are 107 chemical elements. Each chemical element has been given a name and a distinctive symbol. For most elements the symbol is simply the abbreviated form of the English name consisting of one or two letters, for example: 这个术语是指元素,一个纯物质与原子组成一个单一的善良。在药房“客气”原子的原子数来确定它,因为它的性质是决定其化学行为。目前所有原子和Z = 1 a到Z = 107是知道的;有107种化学元素。每一种化学元素起了一个名字和独特的象征。对于大多数元素都仅仅是一个象征的英文名称缩写形式,一个或两个字母组成,例如: oxygen==O nitrogen == N neon==Ne magnesium == Mg

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电气毕业论文英语文献原文 翻译

外文翻译院(系) 专业班级 姓名 学号 指导教师 年月日

Programmable designed for electro-pneumatic systems controller John F.Wakerly This project deals with the study of electro-pneumatic systems and the programmable controller that provides an effective and easy way to control the sequence of the pneumatic actuators movement and the states of pneumatic system. The project of a specific controller for pneumatic applications join the study of automation design and the control processing of pneumatic systems with the electronic design based on microcontrollers to implement the resources of the controller. 1. Introduction The automation systems that use electro-pneumatic technology are formed mainly by three kinds of elements: actuators or motors, sensors or buttons and control elements like valves. Nowadays, most of the control elements used to execute the logic of the system were substituted by the Programmable Logic Controller (PLC). Sensors and switches are plugged as inputs and the direct control valves for the actuators are plugged as outputs. An internal program executes all the logic necessary to the sequence of the movements, simulates other components like counter, timer and control the status of the system. With the use of the PLC, the project wins agility, because it is possible to create and simulate the system as many times as needed. Therefore, time can be saved, risk of mistakes reduced and complexity can be increased using the same elements. A conventional PLC, that is possible to find on the market from many companies, offers many resources to control not only pneumatic systems, but all kinds of system that uses electrical components. The PLC can be very versatile and robust to be applied in many kinds of application in the industry or even security system and automation of buildings.

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[实用参考]大学英语精读第三版第四册课文及课文翻译.doc

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物质由分子通过分子间的吸引力紧紧地靠在一起。当物质吸收热量,分子的能量升级并且 使得分子之间的间隙增大。当越来越多的能量被吸收,这种效果就会加剧,粒子之间相互脱离。这种由固态到液态的状态变化通常被称之为熔化。 当液体吸收了更多的热量时,一些分子获得了足够多的能量而从表面脱离,这个过程 被称为蒸发(凭此洒在地面的水会逐渐的消失在蒸发的过程中,一些分子是在相当低的 温度下脱离的,然而随着温度的上升,分子更加迅速的脱离,并且在某一温度上液体内部 变得非常剧烈,大量的气泡向液体表面升起。在这时我们称液体开始沸腾。这个过程是变为蒸汽的过程,也就是液体处于汽化状态。 让我们试想大量的水装在一个敞开的容器内。液体表面的空气对液体施加了一定的压 力,随着液体温度的上升,便会有足够的能量使得表面的分子挣脱出去,水这时开始改变 自身的状态,变成蒸汽。在此条件下获得更多的热量将不会引起温度上的明显变化。所增 加的能量只是被用来改变液体的状态。它的效用不能用温度计测量出来,但是它仍然发生 着。正因为如此,它被称为是潜在的,而不是可认知的热量。使这一现象发生的温度被称为是沸点。在常温常压下,水的沸点为100摄氏度。 如果液体表面的压力上升, 需要更多的能量才可以使得水变为蒸汽的状态。 换句话说, 必须使得温度更高才可以使它沸腾。总而言之,如果大气压力比正常值升高百分之十,水必须被加热到一百零二度才可以使之沸腾。

应用化学专业英语翻译完整篇

1 Unit5元素周期表 As our picture of the atom becomes more detailed 随着我们对原子的描述越来越详尽,我们发现我们陷入了进退两难之境。有超过100多中元素要处理,我们怎么能记的住所有的信息?有一种方法就是使用元素周期表。这个周期表包含元素的所有信息。它记录了元素中所含的质子数和电子数,它能让我们算出大多数元素的同位素的中子数。它甚至有各个元素原子的电子怎么排列。最神奇的是,周期表是在人们不知道原子中存在质子、中子和电子的情况下发明的。Not long after Dalton presented his model for atom( )在道尔顿提出他的原子模型(原子是是一个不可分割的粒子,其质量决定了它的身份)不久,化学家门开始根据原子的质量将原子列表。在制定像这些元素表时候,他们观察到在元素中的格局分布。例如,人们可以清楚的看到在具体间隔的元素有着相似的性质。在当时知道的大约60种元素中,第二个和第九个表现出相似的性质,第三个和第十个,第四个和第十一个等都具有相似的性质。 In 1869,Dmitri Ivanovich Mendeleev,a Russian chemist, 在1869年,Dmitri Ivanovich Mendeleev ,一个俄罗斯的化学家,发表了他的元素周期表。Mendeleev通过考虑原子重量和元素的某些特性的周期性准备了他的周期表。这些元素的排列顺序先是按原子质量的增加,,一些情况中, Mendeleev把稍微重写的元素放在轻的那个前面.他这样做只是为了同一列中的元素能具有相似的性质.例如,他把碲(原子质量为128)防在碘(原子质量为127)前面因为碲性质上和硫磺和硒相似, 而碘和氯和溴相似. Mendeleev left a number of gaps in his table.Instead of Mendeleev在他的周期表中留下了一些空白。他非但没有将那些空白看成是缺憾,反而大胆的预测还存在着仍未被发现的元素。更进一步,他甚至预测出那些一些缺失元素的性质出来。在接下来的几年里,随着新元素的发现,里面的许多空格都被填满。这些性质也和Mendeleev所预测的极为接近。这巨大创新的预计值导致了Mendeleev的周期表为人们所接受。 It is known that properties of an element depend mainly on the number of electrons in the outermost energy level of the atoms of the element. 我们现在所知道的元素的性质主要取决于元素原子最外层能量能级的电子数。钠原子最外层能量能级(第三层)有一个电子,锂原子最外层能量能级(第二层)有一个电子。钠和锂的化学性质相似。氦原子和氖原子外层能级上是满的,这两种都是惰性气体,也就是他们不容易进行化学反应。很明显,有着相同电子结构(电子分布)的元素的不仅有着相似的化学性质,而且某些结构也表现比其他元素稳定(不那么活泼) In Mendeleev’s table,the elements were arranged by atomic weights for 在Mendeleev的表中,元素大部分是按照原子数来排列的,这个排列揭示了化学性质的周期性。因为电子数决定元素的化学性质,电子数也应该(现在也确实)决定周期表的顺序。在现代的周期表中,元素是根据原子质量来排列的。记住,这个数字表示了在元素的中性原子中的质子数和电子数。现在的周期表是按照原子数的递增排列,Mendeleev的周期表是按照原子质量的递增排列,彼此平行是由于原子量的增加。只有在一些情况下(Mendeleev注释的那样)重量和顺序不符合。因为原子质量是质子和中子质量的加和,故原子量并不完全随原子序数的增加而增加。原子序数低的原子的中子数有可能比原子序数高的原

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