自动化专业英语期末复习课文与翻译.doc

. An electrical circuit or network is composed of elements such as resistors , inductors , and capacitors connected together in some manner .If the network contains no energy sources , such asbatteries or electrical generators,it is known as a passive network.On the other hand, if one or more energy sources are present , the resultant combination is an active network. In studying the behavior of an electrical network,we are interested in determining the voltages and currents that exist within the circuit. Since a network is composed of passive circuit elements,we must first define the electrical characteristics of these elements.电路或电网络由以某种方式连接的电阻器、电感器和电容器等元件组成。如果网络不包含能源，如电池或发电机，那么就被称作无源网络。换句话说，如果存在一个或多个能源，那么组合的结果为有源网络。在研究电网络的特性时，我们感兴趣的是确定电路中的电压和电流。因为网络由无源电路元件组成，所以必须首先定义这些元件的电特性. In the case of a resistor, the voltage-current relationship is given by Ohms law, which ststes that the voltage across the resistor is equal to the current through the resistor multiplied by the value of the resistance. Mathematically, this is expressed as u=iR where u=voltage , V; i=current, A; R=resistance .就电阻来说，电压-电流的关系由欧姆定律给出，欧姆定律指出：电阻两端的电压等于电阻上流过的电流乘以电阻值。在数学上表达为:u=iR (1-1A-1)式中 u=电压，伏特；i =电流，安培；R = 电阻，欧姆。 The voltage across a pure inductor is defined by Faradays law ,which states that the voltage across the inductor is proportional to the rate of change with time of the current through the inductor. Thus we have u=Ldi/dt where di/dt=rate of change of current ,A/s; L=inductance ,H. 纯电感电压由法拉第定律定义，法拉第定律指出：电感两端的电压正比于流过电感的电流随时间的变化率。因此可得到：U=Ldi/dt 式中 di/dt = 电流变化率， 安培/秒； L = 感应系数， 享利。 The voltage developed across a capacitor is proportional to the electric charge q accumulating on the plates of the capacitor. Since the accumulation of charge may be expressed as the summation, or integral , of the charge increments dq, we have the equation u=1/c fdq where the capacitance C is the proportionality constant relating voltage and charge. By definition, current equals the rate of change of charge with time and is expressed as i=dq/dt. Thus an increment of charge dq is equal to the current multiplied by the corresponding time increment, or dq=i dt. 电容两端建立的电压正比于电容两极板上积累的电荷q 。因为电荷的积累可表示为电荷增量dq的和或积分，因此得到的等式为 u= 1/c fdq，式中电容量C是与电压和电荷相关的比例常数。由定义可知，电流等于电荷随时间的变化率，可表示为i = dq/dt。因此电荷增量dq 等于电流乘以相应的时间增量，或dq = i dt， 那么等式 (1-1A-3) 可写为式中 C = 电容量，法拉。 A common method of analyzing an electrical network is mesh or loop analysis. The fundamental law that is applied in this method is Kirchhoffs first law, which states that the algebraic sun of the voltages around a closed loop is 0 ,or , in any closed loop , the sum of the voltage rises must equal the sum of the voltage drops. Mesh analysis consists of assuming that currents-termed loop currents-flow in each loop of a network ,algebraically summing the voltage drops around each loop ,and setting each sum equal to 0. 分析电网络的一般方法是网孔分析法或回路分析法。应用于此方法的基本定律是基尔霍夫第一定律，基尔霍夫第一定律指出：一个闭合回路中的电压代数和为0，换句话说，任一闭合回路中的电压升等于电压降。网孔分析指的是：假设有一个电流即所谓的回路电流流过电路中的每一个回 路，求每一个回路电压降的代数和，并令其为零 One problem with electronic devices corresponding to the generalized amplifiers is that the gains, Au or Ai, depend upon internal properties of the two-port system(u,，Ri ,Ro, etc). This makes design difficult since these parameters usually vary from device ,as well as with temperature. The operational amplifier, or Op-Amp, is designed to minimize this dependence and to maximze the ease of design. An Op-Amp is an integrated circuit that has many component parts such as resistors and transistors built into the device. At this point we will make no attempt to describe these inner workings. 运算放大器像广义放大器这样的电子器件存在的一个问题就是它们的增益AU或AI取决于双端口系统(m、b、RI、Ro,等)的内部特性。器件之间参数的分散性和温度漂移给设计工作增加了难度。设计运算放大器或Op-Amp的目的就是使它尽可能的减少对其内部参数的依赖性、最大程度地简化设计工作。运算放大器是一个集成电路，在它内部有许多电阻、晶体管等元件。就此而言，我们不再描述这些元件的内部工作原理。 Integrated circuit technology allows construction of many amplifier circuits on a single composite chip of semiconductor material.集成电路技术使得在非常小的一块半导体材料的复合 “芯片”上可以安装许多放大器电路。 The first law states that in normal Op-Amp circuits we may assume that the voltage difference between the input terminals is zero, that is , U+=U-第一个定律指出：在一般运算放大器电路中，可以假设输入 端间的电压为零，也就是说U+=U-The second law states that in normal Op-Amp circuits both of the input currents may be assumed to be zero: I+=I-=0第二个定律指出：在一般运算放大器电路中，两个输入电流可被假定为零：I+=I-=0 The two-valued variables which we have been discussing are often called logical variables, while the operations such as the OR operation and the AND operation are referred to as logical operations. We shall now briefly discuss the relevance of such terminology, and in so doing we shall bing out the special aptness of the designations true and false to identify the possible values of a variable.逻辑变量我们讨论的双值变量通常叫做逻辑变量，而象或和与这样的操作被称为逻辑操作。现在我们将简要地讨论一下这些术语之间的关联，并在此过程中，阐明用标示“真”和“假”来识别一个变量的可能值的特殊用途。 The circuit of Fig.1-3A-1, showing a pair of cross-coupled NOR gates, is called a flip-flop, It has a pair of input terminals S and R, standing for set and reset ,respectively. We shall use these symbols S and R not only to designate the terminals but also to specify the logical level at the terminals. Thus ,S=1 indicates that a voltage corresponding to logic level 1 is normally present at terminal S . Similarly ,the output terminals and the corresponding output logic levels are Q and Q. In this notation we have explicitly taken account of the fact that in normal operation, as we shall see, the logic levels at the outputs are complementary.图1-3A-1给出的一对交叉连接的或非门电路被称为触发器。其有一对输入端S 和R ，分别代表“置位”和“复位”。我们不仅用符号S 和R 标明端点，而且指定端点的逻辑电平。因此，通常S=1指的是对应于逻辑电平为1的电压出现在S 端。相似的，输出端和相应的输出逻辑电平为Q和非Q。使用这样的符号时，我们已经明确了一个事实，即在我们下面将看到的符号操作中，输出的逻辑电平是互补的。 The types of commercially available DC motors basically fall into four categories:(1) permanent-magnet DC motors, (2) series-wound DC motors, (3) shunt-wound DC motors, and (4) compound-wound DC motors. Each of these motors has different characteristics due to its basic circuit arrangement and physical properties. 现在可以买到的直流电机基本上有四种：永磁直流电机，串励直流电机，并励直流电机，复励直流电机。每种类型的电动机由于其基本电路和物理特性的不同而具有不同的机械特性。The permanent-magnet DC motors ,show in Fig.1-5A-1,is constructed in the same manner as its DC generator counterpart.永磁直流电机，如图1-5A-1所示，是用与直流发电机同样的方法建造的。 The manner in which the armature and filed circuits of a DC motors are connected determines its basic characteristics. 直流电机电枢和激磁电路的连接方式确定了直流电机的基本特性。The word control is usually taken to mean regulate, direct, or command. Control systems abound in our environment. In the most abstract sense it is possible to consider every physical object as a control system.控制一词的含义一般是调节、指导或者命令。控制系统大量存在于我们周围。在最抽象的意义上说，每个物理对象都是一个控制系统。 Control systems designed by hunmans are used to extend their physical capabilities, to compensate for their physical limitations, to relieve them of routine or tedious task,or to save money. 控制系统被人们用来扩展自己的能力，补偿生理上的限制，或把自己从常规、单调的工作中解脱出来，或者用来节省开支。Control theory itself has two categories:classical and modern. Classical control theory, which had its start during World War II, can be characterized by the transfer function concept with analysis and design principally in the Laplace and frequency domains. Modern control theory has arisen with the advent of high-speed digital computers and can be characterized by the state variable concept with emphasis on matrix algebra and with analysis and design principally in the time domain. As might be expected, each approach has its advantages and disadvantages as well as its proponents and detractors.控制理论本身分成两个部分：经典和现代。经典控制理论始于二次大战以传递函数的概念为特征，分析和设计主要在拉普拉斯域和频域内进行。现代控制理论是随着高速数字计算机的出现而发展起来的。它以状态变量的概念为特征，重点在于矩阵代数，分析和设计主要在时域。每种方法都有其优点和缺点，也各有其倡导者和反对者。Open-loop and closed-loop control systems (see Fig.2-1A-1). An open-loop system is one in which the control action is independent of the output. A closed-loop system, however, the input of the plant is somehow dependent on the actual output.开环和闭环系统（如图2-1A-1）：开环控制系统是控制行为与输出无关的系统。而闭环系统，其被控对象的输入在某种程度上依赖于实际的输出。The stability of a continuous or discrete-time system is determined by its response to inputs or disturbance. Intuitively, a stable system is one that remains at rest (or in equilibrium) unless excited by an external source and returns to rest if all excitations are removed. 连续或离散系统的稳定性由其对输入或者干扰的响应决定。直观地说，如果一个系统是稳定的，则其停留在稳态（或者平衡点），除非是受到外部激励，且当外部激励去除后，输出又回到稳态点。The characteristic equation is formed by setting the denominator polynomial equal to zero.将分母多项式等于零即得到特征方程So,a necessary and sufficient condition for the system to be stable is that the roots of the characteristic equation have negative real parts.this ensures that the impulse response will decay exponentially with time. 因此，系统稳定的充分必要条件就是特征方程根的实部为负。这保证脉冲响应将按指数形式随时间衰减。The Routh criterion:All the roots of the characteristic equation have negative real parts if and only if the elements of the first column of the Routh table have the same sign. Otherwise, the number of roots with positive real parts is equal to the number of changes of sign.劳斯判据：当且仅当劳斯表第一行元素有相同的符号时，特征方程的根具有负实数。反之，具有正式部的特征根的个数等于劳斯表第一列元素变号次数。For