自动化专业英语 翻译

1.1

In recent years the performance requirements for process plant have become increasingly difficult to satisfy. Stronger competition, tougher (更加严苛的) environmental and safety regulations (法规), and rapidly changing economic conditions have been key factors in the tightening of plant product quality specifications (产品质量规范).A further complication (复杂) is that modern processes have become more difficult to operate because of the trend toward larger, more highly integrated plants with smaller surge capacities (谐振能力) between the various processing units. Such plants give the operators little opportunity to prevent upsets (扰乱) from propagating from one unit to other interconnected units. In view of (考虑到，由于) the increased emphasis placed on safe, efficient plant operation, it is only natural that the subject of process control has become increasingly important in recent years. In fact, without process control it would not be possible to operate most modern processes safely and profitably (有利的), while satisfying plant quality standards.

近年来，对过程系统的性能改善需求变得越来越困难. 更为激烈的竞争，更加严格的环境和安全规范，以及快速变化的经济条件都是加强工厂产品质量规范的关键因素更为复杂的情况是，由于现代制造业朝着规模更大,集成度更高的方向发展,而使不同的加工环节之间的应变能力更低, 所以加工过程更难控制近年来，考虑到工业制造逐渐加强的安全、高效需求，过程控制这个课题变得越来越受重视. 实际上，对于大多数现代工业，要满足安全、高效，产品质量的要求，没有控制系统是不可能的.

It is assumed that the inlet and outlet flow rates are identical (相同的) and that the liquid density ρ (rho) remains consant, that is, the temperature variations are small enough that the temperature dependence of ρ can be neglected. Under these conditions the volume V of liquid in the tank remains constant.

假设输入和输出流量是相等的，并且液体密度保持恒定，也就是说温度变化足够小，密度对温度的影响可以忽略不计. 在这些条件下，槽内液体的体积保持恒定

Use a larger tank. If a larger tank is used, fluctuations (波动) in Ti will tend to be damped out (阻尼，衰减) due to the larger thermal capacitance of the tank contents. However, increased volume of tankage would be an expensive solution for an industrial plant due to the increased capital costs of the larger tank.Note that this approach is analogous to the use of water baths in chemistry laboratories where the large thermal capacitance of the bath serves as a heat sink (散热装置) and thus provides an isothermal (恒温的) environment for a small-scale research apparatus (仪器). 使用一个更大的槽. 如果使用更大的槽，因为更大的热容，Ti的波动会趋向于衰减. 然而，体积增加使得开支增加，会使工厂系统的解决方案变得更加昂贵.要指出的是这个方法类似于化学实验室中水缸的使用，水缸的大热容量可以看作散热装置，因此可以为小型研究仪器提供一个恒温环境.

Note that in feedforward control, the controlled variable T is not measured. 在前馈控制中，被控变量T是没有被测量的. 1.2

The motivation of using feedback, illustrated (说明) by the examples in Section (1), is somewhat oversimplified.In these examples, the use of feedback is shown to be for the purpose of reducing the error between the reference input and the system output.However, the significance of the

effects of feedback in control systems is more complex than is demonstrated by these simple examples.The reduction of system error is merely (仅仅) one of the many important effects that feedback may have upon a system. We show in the following sections that feedback also has effects on such system performance characteristics as stability (稳定性), bandwidth (带宽), overall gain (总增益), disturbance (扰动), and sensitivity (灵敏度).

第一节事例中，应用反馈的动机有些过于简单。在这些例子中，应用反馈的目的是减小参考输入和系统输出间的误差。然而，在控制系统中应用反馈的重要性要比这些简单例子所示的复杂得多. 减少系统误差只是反馈对系统产生的重要作用之一. 在下面的章节里，反馈还能对系统的下列运行特性产生影响：稳定性，带宽，总增益，扰动和灵敏度。

In a practical control system, G and H are functions of frequency, so the magnitude of 1+GH may be greater than 1 in one frequency range but less than 1 in another.Therefore, feedback could increase the system gain in one frequency range but decrease it in another.

在实际的控制系统中，G和H都是频率的函数，因此1+GH的幅值在一种频段下可能增大系统的增益，而在另一频段下又可能减小系统的增益。所以，反馈在一种频段下有可能会加大系统的增益，而在其它频段下减小系统的增益。

It can be demonstrated that one of the advantages of incorporating (包含) feedback is that it can stabilize an unstable system.

可以证明，加入反馈的好处之一是能够使不稳定的系统稳定。 1.3

An important consequence of feedback control is that it can cause oscillatory responses (振荡响应). If the oscillation has a small amplitude and damps out (衰减) quickly, then the control system performance is generally considered to be satisfactory.However, under certain circumstances the oscillations may be undamped (无衰减的) or even have an amplitude that increases with time until a physical limit is reached, such as a control valve being fully open or completely shut. In these situations, the closed-loop system is said to be unstable. 反馈控制的一个重要的结果是会产生振荡响应。如果振荡的幅值很小并且衰减很快，那么一般认为控制系统的运行状态是令人满意的。反馈控制的一个重要的结果是会产生振荡响应。如果振荡的幅值很小并且衰减很快，那么一般认为控制系统的运行状态是令人满意的。然而，在某些情况下，振荡有可能是无阻尼的，甚至幅值会随时间而增大，直到达到了物理极限，比如一个被完全打开或关闭的控制阀。在这些情况下，闭环系统是不稳定的.

Before presenting various stability criteria, we introduce the following definition for unconstrained linear systems (无约束线性系统). We use the term \ideal situation where there are no physical limits on the output variable.

在介绍各种稳定性判据之前，我们先介绍关于无约束线性系统的定义。我们使用术语“无约束”，来特指对输出变量无任何物理约束的理想状况。

Definition of stability. An unconstrained linear system is said to be stable if the output response is bounded (有界的) for all bounded inputs. Otherwise it is said to be unstable.

稳定性的定义：对于一个无约束线性系统，如果对所有的有界输入，输出响应你个都是有界的，那么该系统是稳定的，否则就是不稳定的。

General Stability Criterion. The feedback control system in Fig. 1.3.1 is stable if and only if all roots of the characteristic equation are negative or have negative real parts. Otherwise, the system is unstable.

通用稳定性判据：图1.3.1所示的反馈控制系统是稳定的，当且仅当所有的特征方程的根都是负的或其实部是负的。否则，系统是不稳定的。

Routh Stability Criterion. A necessary and sufficient condition for all roots of the characteristic equation in Eq. (12) to have negative real parts is that all of the elements in left column of the Routh array are positive.

（12）特征方程的所有根均具有负实部的充要条件是，劳思阵的左列的所有元素均为正值。

1.4

Good design eludes (避免) definition (好的设计很难定义), but you can usually recognize something that is well designed. One characteristic of good design is that it is exactly right for the specific application.Everything necessary is present, but everything unnecessary is absent.

好的设计”很难定义，但通常你可以遇见一些好的设计。好的设计的一个特征是，它恰好适用于特定的场合。包括所有需要的，而排除一切所不需要的。 “

The skills needed for good design entail (需要) experience, intuition (直觉), and esthetic (感觉的) sensibility. They are not easily learned from books. The most you ought to expect from any textbook on design (including this one) is to learn about some useful tools.

好的设计所需要的技巧包括经验、直觉和敏锐的感觉。这些从课本中并不容易学到。在设计方面，你最应该从教科书中期望得到的是学到一些有用的工具。

In practice one learns that most systems develop through evolution: not only biological systems, but also human inventions such as the automobile and the airplane. The sleek (豪华的), high-performance automobile can be traced to (上溯到) the humble (粗陋的) model T; the advanced tactical fighter, still on the contractors (承包商) drawing boards, has its roots at Kitty Hawk (基蒂霍克：即莱特兄弟首次两个成功飞行的地点 1903年12月17日).

实际上，大多数系统都通过进化发展的，不仅是生物系统，人类的发明，如汽车和飞机也是这样。豪华而高性能的汽车可以追溯到简单的T模型；最先进的，甚至只出现在承包商的画板上的战斗机， 也是起源于老式的“小鹰”飞机。

First you need a physical appreciation (判断) of the problem by determining the physical quantity or quantities that must be controlled, and the level of performance required.

首先，你需要通过确定要控制事物的质量或数量，以及所需要的性能级别来正确评价问题

After satisfying yourself that you understand the technical and non-technical issues, you make a tentative (实验性的，尝试的) selection of appropriate hardware. Only after the hardware is selected does the analytic phase of the design process begin. 当你感到自己对技术和非技术方面充分理解之后，你会尝试选择合适的硬件。只有选择完硬件之后，设计过程的分析阶段才可以开始

The first step is to select an appropriate design methodology.(Here a knowledge of the methods

discussed in this book would be helpful.) Concurrently (同时) you might begin developing a \— a set of differential and algebraic equations that you are confident adequately represents the behavior of the process. The truth model, which can be used in a simulation for evaluating the performance of the design, is usually too complicated for design purposes. Hence you will probably want to develop a “design model” by simplifying the truth model.

第一步是选择合适的设计方法（这里，本书中讨论的方法知识是很有帮助的）. 同时，你也许要着手建立动态过程的“真实模型”－你确信足以表达过程行为的一系列微分和代数方程。 真实模型可以被用于仿真来评估设计性能，但它通常对设计目标来说过于复杂。因此，你将很有可能希望通过简化真实模型来建立一个“设计模型”。

Having adopted a design methodology and developed a design model, you proceed to perform the design calculations.

采用某种设计方法，并建立了设计模型之后，该进行设计计算了。

The final step in the analytical phase of the design is to evaluate the performance of the system by means of a simulation based on the truth model.

分析过程的最后一步是通过对基于真实模型的仿真来验证（评估）系统的运行性能。

In principle, the flight control problem could be formulated as a general optimization problem: 原则上，飞行控制问题可以被表述成一个通用的优化问题 1.5

After a control system is installed the controller settings must usually be adjusted until the control system performance is considered to be satisfactory. This activity is referred to as controller tuning or field tuning of the controller. Because controller tuning is usually done by trial and error (试差法), it can be quite tedious (费时的) and time-consuming. Consequently, it is desirable to have good preliminary (初步的) estimates of satisfactory controller settings.A good first guess may be available from experience with similar control loops.Alternatively, if a process model or frequency response data are available, some special design methods can be employed to calculate controller settings. However, field tuning may still be required to fine tune the controller, especially if the available process information is incomplete or not very accurate.

当安装了控制系统之后，通常必须先调整控制器的设置，直到控制系统运行达到满意为止。这个活动被称为控制器整定，或控制器的现场整定。由于控制器整定通常都采用反复实验的方法（试差法），整定过程是十分费时的。因此，我们希望能够初步估计出一个令人满意的控制器设置。首先好的设想可以源于类似控制回路中取得的经验。换句话说，如果已知过程模型或频率响应数据，就可以采用一些特殊的设计方法来计算控制器设置。然而，现场整定仍是控制器微调所需要的，尤其是当过程信息不完整或不太准确的时候.

Flow and liquid pressure control loops are characterized by fast responses (on the order of seconds), with essentially no time delays (没有时间延迟). The process dynamics are due to compressibility (in a gas stream) (气体可压缩性) or inertial effects (in a liquid) (液体惯性). The sensor and signal transmission line may introduce significant dynamic lags (滞后) if pneumatic instruments are used. Disturbances in flow-control systems tend to be frequent but generally not of large magnitude. Most of the disturbances are high-frequency noise (periodic or random) due to

stream turbulence (湍流), valve changes, and pump vibration (泵的振动). PI flow controllers are generally used with intermediate values of the controller gain Kc. The presence of recurring (重复) high-frequency noise rules out (排除在外) the use of derivative action. 流量和液压控制回路的特点是响应快速（秒级），基本上没有时间延迟。过程的动态特性是由于气流的可压缩性或液体的惯性造成的。传感器和信号传输线如果采用气动设备，有可能会带来很大的动态滞后（延迟）。流量控制系统中的扰动较为频繁但通常幅值较小。多数扰动是高频噪声（周期性或随机性），来源于流体紊乱、阀门变化和泵的振动. 通常使用PI流量控制器，控制器增益Kc取中间值。而不断重复的高频噪声使得微分作用无法使用.

Controller field tuning is often performed using trial and error procedures suggested by controller manufacturers. A typical approach for PID controllers can be summarized as follows: 控制器的现场整定经常根据控制器生产厂家的要求，采用经验试凑法

Step 3. Increase the controller gain Kc by small-increments (增加) until continuous cycling (循环，这里指振等幅连续) occurs after a small set-point or load change. The term “continuous cycling\

第3步：使设定值或负载变化较小的量，逐步增加控制器增益Kc，直到等幅连续循环出现. 术语“连续循环”指的是等幅振荡

Continuous Cycling Method等幅振荡法 Process Reaction Curve Method过程响应曲线法

These tuning relations have been widely used in industry and serve as a convenient base case for comparing alternative control schemes. However, controller tuning examples presented later in this section indicate that Z-N tuning can be inferior to settings obtained by other methods and should be used with caution.

这些整定关系在工业中得到了广泛的应用，也为比较不同的控制方案提供一个方便的基础。然而，本节将要讲述的控制器整定例子表明，Z-N整定要次于其它方法，应该谨慎使用。 2.1

Atmosphere pressure is the presence on the earth’s surface due to weight of the gases in the earth’s atmosphere and is normally expressed at sea level as 14.7 psi or 101.36 kPa. It is however, dependant on atmospheric conditions. The pressure decreases above sea level and at an elevation (上升) of 5000 ft drops to about 12.2 psi (84.122 kPa).

大气压指空气由于自身重力作用于地球表面的压力，通常表示为海平面大气压，14.7 psi 或 101.36 kPa. 但是，它取决于空气条件. 海平面之上压力降低，在海拔上升到5000英尺下，压力降低到大约12.2 psi (84.122 kPa).

Absolute pressure is the pressure measured with respect to (相对于) a vacuum and is expressed in pounds per square inch absolute (psia).

绝对压是相对于真空压测量到的压力，表示为磅每平方英尺 (psia).

Gauges are a major group of pressure sensors that measure pressure with respect to atmospheric pressure. 量表是一类主要的压力传感器，测量相对于大气压的压力.

A diaphragm consists of a thin layer or film (膜) of a material supported on a rigid frame and is

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