《自动化仪表与过程控制》课程学习资料：Introduction

Introduction 2022-2-11

2022-2-11 1 Introduction

Introduction In recent years, automatic control systems have assumed an increasingly important role in the development and advancement of modern civilization and technology Domestically, automatic controls in heating and air conditioning systems. Industrially, automatic control systems are found in numerous applications, such as quality control of manufactured products, machine tool control modern space technology and weapon systems. Even such problems as inventory control social and economic systems control and environment and hydrological systems control may be approached from the theory of automatic control 2022-2-11 2

2022-2-11 2 1.1 Introduction In recent years, automatic control systems have assumed an increasingly important role in the development and advancement of modern civilization and technology. Domestically, automatic controls in heating and air conditioning systems. Industrially, automatic control systems are found in numerous applications ,such as quality control of manufactured products ,machine tool control ,modern space technology and weapon systems .Even such problems as inventory control ,social and economic systems control ,and environment and hydrological systems control may be approached from the theory of automatic control

An example o The human being is a feedback control system, let us consider that the objective is to reach for an object on a desk as one is reaching for the object, the brain sends out a signal to the arm to perform the task The eyes serve as a sencing device which feed back continuously the position of the hand The distance between the hand and the object is the error, which is eventually brought to zero as the hand reaches the object. This is a typical example of closed-loop control 2022-2-11

2022-2-11 3 An example ¨ The human being is a feedback control system ,let us consider that the objective is to reach for an object on a desk ,As one is reaching for the object ,the brain sends out a signal to the arm to perform the task .The eyes serve as a sencing device which feed back continuously the position of the hand .The distance between the hand and the object is the error ,which is eventually brought to zero as the hand reaches the object .This is a typical example of closed-loop control

Types of control system Control systems are classified in terms that described either the system itself or its variables These descriptive terms are mainly of the either-or form 1 An open-loop system is shown in Fig1-1-la and is characterized by the input entering directly into the control elements unaffected by the output the output is related to the input solely by the characteristics of the plant and control elements. In the closed-loop system of Fig 1-1 2b, however the input is modified by the actual output before entering the control elements 2022-2-11 4

2022-2-11 4 Types of control system Control systems are classified in terms that described either the system itself or its variables. These descriptive terms are mainly of the either-or form. 1 An open-loop system is shown in Fig1-1-1a and is characterized by the input entering directly into the control elements unaffected by the output ;the output is related to the input solely by the characteristics of the plant and control elements .In the closed-loop system of Fig.1-1- 2b,however the input is modified by the actual output before entering the control elements

Input output control plant elements Figl-I-la input Control itput elements elements Fig1-1-1b 2022-2-11 5

2022-2-11 5 control elements plant input output Fig1-1-1a Control elements Feedback elements plant input output Fig1-1-1b

2 Lumped parameter system are those for which the hysical characteristics are assumed to be concentrated in one or more,and thus independent of any special distribution For example springs are massless and electrical leads resistanceless 3 A stationary or time-invariant system is one whose parameters do not vary with time 4 A single-variable system is defined as one with only one output for one reference or command input(siso) 5 A multivariable(MIMO)system has any number of inputs and outputs A continuous-variable system is one for which all the system variables are continuous functions of time 2022-2-11 6

2022-2-11 6 2 Lumped parameter system are those for which the physical characteristics are assumed to be concentrated in one or more “lumps” and thus independent of any special distribution .For example springs are massless and electrical leads resistanceless. 3 A stationary or time-invariant system is one whose parameters do not vary with time. 4 A single-variable system is defined as one with only one output for one reference or command input (SISO) 5 A multivariable (MIMO)system has any number of inputs and outputs. 6 A continuous-variable system is one for which all the system variables are continuous functions of time