《电气工程英语》课程教学资源（课文）U4 Automatic Control.pdf_大学文库

Text A Automatic Control Automatic control in engineering and The history of automatic control traces technology is a wide generic term covering back to Ancient Greece.It was a the application of mechanisms to the preoccupation of the Greeks and Arabs operation and regulation of processes (in the period between about 300 B.C. without continuous direct human and about 1200 A.D.)to keep accurate intervention. track of time.In about 270 B.C.the Greek Ctesibius invented a float for a water 2 Automatic control covers the range of clock,a device not unlike the ball and cock application from a household thermostat in a modern flush toilet.The invention of controlling a boiler,to a large industrial the mechanical clock in the 14th century control system with tens of thousands of made the water clock and its feedback input measurements and output control control system obsolete.The float regulator signals.In control complexity it can range does not appear again until its use in the from simple on-off control to multi- Industrial Revolution variable high level algorithms. s Thomas Newcomen invented the steam In the simplest type of an automatic engine in 1713,and this date marks the control loop,a controller compares a accepted beginning of the Industrial measured value of a process with a desired Revolution.However,its roots can be set value,and processes the resulting error traced back into the 17th century.The signal to change some input to the process, introduction of prime movers,or self- in such a way that the process stays at its driven machines advanced grain mills set point despite disturbances.This closed- furnaces,boilers,and the steam engine loop control is an application of negative created a new requirement for automatic feedback to a system.The mathematical control systems including temperature basis of control theory was begun in the regulators(invented in 1624),pressure 18th century,and advanced rapidly in the regulators(1681).float regulators (1700) 20th century. and speed control devices.The design of Unit 4 Automatic Control 67

Automatic Control ,, , 1 Automatic control in engineering and technology is a wide generic term covering the application of mechanisms to the operation and re lation of processes without continuous direct human 1 intervention . 2 Automatic control covers the range of application from a household thermostat con oiling a boiler, to a large industrial control system with tens of thousands of input measurements and output control signals. In con ol complexity it can range from simple on-off con ol to multivariable high level algorit 3 In the simplest type of an automatic control loop, a controller compares a measured value of a process with a desired set value, and processes the resulting error signal to change some input to the process, in such a way that the process stays at its set point despite disturbances. This closedloop control is an application of negative feedback to a system. The mathematical basis of control theory was begun in the 18th century, and advanced rapidly in the 20th century. - 4 The history of automatic control traces back to Ancient Greece. It was a preoccupation of the Greeks and Arabs (in the period between about 300 B.C. and about 1200 A.O.) to keep accurate track of time . In about 270 B.C. the Greek Ctesibius invented a float for a water clock, a device not unlike the ball and cock in a modem flush toilet. The invention of the mechanical clock in the 14th century made the water clock and its feedback control system obsolete. The float regulator does not appear again until its use in the Industrial Revolution. s Thomas Newcomen invented the steam engine in 1713, and this date marks the accepted beginning of the Industrial Revolution. However, its roots can be traced back into the 17th century. The introduction of prime movers, or selfdriven machines advanced grain mills, furnaces, boilers, and the steam engine created a new requirement for automatic control systems including temperature regulators (invented in 1624), pressure regulators (1681), float regulators (1700) and speed control devices. The design of Unit 4 Automatic Control 6 7

feedback control systems up through the s Fundamentally,there are two types of Industrial Revolution was done by trial- control loop:open loop control and closed and-error,together with a great deal of loop control. engineering intuition.Thus,it was mor of an art than a science.In the mid-19th In open loop control,the control action century mathematics was first used to from the controller is independent of the analyze the stability of feedback control process output.A good example of this is a systems.Since mathematics is the formal central heating boiler controlled only by a language of automatic control theory,we timer,so that heat is applied for a constant could call the period before this time the time,regardless of the temperature of the prehistory of control theory. building. The First and Second World Wars saw 10 In closed loop control,the control action major advancements in the field of mass from the controller is dependent on the communication and signal processing. process output.In the case of the boiler Other key advances in automatic control analogy this would include a thermostat include differential equations,stability to monitor the building temperature, theory and system theory,frequency and thereby feed back a signal to ensure domain analysis,ship control,and the controller maintains the building at stochastic analysis. the temperature set on the thermostat. A closed loop controller therefore has a With the advent of the space age in 1957 feedback loop which ensures the controller controls design,particularly in the United exerts a control action to give a process States,turned away from the frequency- output the same as the"reference input" domain techniques of classical control or“set point'”.For this reason,closed theory and backed into the differential loop controllers are also called feedback equation techniques of the late 19th century. controllers. which were couched in the time domain. The modern era saw time-domain design The definition of a closed loop control for nonlinear systems,navigation,optima system according to the British Standard control and estimation theory,nonlinear Institution is"a control system possessing control theory,digital control and filtering monitoring feedback,the deviation signal theory,and the personal computer. formed as a result of this feedback being 68电气工程英语

feedback control systems up through the Industrial Revolution was done by trial- . and-error, together with a great deal of engineering intuition. Thus, it was more of an art than a science. In the mid-19th century mathematics was first used to analyze the stability offeedback control systems. Since mathematics is the formal language of automatic control theory, we could call the period before this time the prehistory of control theory. 6 The First and Second World Wars saw major advancements in the field of mass communication and signal processing. Other key advances in automatic control include differential equations, stability theory and system theory, frequency domain analysis, ship control, and stochastic analysis. 1 With the advent of the space age in 1957, controls design, particularly in the United States, turned away from the frequencydomain techniques of classical control theory and backed into the differential 68 equation techniques of the late 19th centu which were couched in the time domain. The modem era saw time-domain design for nonlinear systems, navigation, optimal control and estimation theory, nonlinear control ory, digital control and filtering theory, and the personal computer. 电气工程英语 s Fundamentally, there are two types of control loop: open loop contI·ol and closed loop control. 9 In open loop control, the control action from the controller is independent of the process output. A good example of this is a central heating boiler controlled only by a _ timer, so that heat is applied for a constant time, regardless of the temperature of the building. 10 In closed loop control, the control action from the controller is dependent on the process output. In the case of the boiler analogy this would include a thermostat to monitor the building temperature, and thereby feed back a signal to ensure the controller maintains the building at the temperature set on the thermostat. A closed loop controller therefore has a feedback loop which ensures the controller exerts a control action to give a process output the same as the "reference input" or "set point". For this reason, closed loop controllers are also called feedback controllers. 11 The definition of a closed loop control system according to the British Standard Institution is "a control system possessing monitoring feedback, the deviation signal formed as a result of this feedback being