【文章內容簡介】 ntrol systems may possibly contain devices which could be defined as servomechanisms .The following are examples of control problems usually classified as process control。然而一個復雜的過程控制系統(tǒng)可能包含好幾個被稱作伺服機構的裝置。11：Its standard range is from 4 to 20mA DC for the current signal or from 1 to 5V DC for the voltage signal .其標準范圍對電流來說是420mA DC,對電壓力信號來說是15V DC。M: 1：Measurement must be made to indicate the current value of the variable controller by the loop . 必須具有測量環(huán)節(jié)，以指示被測回路所控制的變量當前值。//Common measurement used in industry include flow rate, pressure , level, temperature ,analytical measurement (such as pH ,ORP and conductivity ),and many others particular to special ，壓力，物位，溫度，分析測量參數，如PH值，ORP 和電導率 ，以及許多其他特殊工業(yè)中的特殊參數。2: More precisely ,it is approximately proportional to the product of the field density and the current ,some nonlinearity being introduced by the distortion of the stator field due to the flux generated by the armature current .This socalled “armature reaction” is kept small by carefully motor design .更確切的說,轉矩接近正比于場強與電流的乘積。電樞電流產生的磁通使定子磁場畸變，所以產生了某些非線性，這叫做“電樞反應”。在經周密設計的典籍中，這種電樞反應可以很小。3：Most classical control techniques were developed for linear constant coefficient systems with one input and one output (perhaps a few input and outputs) .大多數經典控制技術都是帶有一個輸入、一個輸出（也可有數個輸入和輸出）的線性、常系數系統(tǒng)而發(fā)展起來的。//The language of classical techniques is the Laplace or ztransform and transfer function . 經典技術的表達語言室拉普拉斯或者z變換以及傳遞函數。//When nonlinearities and time variations are present ,the very basic for these classical techniques is removed .一旦出現(xiàn)非線性和時變性，經典技術最根本的基礎就不復存在了。//Some successful techniques such as phaseplane methods ,describing functions ,and other ad hoc methods ,have been developed to alleviate this shorting . 諸如相平面方法、描述函數法和其它有關方法這樣一些很成功的技術能夠得以發(fā)展的原因就是為了彌補這一短處。//However ,the greatest success has been limited to loworder systems . 然而經典控制理論的最大成功也是局限于低階系統(tǒng)中。//The state variable approach of modern control theory provides a uniform and powervarying or constant coefficients . 現(xiàn)代控制理論的狀態(tài)變量法提供了一種統(tǒng)一、高效的方法來描述具有任意階次、線性或非線性、時變或常系數的各種系統(tǒng)。//It provides an ideal formulation for puter implementation and is responsible for much of the progress in optimization theory .它也為計算機處理提供了一種理想的表示方法，并引起了許多方面最優(yōu)化理論的進展。4：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 。因此，對線性電路性能和線性電路分析的研究就具有理論和實踐的雙重意義。N: 1:Negative feedback also increases the frequency bandwidth of the amplifier to which it is applied , because the gainbandwidth product of a linear amplifier is a constant , and negative feedback reduces the effective gain. 由于線性放大器的增益帶寬積是個常數，而負反饋的運用減小了有效增益，因此，負反饋還能拓寬運用了負反饋的放大器的頻帶寬度。2: Negative feedback occurs when a portion of the output signal of an amplifier is fed back and subtracted from the input signal, causing a reduction in the effective input signal. 所謂負反饋是指輸出信號的一部分被送回輸入端，與輸入信號相減，從而削弱了有效輸入信號，//The most important effect of this is to make the overall amplifier gain almost immune to changes in the amplifier unit gain, and dependent almost entirely on the feedback network ，其總增益的大小完全取決于反饋網絡的元件參數。3: Now ,another type of electrical signal ,which is being mon , is the digital or discrete signal .當今，另一種電信號形式變得越來越常用，就是數字或者是離散信號。O: 1：One additional distinction not shown in could be made between largescale system and smallscale system . 。//The degree of difficulty in analysis varies greatly among these system classification . 不同系統(tǒng)類型，對其進行分析難度相差很大。 //These differences have motivated different methods of approach . 這些差別已經促進了不同的方法的發(fā)展。//Modern control theory provides one of the most general approaches .現(xiàn)代控制理論提供了一種最一般性的方法。2：One of the conductors is mon to both sides of the bridge while the other two connect one to each side of the bridge . 三導線中，其中一根對電橋兩臂是相同的，而其它兩根連在電橋的兩臂上。//Any change in cable temperature will be cancelled as both sides of the bridge are changed a like amount .由于兩橋臂的變化是一樣的，所以電纜上的任何溫度變化就會被抵消。3：Operational amplifiers with very high gains are readily available , making the application of negative feedback on a large scale practical and inexpensive. 高增益的運算放大器是容易得到的，這便使負反饋的使用現(xiàn)實而經濟。4：Output interface take a similar form () ,the obvious difference being that here the flow of information is in the opposite direction. it is passed from the program to the outside world .輸出接口采用相似的形式（）,明顯的差別在于信息流的方向相反，是從程序到外部世界。S: 1：Several factors provided the stimulus for the development of modern control theory :(1)The necessity of dealing with more realistic models of systems .(2)The shift in emphasis towards optimal control and optimal system design .(3)The continuing developments in digital put