外文翻譯---自動(dòng)控制基礎(chǔ)

1、<p>　　附錄 英文資料及其譯文</p><p>　　CHAPTER 1 Basis of the automatic control</p><p>　　1.       Out line </p><p>　　This device is temperature control expe

2、rimental device of temperature, lever, pressure , that are the most common control subject for water treatment plants, chemical factories and power plants. </p><p>　　At the experiment of automatic control,

3、it is very important to keep the balance of system. Automatic control system is composed of control subjects and to keep control device. Especially process control has many control subjects to keep self-balance, so the e

4、xperimental results is conducted with balance condition.</p><p>　　This experimental device experiments about the relation of input signal and output signal to keep the balance (System characteristics) at the

5、 cascade experiment and fixed command control, also experiments on dynamic characteristic (Balance condition without time variation),static characteristic (Balance condition considerating time variation).</p><

6、p>　　And you record the change of control amount which was input handling amount or establishment of characteristic experiment. These typical response can be thought step response . You experiment optimum control exper

7、iment , fixing P . I. D constant of control device</p><p>　　, relating this step response.</p><p>　　2.       Process control </p><p>　　Process control

8、keeps the balance of the system, automatically correcting toward deviation, and compares every variable to operating toward deviation, and compares every variable to operation condition of industrial process of flux, tem

9、perature, surface, pressure, etc with the established goal.</p><p>　　Process control is decided into closed loop and Open loop control.</p><p>　　3.       Kinds of a

10、utomatic control </p><p>　　Control is composed of detection (measurement), comparison, judgment, operation and manual control is done by man’s hand and automatic control is done by measure or adjuster or oth

11、er machinery.</p><p>　　At present, automatic control is taken at the many plants . Moreover , we cannot think plant control without automatic control.</p><p>　　Kinds of automatic control is deci

12、ded like below.</p><p>　　Automatic control Open loop control Feed forward control </p><p>　　Sequential control</p><p>　　Closed loop controlFeedback control<

13、;/p><p>　　3-1 . Feed back control </p><p>　　Feed back control detects (measure) compares , judges ,operates ,automatically. And it measures the results every moment , and corrects automatically if

14、 there is any differential between the desired value (set value).</p><p>　　Feed back control is one of the main process control . </p><p>　　This is the control that detecting (measuring) the re

15、sults (Control amount: tank water lever ) with differential transmitter, and comparing the value with the set water lever and correct the deviation(Opening operation flow control of the control value)</p><

16、p>　　Like the above, feed back control automatically does the movement of measurement(detection) comparison calculation modernfication. Feed back system has the element of doing these functions.</p><p>　　A

17、t the diagram 3-1 block line diagram it is the closed loop and it transmitted the correcting signal of the opposition toward the process flow.</p><p>　　Block line diagram: Indicating the constructing element

18、 of control system in block , and connecting the line expressing the signal flow.</p><p>　　Signal :The amount being used for transmit the information</p><p>　　3-2.Feed forward control</p>

19、<p>　　Feed forward control is the control method doing necessary correct movement before the influence appears to the control system , when disturbance enters into the control system.</p><p>　　At feed

20、back control, it starts correct movement to erase the deviation after the influence by disturbance appears, so in case of sudden change of disturbance or set value, then control disorders transiently and arises many prob

21、lems.</p><p>　　Feed forward control breaks down this weak point.</p><p>　　At feed forward control, results of the controller is not done feedback and becomes open-loop control, not being close-l

22、oop control. Accordingly, in case of feed back control, the relation between cause and effect of disturbance and the results of control must be understood well. That is ,relation of influence to the control amount toward

23、 load change, and operating amount needed to compensate it should be clear.</p><p>　　But it is generally difficult. In many cases it is difficult that all the disturbance is detected, and to get the perfect

24、process model in actual process.</p><p>　　Moreover it is difficult to avoid constant deviation, so it is used combined with feed back control.</p><p>　　3-3 Sequence control</p><p>　

25、　Sequence control processes the fixed process in advance step by step. This sequence control is used in neon signs, vending machines, or electric washing machines. On the other hand, it is needed in the producing process

26、 at chemical factory, automobile factory, conveyer, automatic warehouse as automation.</p><p>　　3.4       Classification of control methods</p><p>　　Production meth

27、od by continuous process is employed, when scale of process industry gets bigger and larger production amount id requested.</p><p>　　You need to make proper use of the control method on some different condit

28、ion of operation. To classfy automatic control system is difficult strictly because their control system has correlation. But general method of cassification will be like below.</p><p>　　4-1 Classification

29、 by desired value</p><p>　　Automatic control Fixed command control</p><p>　　Following control Follow up control </p><p>　　Program control</p><p>　　4-1-1

30、 Fixed command control</p><p>　　Most of the controls belong to this control when desired value is constant.</p><p>　　4-1-2 Following command control</p><p>　　Servo mechanism compo

31、sed to follow the change belongs to this control when desired value changes optionally.</p><p>　　4-1-3 Program control</p><p>　　It is used for the control in which desired value changes accordi

32、ng to fixed time schedule. Normally , it is well used to temp. Control of fever process of metal or batch process at the chemical industry.</p><p>　　4-2. Classification by control method</p><p>

33、　　Automatic control Unity control loop</p><p>　　Ratio control </p><p>　　Cascade control</p><p>　　4-2-1 ratio control</p><p>　　It is well used to flow control of

34、2 fluid when desired value keeps with other fluid (other amount) constantly.</p><p>　　You compare and measure if special ratio keeps toward basic fluid (B), then maintain the ratio as the purpose.</p>

35、<p>　　4-2-2 Cascade control</p><p>　　It is the control method that more than 2 automatic control systems control by output of other control device. In short, control circuit is combined in series.</

36、p><p>　　You change the desired value of flow by output of flux adjuster. If you control the desired value of flow control to fix water level in water tank, then you can prevent the influence to the level such a

37、s main pressure change of flow itself.</p><p>　　The purpose of cascade control method is to absorb disturbance at first control, also to make easy the next step control, and to progress the control on the wh

38、ole.</p><p>　　3.5      Control action</p><p>　　At control action, movement to reduce control deviation, giving operating amount in accordance with a movement signal

39、 is called control action.</p><p>　　The following is this classification.</p><p>　　5-1 Continuous control</p><p>　　It does constantly correct movement toward deviation with desire

40、d value,measuring continuously toward controlled variable change.</p><p>　　5-1-1 Proportional action</p><p>　　It is the movement that operating amount Y is in proportion to movement signal and

41、deviation.</p><p>　　Suppose you make deviation as e, gain as kp,</p><p>　　3.6       Automatic control apparatus </p><p>　　Following apparatus are nece

42、ssary for each part, like a block diagram( See diagram 3-2) of feedback control. </p><p>　　◇ Primary Detecting element</p><p>　　◇ Final control element</p><p>　　◇ Controlling means&

43、lt;/p><p>　　6-1 Primary Detecting element</p><p>　　This is the part to take out necessary signals from controlling object , and transmit on control devece.</p><p>　　Expanding thermomet

44、er (Bimetal type)</p><p>　　Bimetal is the joined two metal boards which have different thermal expansion coefficient. It curves by temp.change.</p><p>　　Pressure type thermometer ( Vapor pressur

45、e )</p><p>　　You put vaporlizable liquied like propane or ether into thermal sensitivity part.</p><p>　　These liquid has certain vapor pressure, by contact surface with gas, and it deflects the

46、needle, by changing pressure measuring mechanism. </p><p>　　Resistance thermometer </p><p>　　It is well known that in thermometry resistor (Rt). Its resistance increases as electric resistance

47、 changes by temp. and temp. rises.</p><p>　　You build a bridge with thermometry resistor, and when its resistance value changes by temp., unbalanced current generates at the bridge. From this, you will know

48、the temperature. </p><p>　　(4)   Thermoelectric thermometer (Thermocouple)</p><p>　　Zeebesk effect is employed. You connect different kinds of metal. And make one connecting point temp

49、.(Thermometry contact point) higher than another connecting point (Standard contact point) . Then thermoelectromotive force is generated between both connecting points. </p><p>　　(5) Radiant thermometer &l

50、t;/p><p>　　Solid emits radiant energy in proportion to the square of four of absolute temp., like Stefan-Boltzmann’s formula.</p><p>　　(6) Thermocouple and thermometry resistor</p><p>

51、　　Detecting part (Temp.sensor) of temp.control experimental device (SPC-201) is mostly used in industrial tem.measurement.And it employs thermocouple and thermometry resistor with which you can measure in high accuracy a

52、nd easily. </p><p>　　6-2. Final control element ( Control valve)</p><p>　　Control valve receives output of adjuster and converts it into process variable Control valve is the element to feedbac

53、k to the process. So decides valve specifications. Understanding each controlled objects.</p><p>　　6-2-1 Control valve feature</p><p>　　(1) Flow feature( Proper feature)</p><p>　　Re

54、lation of lift of control valve. That is , valve operation signal, with flux is called flow feature,equal percentage feature and on-off feature represent.</p><p>　　near feature</p><p>　　queral

55、percentage feature</p><p>　　3、 On-off feature</p><p>　?、?#160;    Linear feature</p><p>　　Valve opening degree and flow are in proportion. Accordingly, flux changes 1

56、0% linearly,</p><p>　　as opening degree changes 10%.</p><p>　?、?#160;    Equal percentage feature</p><p>　　Flow increasing modulus becomes constant toward unit change

57、 of valve lift . Suppose there is flow increasing modulus at 10%, toward n% change of lift. Then flow will be.</p><p>　　When 10 L/min weighting is 10*0.1=1 L/min</p><p>　　When 50 L/min weighting

58、 is 50*0.1=1 L/min </p><p>　　When 90 L/min weighting is 90*0.1=1 L/min </p><p>　　Even if the same n% lift change, flow change is small, if flow is small. And it becomes big if flow is big. So, i

59、t has fine adjustment feature over wide flow range.</p><p>　?、?On-off feature</p><p>　　Flow soon reaches to the max.value, when a valve shift starts to move. It is usually used for 2-positionin

60、g control.</p><p>　　It is called on-off feature or quick open feature.</p><p>　　Relation of PID value and disturbance and control response toward setting change. Collect the relationship of P

61、ID value and control response toward disturbance, from experimental results, acquired at experiments.</p><p>　　proportional (P) action effect </p><p>　　????????????To increase proportional gain

62、</p><p>　　?To decrease off set amount (In case of no-integral action)</p><p>　　?To become oscillative ,and be hunting condition</p><p>　　?To get shouter the period of oscillation &l

63、t;/p><p>　　Integral (I) action results </p><p>　　Following things are conducted in a experiment ,changed only integral time TI and shortening TI.</p><p>　　?To lose off set amount</p

64、><p>　　?The first mountain gets smaller</p><p>　　?To become oscillative. Amplitude damping ratio gets bigger to finally exhale </p><p>　　?Returning time initially to setting value is s

65、hortened.</p><p>　　Differential (D) action effect </p><p>　　Following thing is conducted in a experiment ,changing only differential time and making TD longer.</p><p>　　?Off set amo

66、unt does not change (In case of no-integral action)</p><p>　　?The first mountain gets smaller</p><p>　　?Oscillation is restrained. Amplitude damping ratio gets smaller. But ,if differential time

67、 is too long ,it becomes oscillative again.</p><p>　　?Oscillaion period is shortened.</p><p>　　8. P.I.D adjustment procedure</p><p>　　You shall understand PID feature and nature fro

68、m experiments you did ,however, have difficulty in finding true value ,despite the adjustment .</p><p>　　Adjust P-I-D in order. Make step change toward desirable value, changing each constant. Then confirm a

69、nd record the results.</p><p>　　Change proportional (P) band from large number to small number. Stop it when measuring value causes hunting.</p><p>　　Change integral time (TI) from large number

70、to small number, too. Stop it when measuring value causes hunting, and bring a little back larger.</p><p>　　Change differential time (TD) from small number to large number. Stop it when measuring value cause

71、s hunting, and bring a little back smaller.</p><p>　　When you wish to shorten setting time, make P much smaller, and check the change of measuring value.</p><p>　　9. Optimum adjustment</p>

72、<p>　　To arrange the control purpose based on the former experiments.</p><p>　　When you change desirable value, make measuring value and desirable value agree, as soon as possible. (Desirable value ch

73、ange, step response)</p><p>　　If measuring value deviates from desirable value, owing to changes of surrounded condition temporarily, put it back as soon as possible. (Disturbance response)</p><p&

74、gt;　　As for (1) , time passage to make them agree is the problem. Measuring value change on PID value, in case of desirable value change, will be normally like diagram 9-1.</p><p>　　At this diagram, temporar

75、ily it gets over desirable value. This is called overshoot. To decrease this over amount, and to shorted time to settle down measuring value (Setting time) do not normally coexist. In short, adjusting not to get over mak

76、es the setting time longer.</p><p>　　Also, control process may have some trouble, if you shorten the setting time, ignoring over amount. On the other hand, it may be better to reach the desirable value soone

77、r in spite of over amount. So, establishing guideline of overshoot, and you have and adjusting method, making time minimum within the range. It is called optimum adjustment, to adjust PID constant.</p><p>&l

78、t;b>　　自動(dòng)控制基礎(chǔ)</b></p><p><b>　　提綱</b></p><p>　　這套設(shè)備是用來(lái)測(cè)量溫度、流量、液位、壓力的實(shí)驗(yàn)設(shè)備中的溫度的設(shè)備。溫度、流量、液位、壓力這些控制量是水處理廠(chǎng)、化工廠(chǎng)、電廠(chǎng)中最普遍的控制對(duì)象。在這些自動(dòng)控制實(shí)驗(yàn)中，最重要的是保持系統(tǒng)平衡。</p><p>　　自動(dòng)控制系統(tǒng)是由控制對(duì)

79、象、控制裝置組成的。尤其是過(guò)程控制，它要求有多種控制對(duì)象來(lái)保持自身平衡。因此，實(shí)驗(yàn)結(jié)果是在平衡的情況下得到的。在串級(jí)實(shí)驗(yàn)和固定命令控制下，這套實(shí)驗(yàn)裝置通過(guò)測(cè)試輸入與輸出的關(guān)系來(lái)保持系統(tǒng)的平衡。因此，這套系統(tǒng)有靜態(tài)特性和動(dòng)態(tài)特性。</p><p>　　這個(gè)反映是階躍響應(yīng)的結(jié)果。</p><p><b>　　過(guò)程控制</b></p><p>　　過(guò)

80、程控制是保持系統(tǒng)的平衡，自動(dòng)調(diào)整偏差。根據(jù)工業(yè)過(guò)程中液面、壓力、流量、溫、等要求的目標(biāo)來(lái)比較，自動(dòng)調(diào)節(jié)偏差。</p><p>　　過(guò)程控制分為開(kāi)環(huán)控制和閉環(huán)控制。</p><p>　　3、 自動(dòng)控制的種類(lèi)</p><p>　　控制是由檢測(cè)裝、比較裝置、調(diào)節(jié)裝置、執(zhí)行裝置組成并且手動(dòng)控制是由人通過(guò)手工實(shí)現(xiàn)的，自動(dòng)控制是通過(guò)機(jī)械、調(diào)節(jié)器、檢測(cè)器實(shí)現(xiàn)的。在目前，自動(dòng)被用于

81、許多工廠(chǎng)中，甚至，我們無(wú)法想象，在工廠(chǎng)中沒(méi)有過(guò)程控制會(huì)怎樣。</p><p>　　各種過(guò)程控制的分類(lèi)如下所示：</p><p><b>　　3-1反饋控制</b></p><p>　　自動(dòng)控制 開(kāi)環(huán)控制 前饋控制</p><p><b&

82、gt;　　順序控制</b></p><p>　　閉環(huán)控制 反饋控制</p><p>　　反饋控制主要依據(jù)比較部分來(lái)實(shí)現(xiàn)自動(dòng)操作。它返回的每部分的測(cè)量結(jié)果，如果測(cè)量值與給定值產(chǎn)生偏差，那么根據(jù)二者之差將操作值也作相應(yīng)的調(diào)整。</p><p>　　反饋控制是一種主要的過(guò)程控制，我們將以如圖3-1的液位控制系統(tǒng)為例進(jìn)行介紹。</

83、p><p>　　這個(gè)控制系統(tǒng)檢測(cè)結(jié)果（被控參數(shù)：水塔的液位）被測(cè)量變送器轉(zhuǎn)化之后，與設(shè)定液位進(jìn)行比較，然后根據(jù)比較結(jié)果閥的開(kāi)度，直至最后使液位達(dá)到平衡。</p><p><b>　　3-2、前饋控制</b></p><p>　　前饋控制特點(diǎn)：按干擾作用的大小進(jìn)行控制，可以克服擾動(dòng)或給定突然改變帶來(lái)的問(wèn)題，一般比反饋控制要及時(shí)，但一種前饋控制只能克服

84、一種干擾；反饋控制屬于閉環(huán)而前饋控制屬于開(kāi)環(huán)控制，且其使用的是視對(duì)象特性而定的特殊控制器。</p><p>　　一般前饋控制很難達(dá)到控制要求，因?yàn)閷?duì)實(shí)際系統(tǒng)來(lái)說(shuō)將所有的擾動(dòng)區(qū)分開(kāi)來(lái)去建立一個(gè)實(shí)際模型是不可能的。因此，前饋控制通常與反饋控制、串級(jí)控制共同使用以達(dá)到良好的控制效果。</p><p><b>　　3-3、順序控制</b></p><p&g

85、t;　　順序控制適用于高級(jí)單步執(zhí)行系統(tǒng)。這種順序控制常用在霓虹燈廣告牌，全自動(dòng)洗衣機(jī)或電動(dòng)洗衣機(jī)等領(lǐng)域，另一方面，化工廠(chǎng)、汽車(chē)廠(chǎng)、轉(zhuǎn)化器、自動(dòng)倉(cāng)庫(kù)的生產(chǎn)過(guò)程中也經(jīng)常使用順序控制器。</p><p><b>　　4、控制方法的分類(lèi)</b></p><p>　　實(shí)際和產(chǎn)經(jīng)常使用連續(xù)的生產(chǎn)方式，而生產(chǎn)過(guò)程中很少有要求太大的被控量。</p><p>　

86、　4-1 根據(jù)給定值分類(lèi)</p><p>　　自動(dòng)控制： 定值控制</p><p><b>　　隨動(dòng)控制：隨動(dòng)控制</b></p><p><b>　　程序控制</b></p><p>　　4-1-1 恒值控制</p><p>　　實(shí)際生產(chǎn)中，大多數(shù)的控制都屬于給定值為常數(shù)的

87、恒值控制。</p><p>　　4-1-2 隨動(dòng)控制</p><p>　　隨動(dòng)控制是輸出隨給定變化的控制。</p><p>　　4-1-3 程序控制</p><p>　　它是給定值按固定的程序設(shè)定時(shí)間而變化，通常被用在化工生產(chǎn)中溫度的過(guò)程化控制。</p><p>　　4-2 根據(jù)控制方法分類(lèi)</p>&l

88、t;p>　　自動(dòng)控制：?jiǎn)卧刂啤?比值控制、 串級(jí)控制</p><p>　　4-2-1 比值控制</p><p>　　實(shí)現(xiàn)兩個(gè)或兩個(gè)以上參數(shù)符合一定比例關(guān)系的控制系統(tǒng)，通常以保持兩種或幾種物料的流量為一定比例關(guān)系的系統(tǒng)。</p><p>　　經(jīng)過(guò)比較、測(cè)量確定兩種物料中處于主導(dǎo)地位物料便于實(shí)現(xiàn)比值控制。</p><p><b>

89、;　　6、自動(dòng)控制部分</b></p><p>　　下面將要介紹各個(gè)部分對(duì)于反饋控制是必不可少的。</p><p>　　基本檢測(cè)單元、執(zhí)行單元、 控制單元</p><p><b>　　6-1基本檢測(cè)要素</b></p><p>　　在控制設(shè)備中，這是從被控對(duì)象上提取重要的信號(hào)的部分。用壓力檢測(cè)的基本要素如下：

90、</p><p>　　6-1-1 流量檢測(cè)</p><p>　　我們通常辨別物質(zhì)為三種狀態(tài)：固體、液體、氣體。固體的形狀是固定的，幾乎不能改變。液體是容易改變形狀和體積的。在三種物態(tài)中，液體和氣體被通稱(chēng)為流體。</p><p>　　單位時(shí)間里通過(guò)一定區(qū)域的流動(dòng)流體的體積或質(zhì)量稱(chēng)為流量。測(cè)量流量有以下幾</p><p>　　種方法：（１）差壓

91、式流量計(jì)</p><p>　　將一個(gè)節(jié)流裝置即帶孔的金屬盤(pán)放在流體流過(guò)的管子中，流體在通過(guò)盤(pán)前后是產(chǎn)生不同的壓力。流體通過(guò)節(jié)流裝置時(shí)，節(jié)流裝置的上游、下游之間產(chǎn)生壓差。這個(gè)壓差與流量有關(guān)，所以我們就可以通過(guò)測(cè)量這個(gè)壓力差得到流量。</p><p><b>　　（２）轉(zhuǎn)子流量計(jì)</b></p><p>　　將浮子放入一個(gè)錐形管子中，被測(cè)流體由底部

92、向上漲，引起浮子上移。浮子上移的數(shù)量與流量有關(guān)，這個(gè)值隨流量改變。</p><p><b>　?。ǎ常╇姶帕髁坑?jì)</b></p><p>　　在磁感應(yīng)強(qiáng)度均勻的磁場(chǎng)中，垂直于磁場(chǎng)方向放置一個(gè)不導(dǎo)磁的管道，在該管道上與磁場(chǎng)垂直方向設(shè)置一對(duì)同被測(cè)介質(zhì)相接觸的電極，管道與電極之間絕緣。當(dāng)導(dǎo)電流體流過(guò)管道時(shí)，相當(dāng)于一根長(zhǎng)度為管道內(nèi)徑Ｄ的導(dǎo)線(xiàn)在切割磁力線(xiàn)，因而產(chǎn)生了感應(yīng)電勢(shì)，并

93、由兩個(gè)電極引出。感應(yīng)電勢(shì)與被測(cè)介質(zhì)的流量成線(xiàn)性關(guān)系。</p><p><b>　?。ǎ矗┏暡髁坑?jì)</b></p><p>　　超聲波在流體中的傳播速度與流體的平均流量有關(guān)?？梢酝ㄟ^(guò)測(cè)量傳播速度、管長(zhǎng)、流體流動(dòng)的速度來(lái)確定流量。 （５）動(dòng)態(tài)壓力流量計(jì)</p><p>　　裝在管子中心的元件獲得的功率與流量的２倍成正例。因此當(dāng)功率傳送到

94、上面的傳感器時(shí)，就可以知道流量的大小。</p><p>　?。ǎ叮E圓齒輪流量計(jì)</p><p>　　當(dāng)流體有下向上流過(guò)，由于壓力損失，使出口和入口產(chǎn)生壓差，橢圓齒輪在此壓差作用下產(chǎn)生力矩而轉(zhuǎn)動(dòng)。當(dāng)橢圓齒輪與殼間的半月牙容積Ｖ一定時(shí)，只要測(cè)出橢圓齒輪的轉(zhuǎn)速Ｎ，便可知被測(cè)流體的體積流量Ｑ，即</p><p><b>　?。眩剑矗危?lt;/b><

95、/p><p><b>　?。?）水壩式流量計(jì)</b></p><p>　　在水流的方向上建以個(gè)水壩，讓水流流過(guò)壩，使水流增大，水位升高。這就固定了流量與壩形狀的關(guān)系?？梢酝ㄟ^(guò)壩的表面和高度知道流量。</p><p>　　直角三角壩： Q=Kh5/2(m/h)</p><p>　　方型壩：

96、Q=Kbh3/2(m/h)</p><p>　　一般壩： Q=Kbh3/2(m/h)</p><p>　　6-1-2電磁流量計(jì)的使用原理</p><p>　　電磁流量計(jì)用于流量控制實(shí)驗(yàn)設(shè)備（SPC-315）中測(cè)量流量。</p><p>　　電磁流量計(jì)的原理是根據(jù)法拉弟定律當(dāng)流體在磁場(chǎng)中流動(dòng)時(shí)產(chǎn)生的感應(yīng)電動(dòng)勢(shì)與流速成正比。

97、產(chǎn)生的感應(yīng)電勢(shì)是垂直于電磁場(chǎng)方向和液體流動(dòng)方向，可通過(guò)右手定則判斷。電磁流量計(jì)將產(chǎn)生的感應(yīng)電動(dòng)勢(shì)轉(zhuǎn)換成4-20mA的統(tǒng)一標(biāo)準(zhǔn)直流電信號(hào)。</p><p>　　感應(yīng)電動(dòng)勢(shì)E的大小用下式表示：</p><p>　　E=D·V·B (1)</p><p><b>　　E：表示感應(yīng)電

98、勢(shì)</b></p><p><b>　　B：磁感應(yīng)強(qiáng)度</b></p><p><b>　　D：管道內(nèi)徑</b></p><p><b>　　V：流體的平均流速</b></p><p>　　流量表示為Q[M/S]</p><p>　　Q=

99、 （2）</p><p>　　所以感應(yīng)電勢(shì)E被表示為 E= （3）</p><p>　　從式（3）中可知，感應(yīng)電勢(shì)E是和流量Q成正比的。</p><p>　　電磁流量計(jì)的正確使用條件：</p><p>　　1. 被測(cè)介質(zhì)具有導(dǎo)電性；&l

100、t;/p><p>　　2. 測(cè)量管道內(nèi)充滿(mǎn)液體；</p><p>　　3. 液體是單一物質(zhì)；</p><p>　　4. 流體是無(wú)磁性的。</p><p>　　6-2 執(zhí)行單元（控制閥）</p><p>　　控制閥是過(guò)程控制系統(tǒng)的一個(gè)重要組成部分，其接受過(guò)程反饋數(shù)據(jù)的調(diào)節(jié)并將其轉(zhuǎn)換后對(duì)過(guò)程進(jìn)行控制。因此，閥的特性對(duì)控制質(zhì)量

101、至管重要。</p><p>　　6-2-1控制閥特性</p><p><b>　　理想的流量特性</b></p><p>　　控制閥的流量特性是指閥的操作信號(hào)與流量之間的關(guān)系。可分為直線(xiàn)特性，等百分比特性和開(kāi)關(guān)特性。</p><p>　　直線(xiàn)特性、百分比特性、開(kāi)關(guān)特性</p><p><b&

102、gt;　?、僦本€(xiàn)特性</b></p><p>　　閥的開(kāi)度與流量成比例關(guān)系。即閥的開(kāi)度改變10%，其流量也改變10%。</p><p><b>　?、诘劝俜直忍匦?lt;/b></p><p>　　閥桿的單位相對(duì)位移（開(kāi)度）變化所引起的相對(duì)流量變化與該點(diǎn)的相對(duì)流量成正比。例如，</p><p>　　量增加率為10%

103、，閥的開(kāi)度將變化n%。</p><p>　　當(dāng)開(kāi)度為10%，其流量變化為 10×0.1=1L/min</p><p>　　當(dāng)開(kāi)度為 50%，其流量變化為 50 ×0.1=5L/min</p><p>　　當(dāng)開(kāi)度為90%，其流量變化為 90 ×0.1=9L/min</p><p>　　即使同樣是n%

104、的開(kāi)度，流量的變化也很小。所以利用等百分比流量特性是有利的，控制閥在小開(kāi)度時(shí)，控制作用緩和平穩(wěn)，控制閥在大開(kāi)度是，控制及時(shí)有效。</p><p><b>　?、劭扉_(kāi)特性</b></p><p>　　當(dāng)閥開(kāi)始移動(dòng)時(shí)，流量很快到達(dá)最大值。它通常用在二位控制系統(tǒng)中。它被稱(chēng)</p><p>　　為開(kāi)關(guān)特性又叫快開(kāi)特性。</p><p

105、>　　1、研究PID的值與系統(tǒng)抗擾能力及系統(tǒng)對(duì)突加給定的響應(yīng)的關(guān)系。</p><p>　　通過(guò)實(shí)驗(yàn)的數(shù)據(jù)找出PID參數(shù)與擾動(dòng)響應(yīng)的關(guān)系。</p><p><b>　　比例環(huán)節(jié)的作用</b></p><p><b>　　·增大比例系數(shù)</b></p><p>　　·發(fā)生波動(dòng)，

106、搜索狀況</p><p><b>　　·減少調(diào)節(jié)時(shí)間</b></p><p><b>　　微分環(huán)節(jié)作用</b></p><p>　　通過(guò)實(shí)驗(yàn)只改變微分時(shí)間TD，使TD變大，可以得到以下結(jié)論</p><p>　　·系統(tǒng)有靜差（在無(wú)積分作用時(shí)）</p><p>

107、;　　·第一個(gè)峰值變小超調(diào)量減小</p><p>　　·波動(dòng)穩(wěn)定，振幅斜率變小，但如微分時(shí)間太長(zhǎng)，波形將再次振蕩</p><p><b>　　·調(diào)節(jié)時(shí)間變小</b></p><p><b>　　積分環(huán)節(jié)作用</b></p><p>　　通過(guò)實(shí)驗(yàn)只改變積分時(shí)間TI，使TI

108、變大，可以得到以下結(jié)論。</p><p><b>　　·系統(tǒng)無(wú)靜差</b></p><p>　　·第一個(gè)峰值的高度變?。ǔ{(diào)量變小）</p><p>　　·產(chǎn)生波動(dòng)，而振幅傾斜變大直至發(fā)散</p><p>　　·系統(tǒng)回復(fù)到設(shè)定值的時(shí)間變短</p><p>&

109、lt;b>　　2、PID調(diào)節(jié)過(guò)程</b></p><p>　　通過(guò)進(jìn)行實(shí)驗(yàn)理解PID的作用和特性，然而很難找到最佳調(diào)節(jié)作用的值。</p><p>　　以下過(guò)程中找到最佳的PID 值的方法：</p><p>　?。?）P-I-D在順序逐個(gè)改變參數(shù)，使響應(yīng)接近理想的值，確定并記錄結(jié)果。</p><p>　　（2）從大到小改變比例

110、放大系數(shù)，當(dāng)測(cè)量值產(chǎn)生搜索時(shí)，停止改變。</p><p>　　（3）從大到小改變積分時(shí)間，當(dāng)測(cè)量值產(chǎn)生搜索時(shí)，將積分時(shí)間變大一點(diǎn)。 </p><p>　?。?）從小到大改變微分時(shí)間，當(dāng)測(cè)量值產(chǎn)生搜索時(shí)，停止改變微分時(shí)間，并將微分時(shí)間再調(diào)小一點(diǎn)。</p><p>　?。?）當(dāng)希望減小調(diào)節(jié)時(shí)間時(shí)，把比例系數(shù)調(diào)小一點(diǎn)，再檢查測(cè)量值的變化。</p><p

111、><b>　　最優(yōu)控制</b></p><p>　　根據(jù)前面的實(shí)驗(yàn)，安排設(shè)置控制目標(biāo)。</p><p>　　希望在改變?cè)O(shè)定值時(shí)，使測(cè)量值盡可能快的與設(shè)定值相同（同步跟隨測(cè)</p><p><b>　　量值的變化）。</b></p><p>　　假如由于周?chē)h(huán)境的臨時(shí)改變而導(dǎo)致測(cè)量值偏離給定，則

112、希望盡可能地</p><p>　　使測(cè)試值返回到給定值。（擾動(dòng)響應(yīng)）</p><p>　　對(duì)于第一種情況，調(diào)節(jié)時(shí)間是關(guān)鍵問(wèn)題。在給定值發(fā)生變化時(shí)，測(cè)量值在PID調(diào)節(jié)作用下改變，一般變化過(guò)程如圖（9-1），在此圖中測(cè)量值暫時(shí)超過(guò)了給定值，這被稱(chēng)為超調(diào)量。減少超調(diào)量和縮短調(diào)節(jié)時(shí)間通常不能同時(shí)滿(mǎn)足。簡(jiǎn)而言之就是調(diào)節(jié)沒(méi)有超調(diào)就會(huì)使調(diào)節(jié)時(shí)間變長(zhǎng)。同理，在過(guò)程控制中也會(huì)遇到同樣的問(wèn)題。如果減少時(shí)間，超