畢業(yè)設(shè)計一種新的基于CV的微電容的檢測方法

1、一種新的基于C/V的微電容的檢測方法本文研究工作得到國家高技術(shù)研究發(fā)展計劃（863計劃）第四批課題，（2008AA11A134）基金的部分資助。 許立志 王明灼 曾黃麟 (四川理工學(xué)院，自貢，643000)摘要:論文分析了傳統(tǒng)及現(xiàn)有小電容檢測方法存在的問題，基于C/V電容檢測的基本原理，提出了一種新的基于C/V的微電容的檢測方法，設(shè)計了一個簡易的微電容運算放大器檢測電路.根據(jù)電路模型分析和仿真測試結(jié)果表明，該電路具有抗雜散電容干擾強、靈敏度高、容易實現(xiàn)無損在線檢測、成本低等優(yōu)點.關(guān)鍵詞: 微電容, 線性, 檢測電路, 雜散電容中圖分類號:TM53 文獻(xiàn)標(biāo)識碼:AA New Approach o

2、f Micro-capacitor Measurment Based on Conversion of Capacitances and Voltages Lizhi Xu Mingzhuo Wang Huanglin Zeng( Sichuan University of Science and Engineering, 643000, P. R. China )ABSRACT: in this Paper, some of techniques for measuring of small capacitance are briefly discussed. A kind of simpl

3、e operational amplifier circuit is designed on the basic principle of Conversion of Capacitances and Voltages (C / V) to detect the micro-capacitor. Based on analysis on capacitance detection of the circuit model and simulation test results given, It is shown that a circuit of micro-capacitor measur

4、ment based on C / V is of high sensitivity and low cost and easy for realization. Key word: micro-capacitance; Linear; detecting circuit; Stray capacitance1 引言目前，國內(nèi)外對儲氣井套管檢測技術(shù)進(jìn)行了廣泛的研究，特別是對測量金屬腐蝕度的無損檢測方法研究十分重視，主要采用了聲學(xué)檢測法、射線檢測法、電學(xué)檢測法、磁學(xué)檢測法、光學(xué)檢測法等。在測量金屬腐蝕度的無損檢測方法，電容層析成像技術(shù)（ECT）是多相流參數(shù)檢測中的一種新技術(shù), 可提供封閉管道及容

5、器中內(nèi)部的可視化信息, 具有結(jié)構(gòu)簡單, 采用非侵入式, 響應(yīng)速度快等特點。其中電容的測量是該技術(shù)的關(guān)鍵部分，ECT 中的電容測量由于電容的變化量較小，一般在幾個到幾十皮法的范圍，因此測量較困難，且要求分辨率高、數(shù)據(jù)采集速率快, 這使得許多常用的電容測量方法不能適用。如何解決抗雜散電容干擾，提高測量靈敏度，實現(xiàn)無損在線檢測等成為研究的主要任務(wù)。本文分析了傳統(tǒng)及現(xiàn)有小電容檢測方法存在的問題，提出一種新的基于C/V的微電容的檢測方法。2電容層析成像技術(shù)的電容測量方法在測量金屬腐蝕度的無損檢測中，微電容檢測方法主要有諧振法1，調(diào)頻法2，交流電橋法3，差動脈寬調(diào)制法，V/T法等。諧振法是在被測電容(常常

6、伴隨有一漏電阻) 兩端并聯(lián)一個固定電感,然后加一可變頻率的電源.調(diào)整信號源頻率,使電路發(fā)生諧振.諧振時,被測電容 呈現(xiàn)的容抗和電感呈現(xiàn)的感抗相等,從而可求得被測電容。該方法的優(yōu)點是:頻率范圍寬,可從幾百千赫到幾百兆赫,適合實驗室測量,適于小電容測量.存在的問題是:工作點不好選取，變化范圍較窄，導(dǎo)致量程不大；傳感器與諧振回路要靠近，否則電纜的雜散電容對電路影響較大；為了提高測量精度，振蕩器的頻率穩(wěn)定度要優(yōu)于10的數(shù)量級，這對于信號源來說要長時間保持這種穩(wěn)定度，比較困難.調(diào)頻法是調(diào)頻測量電路把電容式傳感器作為振蕩器諧振回路的一部分，稱之為諧振電容，當(dāng)被測輸入量導(dǎo)致電容發(fā)生變化時，振蕩器的振蕩頻率就

7、發(fā)生變化，將頻率的變化在鑒頻器中解調(diào)出與被測信號成比例的低頻電壓信號，再經(jīng)過放大后才能輸入計算機.這種調(diào)頻電路特性穩(wěn)定，靈敏度高，存在的問題是:響應(yīng)速度慢，難以實現(xiàn)無損在線檢測實時信號處理，因為電路中的信號頻率f有變化，需要高精度電路配合，特別是要求有恒幅的幅頻特性，不適合高精度電容檢測的設(shè)計。交流電橋法的原理是把被測電容(可有漏導(dǎo))放在一個橋臂,可調(diào)的參考阻抗放在相鄰的另一個橋臂,二橋臂分別接到頻率相同、電壓相同的兩個信號源上. 調(diào)節(jié)參考阻抗使橋路平衡,則被測橋臂中的阻抗與參考阻抗共軛相等. 此法的優(yōu)點是:精度高,適合做精密電容測量,可以做到高SNR。存在的問題是: 由于此電路只針對差動電容

8、的測量，而不能測量出單電容的絕對值，且不具備自動平衡措施,構(gòu)成電路復(fù)雜,且激勵頻率通常低于100 kHz。差動脈寬調(diào)制法的工作原理是:作為傳感器的電容器充放電時，電容量的變化使電路輸出的脈沖寬度隨之變化，經(jīng)低通濾波器得到與被測量相對應(yīng)的直流信號。該電路輸出電壓與各電容傳感器的變化量的代數(shù)和成正比。存在的問題是:此電路要求直流電源電壓穩(wěn)定性要高，輸出電壓信號一般為矩形波，需要再配一低通濾波器才能得到直流信號。V/T法測量，根據(jù)充放電原理，采用間歇式CN轉(zhuǎn)換電路，通過控制間歇式轉(zhuǎn)換電路中模擬開關(guān)的開關(guān)時序以完成對被測電容的充放電;實現(xiàn)被測電容值轉(zhuǎn)換成可供模擬轉(zhuǎn)換的電壓值。存在的問題是:對被測電容值

9、小、電容變化甚微、易受外部環(huán)境干擾，測量精度不高，對恒流源要求較高，溫度漂移對測量精度影響較大，存在過零器的重復(fù)性誤差，測量速度慢，受單片機等控制起的晶振頻率的限制等。3 一種新的基于基于電容電壓的微電容的檢測方法在電容層析成像技術(shù) 電容測量中，電容傳感器內(nèi)充以兩相介質(zhì)時，兩電極間互電容的變化量是流體相含率及其空間分布的函數(shù) ,而相含率變化所引起的互電容變化量一般為0.11.0pf左右，且不同的電極對之間的電容量相差很大，相鄰電極對間的電容比相對電極對間的電容要大數(shù)百倍，同時雜散電容遠(yuǎn)遠(yuǎn)大于待測電容，因此應(yīng)用于電容層析成像技術(shù)的電容檢測應(yīng)當(dāng)具有以下特點：（1）檢測系統(tǒng)結(jié)構(gòu)簡單, 響應(yīng)速度快等特

10、點。（2）)測量范圍足夠?qū)?，分辨率高、?shù)據(jù)采集速率快 (3)低漂移、能抑制雜散電容、消除損耗電導(dǎo)的影響。 (4) 線性度好，非線性誤差小，高信噪比。因此我們提出一種新的基于基于電容電壓的微電容的檢測電路，應(yīng)當(dāng)具有以下特點：(1) 檢測電路結(jié)構(gòu)簡單, 響應(yīng)速度快；（2）低漂移、能抑制雜散電容、消除損耗電導(dǎo)的影響，高信噪比；(3)高分辨率，測量范圍寬，線性度好，非線性誤差小?；陔娙蓦妷旱奈㈦娙莸倪\算放大檢測電路如圖1所示。圖1 基于基于電容電壓的微電容的運算放大檢測電路被測量微電容，為參考電容, 和為固定衰減電阻, 為反饋電阻。被測微電容為可調(diào)電容,通過調(diào)節(jié)其的大小,以觀察電容變化對輸出的影響,

11、得出該電路的測量精度。運算放大器A1的輸入阻抗很高，增益很大，A2為射極跟隨器，若無雙運放，這級可以省略，主要起隔離作用。由于運算放大器A1的反向輸入端虛地，電路的雜散電容C兩端相當(dāng)于接地，對電路影響很小,因此可以省略. 為激勵源電壓，為輸出電壓。從理論上，可以不加反饋電阻，但在實際仿真的過程發(fā)現(xiàn)反饋電阻非常重要，在本論文的仿真試驗中，反饋電阻的有無直接影響電路能否正常工作。由電路原理，有： （1）若，則根據(jù)（1）式，有： （2）由于為的參考電容，其比值相對較小，所以從（2）式可得：與的相位差為： （3） （4）因此，該電路能夠從測量的輸出的電壓通過計算處理。得出被測電容的值，實現(xiàn)對微電容的測

12、量。仿真試驗測試結(jié)果，本設(shè)計仿真在Multisim7.0環(huán)境下進(jìn)行。試驗采用輸入信號采用2.5MHz，幅度為12V的正弦信號，經(jīng)過和的作用，變?yōu)榉€(wěn)定的頻率為2.5MHz，幅度為10mV的正弦信號源輸入放大電路，經(jīng)過大增益運算放大器A1，進(jìn)行線性放大，選用的運放為:高輸入阻抗;低輸出阻抗;低失調(diào)電壓, 低失調(diào)電流; 寬帶運放。仿真結(jié)果如圖24所示：圖2運放輸出信號的圖形 圖3被測電容輸出圖形 圖4 被測電容輸出圖形如果輸入信號和參考電容中有一個參數(shù)發(fā)生波動,即使被測電容不變,輸出也隨之發(fā)生了變化,從而產(chǎn)生了漂移. 如果電路靈敏度很高,這種漂移會給測量結(jié)果帶來誤差. 為了保證輸出值的穩(wěn)定, 輸入信

13、號和參考電容應(yīng)盡可能穩(wěn)定,反饋電阻 的溫度系數(shù)應(yīng)盡可能小. 由 (4) 式 可以看出,為了提高傳感器的檢測靈敏度,可以通過提高時參考電容的容量、適當(dāng)提供反饋電阻 達(dá)到. 但這樣做的結(jié)果是使測量電路對外界干擾也變得敏感. 因此,各參數(shù)選擇必須綜合考慮這兩方面的要求.4 結(jié)論電容成像系統(tǒng)的測量電路包含數(shù)字器件和模擬器件的微弱電容信號測量電路，在實際電路設(shè)計中不僅需要考慮克服分布電容的影響，還要盡量減少數(shù)字電路對模擬電路的高頻干擾。因此在設(shè)計中要把每個測量電路模塊獨立開，模塊之間用數(shù)字總線連接。并由計算機對測量過程進(jìn)行控制和數(shù)據(jù)采集。實際上，最終輸出值包括傳感器的本體電容和被測電容。為了使轉(zhuǎn)換電路的

14、最后輸出量直接反映實際的被測電容的變化量，平衡掉本體電容，可以在計算機控制差分放大采用直流補償 DAC 的方法。本文提出的基于電容電壓的微電容的運算放大檢測電路，該電路較好的實現(xiàn)了將被測微電容轉(zhuǎn)換為電壓，具有良好的抗雜散電容能力和抗干擾能力,線性度好,結(jié)構(gòu)簡單,容易實現(xiàn),靈敏度高,成本低廉.且電路的工作頻率較高，能夠很好的防止其他電路的低頻干擾。參考文獻(xiàn)12 of capacitance techniques in sensors. Phys.Sci.instrum. No.193 馬式勇. 射頻電容式傳感器的研究與應(yīng)用J . 傳感器技術(shù),2001 (2) :43 - 45.4趙雪英，郭雨梅.

15、一種小電容檢測方法一充放電法J.沈陽工業(yè)大學(xué)學(xué)報，2003(1): 55-575佘生能，孫士平.電容傳感器新型電容測量電路設(shè)計J.中國測試技術(shù)，2005(9):42-436馬成，基于DSP的為電容快速檢測系統(tǒng)研究.D 西南大學(xué)碩士學(xué)位論文.20087劉文宇 陳德運，電容層析成像中微小電容檢測的研究，科技資訊 , 2006,(27) :42-438傅文利， 改善電容層析成像的重建圖像質(zhì)量的方法J. 廣西物理 , 2006,(03) :12-139劉武, 黃曉剛, 磁懸浮轉(zhuǎn)子微陀螺的電容檢測系統(tǒng)分析和實現(xiàn)J. 測控技術(shù) , 2006,(01)：1-4 10周曉奇, 鄭陽明, 基于FPGA的數(shù)字式電

16、容檢測系統(tǒng)J. 傳感技術(shù)學(xué)報 , 2008,(04)：698-671g an employment tribunal claiEmployment tribunals sort out disagreements between employers and employees.You may need to make a claim to an employment tribunal if: you dont agree with the disciplinary action your employer has taken against you your employer dismisse

17、s you and you think that you have been dismissed unfairly.For more information about dismissal and unfair dismissal, seeDismissal.You can make a claim to an employment tribunal, even if you haventappealedagainst the disciplinary action your employer has taken against you. However, if you win your ca

18、se, the tribunal may reduce any compensation awarded to you as a result of your failure to appeal.Remember that in most cases you must make an application to an employment tribunal within three months of the date when the event you are complaining about happened. If your application is received afte

19、r this time limit, the tribunal will not usually accept i.If you are worried about how the time limits apply to you, take advice from one of the organisations listed underFurther help.Employment tribunals are less formal than some other courts, but it is still a legal process and you will need to gi

20、ve evidence under an oath or affirmation.Most people find making a claim to an employment tribunal challenging. If you are thinking about making a claim to an employment tribunal, you should get help straight away from one of the organisations listed underFurther help.If you are being represented by

21、 a solicitor at the tribunal, they may ask you to sign an agreement where you pay their fee out of your compensation if you win the case. This is known as adamages-based agreement. In England and Wales, your solicitor cant charge you more than 35% of your compensation if you win the case.If you are

22、thinking about signing up for a damages-based agreement, you should make sure youre clear about the terms of the agreement. It might be best to get advice from an experienced adviser, for example, at a Citizens Advice Bureau. To find your nearest CAB, including those that give advice by e-mail, clic

23、k onnearest CAB.For more information about making a claim to an employment tribunal, seeEmployment tribunals.The (lack of) air up there Watch mCayman Islands-based Webb, the head of Fifas anti-racism taskforce, is in London for the Football Associations 150th anniversary celebrations and will attend

24、 Citys Premier League match at Chelsea on Sunday.I am going to be at the match tomorrow and I have asked to meet Yaya Toure, he told BBC Sport.For me its about how he felt and I would like to speak to him first to find out what his experience was.Uefa hasopened disciplinary proceedings against CSKAf

25、or the racist behaviour of their fans duringCitys 2-1 win.Michel Platini, president of European footballs governing body, has also ordered an immediate investigation into the referees actions.CSKA said they were surprised and disappointed by Toures complaint. In a statement the Russian side added: W

26、e found no racist insults from fans of CSKA.Age has reached the end of the beginning of a word. May be guilty in his seems to passing a lot of different life became the appearance of the same day; May be back in the past, to oneself the paranoid weird belief disillusionment, these days, my mind has

27、been very messy, in my mind constantly. Always feel oneself should go to do something, or write something. Twenty years of life trajectory deeply shallow, suddenly feel something, do it.一字開頭的年齡已經(jīng)到了尾聲?；蛟S是愧疚于自己似乎把轉(zhuǎn)瞬即逝的很多個不同的日子過成了同一天的樣子；或許是追溯過去，對自己那些近乎偏執(zhí)的怪異信念的醒悟，這些天以來，思緒一直很凌亂，在腦海中不斷糾纏?？傆X得自己自己似乎應(yīng)該去做點什么，

28、或者寫點什么。二十年的人生軌跡深深淺淺，突然就感覺到有些事情，非做不可了。The end of our life, and can meet many things really do?而窮盡我們的一生，又能遇到多少事情是真正地非做不可？During my childhood, think lucky money and new clothes are necessary for New Year, but as the advance of the age, will be more and more found that those things are optional; Junior

29、high school, thought to have a crush on just means that the real growth, but over the past three years later, his writing of alumni in peace, suddenly found that isnt really grow up, it seems is not so important; Then in high school, think dont want to give vent to out your inner voice can be in the

30、 high school children of the feelings in a period, but was eventually infarction when graduation party in the throat, later again stood on the pitch he has sweat profusely, looked at his thrown a basketball hoops, suddenly found himself has already cant remember his appearance.童年時，覺得壓歲錢和新衣服是過年必備，但是隨

31、著年齡的推進(jìn)，會越來越發(fā)現(xiàn)，那些東西根本就可有可無；初中時，以為要有一場暗戀才意味著真正的成長，但三年過去后，自己心平氣和的寫同學(xué)錄的時候，突然就發(fā)現(xiàn)是不是真正的成長了，好像并沒有那么重要了；然后到了高中，覺得非要吐露出自己的心聲才能為高中生涯里的懵懂情愫劃上一個句點，但畢業(yè)晚會的時候最終還是被梗塞在了咽喉，后來再次站在他曾經(jīng)揮汗如雨的球場，看著他投過籃球的球框時，突然間發(fā)現(xiàn)自己已經(jīng)想不起他的容顏。Originally, this world, can produce a chemical reaction to an event, in addition to resolutely, hav

32、e to do, and time.原來，這個世界上，對某個事件能產(chǎn)生化學(xué)反應(yīng)的，除了非做不可的堅決，還有，時間。A persons time, your ideas are always special to clear. Want, want, line is clear, as if nothing could shake his. Also once seemed to be determined to do something, but more often is he backed out at last. Dislike his cowardice, finally found

33、that there are a lot of love, there are a lot of miss, like shadow really have been doomed. Those who do, just green years oneself give oneself an arm injection, or is a self-righteous spiritual.一個人的時候，自己的想法總是特別地清晰。想要的，不想要的，界限明確，好像沒有什么可以撼動自己。也曾經(jīng)好像已經(jīng)下定了決心去做某件事，但更多的時候是最后又打起了退堂鼓。嫌惡過自己的怯懦，最終卻發(fā)現(xiàn)有很多緣分，有很多

34、錯過，好像冥冥之中真的已經(jīng)注定。那些曾經(jīng)所謂的非做不可，只是青蔥年華里自己給自己注射的一支強心劑，或者說，是自以為是的精神寄托罷了。At the moment, the sky is dark, the air is fresh factor after just rained. Suddenly thought of blue plaid shirt; Those were broken into various shapes of stationery; From the corner at the beginning of deep friendship; Have declared t

35、he end of the encounter that havent start planning. Those years, those days of do, finally, like youth, will end in our life.此刻，天空是陰暗的，空氣里有著剛下過雨之后的清新因子。突然想到那件藍(lán)格子襯衫；那些被折成各種各樣形狀的信紙；那段從街角深巷伊始的友誼；還有那場還沒有開始就宣告了終結(jié)的邂逅計劃那些年那些天的非做不可，終于和青春一樣，都將在我們的人生中謝幕。Baumgartner the disappointing news: Mission aborted. r p

36、lays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-

37、to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.The supersonic descent could happen as early as Sunda.The weatheThe balloon will slowly drift to the edge of space at 120,000 feet ( Then, I would assume, he will slowly step out onto something resembling an Olympic diving plat