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1、一种新的基于C/V的微电容的检测方法本文研究工作得到国家高技术研究发展计划（863计划）第四批课题，（2008AA11A134）基金的部分资助。 许立志 王明灼 曾黄麟 (四川理工学院，自贡，643000)摘要:论文分析了传统及现有小电容检测方法存在的问题，基于C/V电容检测的基本原理，提出了一种新的基于C/V的微电容的检测方法，设计了一个简易的微电容运算放大器检测电路.根据电路模型分析和仿真测试结果表明，该电路具有抗杂散电容干扰强、灵敏度高、容易实现无损在线检测、成本低等优点.关键词: 微电容, 线性, 检测电路, 杂散电容中图分类号:TM53 文献标识码: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，国内外对储气井套管检测技术进行了广泛的研究，特别是对测量金属腐蚀度的无损检测方法研究十分重视，主要采用了声学检测法、射线检测法、电学检测法、磁学检测法、光学检测法等。在测量金属腐蚀度的无损检测方法，电容层析成像技术（ECT）是多相流参数检测中的一种新技术, 可提供封闭管道及容
5、器中内部的可视化信息, 具有结构简单, 采用非侵入式, 响应速度快等特点。其中电容的测量是该技术的关键部分，ECT 中的电容测量由于电容的变化量较小，一般在几个到几十皮法的范围，因此测量较困难，且要求分辨率高、数据采集速率快, 这使得许多常用的电容测量方法不能适用。如何解决抗杂散电容干扰，提高测量灵敏度，实现无损在线检测等成为研究的主要任务。本文分析了传统及现有小电容检测方法存在的问题，提出一种新的基于C/V的微电容的检测方法。2电容层析成像技术的电容测量方法在测量金属腐蚀度的无损检测中，微电容检测方法主要有谐振法1，调频法2，交流电桥法3，差动脉宽调制法，V/T法等。谐振法是在被测电容(常常
6、伴随有一漏电阻) 两端并联一个固定电感,然后加一可变频率的电源.调整信号源频率,使电路发生谐振.谐振时,被测电容 呈现的容抗和电感呈现的感抗相等,从而可求得被测电容。该方法的优点是:频率范围宽,可从几百千赫到几百兆赫,适合实验室测量,适于小电容测量.存在的问题是:工作点不好选取，变化范围较窄，导致量程不大；传感器与谐振回路要靠近，否则电缆的杂散电容对电路影响较大；为了提高测量精度，振荡器的频率稳定度要优于10的数量级，这对于信号源来说要长时间保持这种稳定度，比较困难.调频法是调频测量电路把电容式传感器作为振荡器谐振回路的一部分，称之为谐振电容，当被测输入量导致电容发生变化时，振荡器的振荡频率就
7、发生变化，将频率的变化在鉴频器中解调出与被测信号成比例的低频电压信号，再经过放大后才能输入计算机.这种调频电路特性稳定，灵敏度高，存在的问题是:响应速度慢，难以实现无损在线检测实时信号处理，因为电路中的信号频率f有变化，需要高精度电路配合，特别是要求有恒幅的幅频特性，不适合高精度电容检测的设计。交流电桥法的原理是把被测电容(可有漏导)放在一个桥臂,可调的参考阻抗放在相邻的另一个桥臂,二桥臂分别接到频率相同、电压相同的两个信号源上. 调节参考阻抗使桥路平衡,则被测桥臂中的阻抗与参考阻抗共轭相等. 此法的优点是:精度高,适合做精密电容测量,可以做到高SNR。存在的问题是: 由于此电路只针对差动电容
8、的测量，而不能测量出单电容的绝对值，且不具备自动平衡措施,构成电路复杂,且激励频率通常低于100 kHz。差动脉宽调制法的工作原理是:作为传感器的电容器充放电时，电容量的变化使电路输出的脉冲宽度随之变化，经低通滤波器得到与被测量相对应的直流信号。该电路输出电压与各电容传感器的变化量的代数和成正比。存在的问题是:此电路要求直流电源电压稳定性要高，输出电压信号一般为矩形波，需要再配一低通滤波器才能得到直流信号。V/T法测量，根据充放电原理，采用间歇式CN转换电路，通过控制间歇式转换电路中模拟开关的开关时序以完成对被测电容的充放电;实现被测电容值转换成可供模拟转换的电压值。存在的问题是:对被测电容值
9、小、电容变化甚微、易受外部环境干扰，测量精度不高，对恒流源要求较高，温度漂移对测量精度影响较大，存在过零器的重复性误差，测量速度慢，受单片机等控制起的晶振频率的限制等。3 一种新的基于基于电容电压的微电容的检测方法在电容层析成像技术 电容测量中，电容传感器内充以两相介质时，两电极间互电容的变化量是流体相含率及其空间分布的函数 ,而相含率变化所引起的互电容变化量一般为0.11.0pf左右，且不同的电极对之间的电容量相差很大，相邻电极对间的电容比相对电极对间的电容要大数百倍，同时杂散电容远远大于待测电容，因此应用于电容层析成像技术的电容检测应当具有以下特点：（1）检测系统结构简单, 响应速度快等特
10、点。（2）)测量范围足够宽，分辨率高、数据采集速率快 (3)低漂移、能抑制杂散电容、消除损耗电导的影响。 (4) 线性度好，非线性误差小，高信噪比。因此我们提出一种新的基于基于电容电压的微电容的检测电路，应当具有以下特点：(1) 检测电路结构简单, 响应速度快；（2）低漂移、能抑制杂散电容、消除损耗电导的影响，高信噪比；(3)高分辨率，测量范围宽，线性度好，非线性误差小。基于电容电压的微电容的运算放大检测电路如图1所示。图1 基于基于电容电压的微电容的运算放大检测电路被测量微电容，为参考电容, 和为固定衰减电阻, 为反馈电阻。被测微电容为可调电容,通过调节其的大小,以观察电容变化对输出的影响,
11、得出该电路的测量精度。运算放大器A1的输入阻抗很高，增益很大，A2为射极跟随器，若无双运放，这级可以省略，主要起隔离作用。由于运算放大器A1的反向输入端虚地，电路的杂散电容C两端相当于接地，对电路影响很小,因此可以省略. 为激励源电压，为输出电压。从理论上，可以不加反馈电阻，但在实际仿真的过程发现反馈电阻非常重要，在本论文的仿真试验中，反馈电阻的有无直接影响电路能否正常工作。由电路原理，有： （1）若，则根据（1）式，有： （2）由于为的参考电容，其比值相对较小，所以从（2）式可得：与的相位差为： （3） （4）因此，该电路能够从测量的输出的电压通过计算处理。得出被测电容的值，实现对微电容的测
12、量。仿真试验测试结果，本设计仿真在Multisim7.0环境下进行。试验采用输入信号采用2.5MHz，幅度为12V的正弦信号，经过和的作用，变为稳定的频率为2.5MHz，幅度为10mV的正弦信号源输入放大电路，经过大增益运算放大器A1，进行线性放大，选用的运放为:高输入阻抗;低输出阻抗;低失调电压, 低失调电流; 宽带运放。仿真结果如图24所示：图2运放输出信号的图形 图3被测电容输出图形 图4 被测电容输出图形如果输入信号和参考电容中有一个参数发生波动,即使被测电容不变,输出也随之发生了变化,从而产生了漂移. 如果电路灵敏度很高,这种漂移会给测量结果带来误差. 为了保证输出值的稳定, 输入信
13、号和参考电容应尽可能稳定,反馈电阻 的温度系数应尽可能小. 由 (4) 式 可以看出,为了提高传感器的检测灵敏度,可以通过提高时参考电容的容量、适当提供反馈电阻 达到. 但这样做的结果是使测量电路对外界干扰也变得敏感. 因此,各参数选择必须综合考虑这两方面的要求.4 结论电容成像系统的测量电路包含数字器件和模拟器件的微弱电容信号测量电路，在实际电路设计中不仅需要考虑克服分布电容的影响，还要尽量减少数字电路对模拟电路的高频干扰。因此在设计中要把每个测量电路模块独立开，模块之间用数字总线连接。并由计算机对测量过程进行控制和数据采集。实际上，最终输出值包括传感器的本体电容和被测电容。为了使转换电路的
14、最后输出量直接反映实际的被测电容的变化量，平衡掉本体电容，可以在计算机控制差分放大采用直流补偿 DAC 的方法。本文提出的基于电容电压的微电容的运算放大检测电路，该电路较好的实现了将被测微电容转换为电压，具有良好的抗杂散电容能力和抗干扰能力,线性度好,结构简单,容易实现,灵敏度高,成本低廉.且电路的工作频率较高，能够很好的防止其他电路的低频干扰。参考文献1C.Kolle.Low-cost,high-precision measurement system for capacitive sensors. Meas.Sci.Technol.No.92W.C.Heerens.Application
15、of capacitance techniques in sensors. Phys.Sci.instrum. No.193 马式勇. 射频电容式传感器的研究与应用J . 传感器技术,2001 (2) :43 - 45.4赵雪英，郭雨梅.一种小电容检测方法一充放电法J.沈阳工业大学学报，2003(1): 55-575佘生能，孙士平.电容传感器新型电容测量电路设计J.中国测试技术，2005(9):42-436马成，基于DSP的为电容快速检测系统研究.D 西南大学硕士学位论文.20087刘文宇 陈德运，电容层析成像中微小电容检测的研究，科技资讯 , 2006,(27) :42-438傅文利， 改善
16、电容层析成像的重建图像质量的方法J. 广西物理 , 2006,(03) :12-139刘武, 黄晓刚, 磁悬浮转子微陀螺的电容检测系统分析和实现J. 测控技术 , 2006,(01)：1-4 10周晓奇, 郑阳明, 基于FPGA的数字式电容检测系统J. 传感技术学报 , 2008,(04)：698-671Employment tribunals sort out disagreements between employers and employees.You may need to make a claim to an employment tribunal if: you dont agr
17、ee with the disciplinary action your employer has taken against you your employer dismisses 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 haventappealedagains
18、t the disciplinary action your employer has taken against you. However, if you win your case, 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 da
19、te when the event you are complaining about happened. If your application is received after 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 l
20、ess formal than some other courts, but it is still a legal process and you will need to give 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 a
21、way from one of the organisations listed underFurther help.If you are being represented by 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 so
22、licitor cant charge you more than 35% of your compensation if you win the case.If you are 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
23、 Advice Bureau. To find your nearest CAB, including those that give advice by e-mail, click 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,
24、 is in London for the Football Associations 150th anniversary celebrations and will attend 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
25、 to find out what his experience was.Uefa hasopened disciplinary proceedings against CSKAfor 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 wer
26、e surprised and disappointed by Toures complaint. In a statement the Russian side added: We found no racist insults from fans of CSKA.待添加的隐藏文字内容3Age 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; Ma
27、y be back in the past, to oneself the paranoid weird belief disillusionment, these days, my mind has 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.一字开头的年龄已经到了尾声
28、。或许是愧疚于自己似乎把转瞬即逝的很多个不同的日子过成了同一天的样子；或许是追溯过去，对自己那些近乎偏执的怪异信念的醒悟，这些天以来，思绪一直很凌乱，在脑海中不断纠缠。总觉得自己自己似乎应该去做点什么，或者写点什么。二十年的人生轨迹深深浅浅，突然就感觉到有些事情，非做不可了。The end of our life, and can meet many things really do?而穷尽我们的一生，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 Yea
29、r, but as the advance of the age, will be more and more found that those things are optional; Junior 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
30、so important; Then in high school, think dont want to give vent to out your inner voice can be in the 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 bas
31、ketball hoops, suddenly found himself has already cant remember his appearance.童年时，觉得压岁钱和新衣服是过年必备，但是随着年龄的推进，会越来越发现，那些东西根本就可有可无；初中时，以为要有一场暗恋才意味着真正的成长，但三年过去后，自己心平气和的写同学录的时候，突然就发现是不是真正的成长了，好像并没有那么重要了；然后到了高中，觉得非要吐露出自己的心声才能为高中生涯里的懵懂情愫划上一个句点，但毕业晚会的时候最终还是被梗塞在了咽喉，后来再次站在他曾经挥汗如雨的球场，看着他投过篮球的球框时，突然间发现自己已经想不起他的容
32、颜。Originally, this world, can produce a chemical reaction to an event, in addition to resolutely, have to do, and time.原来，这个世界上，对某个事件能产生化学反应的，除了非做不可的坚决，还有，时间。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 deter
33、mined to do something, but more often is he backed out at last. Dislike his cowardice, finally found 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.一个人的
34、时候，自己的想法总是特别地清晰。想要的，不想要的，界限明确，好像没有什么可以撼动自己。也曾经好像已经下定了决心去做某件事，但更多的时候是最后又打起了退堂鼓。嫌恶过自己的怯懦，最终却发现有很多缘分，有很多错过，好像冥冥之中真的已经注定。那些曾经所谓的非做不可，只是青葱年华里自己给自己注射的一支强心剂，或者说，是自以为是的精神寄托罢了。At the moment, the sky is dark, the air is fresh factor after just rained. Suddenly thought of blue plaid shirt; Those were broken in
35、to various shapes of stationery; From the corner at the beginning of deep friendship; Have declared the end of the encounter that havent start planning. Those years, those days of do, finally, like youth, will end in our life.此刻，天空是阴暗的，空气里有着刚下过雨之后的清新因子。突然想到那件蓝格子衬衫；那些被折成各种各样形状的信纸；那段从街角深巷伊始的友谊；还有那场还没有
36、开始就宣告了终结的邂逅计划那些年那些天的非做不可，终于和青春一样，都将在我们的人生中谢幕。Baumgartner the disappointing news: Mission aborted. r plays 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 c
37、apsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-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 kilometer
38、s) 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 o
39、nto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving
40、 into the shallow end. Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough t
41、o stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In
42、 order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).cause there
