資源描述：
《data acquisition via labview》由會(huì)員上傳分享，免費(fèi)在線閱讀，更多相關(guān)內(nèi)容在行業(yè)資料-天天文庫。
1、7LABORATORYAUTOMATION:DECAYOFACAPACITORPurpose:Asanintroductiontolaboratoryautomation,thedecayconstantofanRCcircuitismeasuredusinganIBM-PCcomputer.ThecomputerisprogrammedusingthegraphicallanguageLabVIEWtocontroltheexperiment,gatherthedata,andanalyzethedata.References:Usin
2、gLabVIEWvideotape,NationalInstruments,Austin,TX,1996.LabVIEWTutorialManual,NationalInstruments,Austin,TX,1996.(RefertotheotherLabVIEWmanualsasneeded.)Introduction:Figure1illustratesthegeneralideaoftheexperiment.Whentheswitchisinposition1,apowersupplywithinternalresistance
3、RiandemfEchargesacapacitorCinserieswitharesistanceR.Whentheswitchissettoposition2,thecapacitorisdischargedthroughtheresistorR.Ratherthanswitchingmanuallyorswitchingviaarelay(arelativelyslowdevice),atransistorswitchisemployed.Thetransistorcircuit(alreadyconstructedforyou)i
4、sillustratedinFigure2.Thetransistorswitchpositioncanbecontrolledbythecomputer’slogic.Whena7Apotentialdifferenceof0volts(logicalFalse)isappliedviathedigitaloutputofthecomputertothecircuit,transistorAisturnedoffandBisturnedon.LogicalFalsemeansthattheintegernumberzeroisloade
5、dintotheregisterthatcontrolsthetransistorswitch.CurrentthenflowsthroughtheRCnetwork,chargingthecapacitor.When+3.5volts(logicalTrue)isappliedtothetransistorcircuit,theswitchingreversescausingcurrenttoflowthroughthesetupresistortodischargethecapacitor.Thedecayofthevoltageof
6、thiscircuitduringadischargecycleisexponential.Anequivalentcircuitforthenetworkconsistsofaresistorandacapacitorinseriesinasingleloop.ItfollowsfromKirchhoff'ssecondrulethatIR+q/C=0,whereqisthechargeonthecapacitor.Differentiatingwithrespecttotime,oneobtainsR(dI/dt)+(dq/dt)/C
7、=0.Sincedq/dt=I,thendI/dt+I/RC=0.Rearranging,dI/I=-dt/RC.IntegratingyieldsI=Ioexp(-t/RC).UsingV=IR,wehaveV=Voexp(-t/RC).RCisoftencalledthetimeconstantofthedischargecircuit.Experimental:1.ProgrammingwiththeWindows95versionofLabVIEWispresentedinthetutorialmanualandthevideot
8、ape.ViewthevideotapebeforecomingtolabwiththegoalofobtaininganoverviewofLabVIEW.Duringthefirstaft
