单片机 外文翻译 外文文献 英文文献 基于单片机的超声波测距系统的研究与设计.docx

单片机 外文翻译 外文文献 英文文献 基于单片机的超声波测距系统的研究与设计.docx

《单片机 外文翻译 外文文献 英文文献 基于单片机的超声波测距系统的研究与设计.docx》由会员分享，可在线阅读，更多相关《单片机 外文翻译 外文文献 英文文献 基于单片机的超声波测距系统的研究与设计.docx（30页珍藏版）》请在冰点文库上搜索。

单片机外文翻译外文文献英文文献基于单片机的超声波测距系统的研究与设计

单片机外文翻译外文文献英文文献基于单片机的超声波测距系统的研究与设计

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附录A

外文翻译

theequivalentdcvalue.Intheanalysisofelectroniccircuitstobeconsideredinalatercourse,bothdcandacsourcesofvoltagewillbeappliedtothesamenetwork.Itwillthenbenecessarytoknowordeterminethedc（oraveragevalue）andaccomponentsofthevoltageorcurrentinvariouspartsofthesystem.

EXAMPLE13.13DeterminetheaveragevalueofthewaveformsofFig.13.37.

FIG.13.37

Example13.13.

Solutions:

a.Byinspection,theareaabovetheaxisequalstheareabelowoveronecycle,resultinginanaveragevalueofzerovolts.

b.UsingEq.（13.26）:

asshowninFig.13.38.

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Inreality,thewaveformofFig.13.37（b）issimplythesquarewaveofFig.13.37（a）withadcshiftof4V;thatisv2=v1+4V

EXAMPLE13.14Findtheaveragevaluesofthefollowingwaveformsoveronefullcycle:

a.Fig.13.39.

b.Fig.13.40.

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Solutions:

Wefoundtheareasunderthecurvesintheprecedingexamplebyusingasimplegeometricformula.Ifweshouldencounterasinewaveoranyotherunusualshape,however,wemustfindtheareabysomeothermeans.Wecanobtainagoodapproximationoftheareabyattemptingtoreproducetheoriginalwaveshapeusinganumberofsmallrectanglesorotherfamiliarshapes,theareaofwhichwealreadyknowthroughsimplegeometricformulas.Forexample,

theareaofthepositive（ornegative）pulseofasinewaveis2Am.Approximatingthiswaveformbytwotriangles（Fig.13.43）,weobtain（usingarea

1/2baseheightfortheareaofatriangle）aroughideaoftheactualarea:

Acloserapproximationmightbearectanglewithtwosimilartriangles（Fig.13.44）:

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whichiscertainlyclosetotheactualarea.Ifaninfinitenumberofformswereused,anexactanswerof2Amcouldbeobtained.Forirregularwaveforms,thismethodcanbeespeciallyusefulifdatasuchastheaveragevaluearedesired.Theprocedureofcalculusthatgivestheexactsolution2Amisknownasintegration.Integrationis

presentedhereonlytomakethemethodrecognizabletothereader;itisnotnecessarytobeproficientinitsusetocontinuewiththistext.Itisausefulmathematicaltool,however,andshouldbelearned.Findingtheareaunderthepositivepulseofasinewaveusingintegration,wehave

where?

isthesignofintegration,0andparethelimitsofintegration,Amsinaisthe

functiontobeintegrated,anddaindicatesthatweareintegratingwithrespecttoa.

Integrating,weobtain

Sinceweknowtheareaunderthepositive（ornegative）pulse,wecaneasilydeterminetheaveragevalueofthepositive（ornegative）regionofasinewavepulsebyapplyingEq.（13.26）:

ForthewaveformofFig.13.45,

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EXAMPLE13.15DeterminetheaveragevalueofthesinusoidalwaveformofFig.13.46.

Solution:

Byinspectionitisfairlyobviousthat

theaveragevalueofapuresinusoidalwaveformoveronefullcycleiszero.

EXAMPLE13.16DeterminetheaveragevalueofthewaveformofFig.13.47.

Solution:

Thepeak-to-peakvalueofthesinusoidalfunctionis16mV+2mV=18mV.Thepeakamplitudeofthesinusoidalwaveformis,therefore,18mV/2=9mV.Countingdown9mVfrom2mV（or9mVupfrom-16mV）resultsinanaverageordclevelof-7mV,asnotedbythedashedlineofFig.13.47.

EXAMPLE13.17DeterminetheaveragevalueofthewaveformofFig.13.48.

Solution:

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EXAMPLE13.18ForthewaveformofFig.13.49,determinewhethertheaverage

valueispositiveornegative,anddetermineitsapproximatevalue.

Solution:

Fromtheappearanceofthewaveform,theaveragevalueispositiveandinthevicinityof2mV.Occasionally,judgmentsofthistypewillhavetobemade.Instrumentation

Thedcleveloraveragevalueofanywaveformcanbefoundusingadigitalmultimeter（DMM）oranoscilloscope.Forpurelydccircuits,simplysettheDMMondc,andread

thevoltageorcurrentlevels.Oscilloscopesarelimitedtovoltagelevelsusingthesequenceofstepslistedbelow:

1.FirstchooseGNDfromtheDC-GND-ACoptionlistassociatedwitheachverticalchannel.TheGNDoptionblocksanysignaltowhichtheoscilloscopeprobemaybeconnectedfromenteringtheoscilloscopeandrespondswithjustahorizontalline.Settheresultinglineinthemiddleoftheverticalaxisonthehorizontalaxis,asshowninFig.13.50（a）.

2.Applytheoscilloscopeprobetothevoltagetobemeasured（ifnotalreadyconnected）,andswitchtotheDCoption.Ifadcvoltageispresent,thehorizontallinewillshiftupordown,asdemonstratedinFig.13.50（b）.Multiplyingtheshiftbytheverticalsensitivitywillresultinthedcvoltage.Anupwardshiftisapositivevoltage（higher

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potentialattheredorpositiveleadoftheoscilloscope）,whileadownwardshiftisanegativevoltage（lowerpotentialattheredorpositiveleadoftheoscilloscope）.Ingeneral,

1.UsingtheGNDoption,resetthehorizontallinetothemiddleofthescreen.2.SwitchtoAC（alldccomponentsofthesignaltowhichtheprobeisconnectedwillbeblockedfromenteringtheoscilloscope—onlythealternating,orchanging,

componentswillbedisplayed）.

Notethelocationofsomedefinitivepointonthewaveform,suchasthebottomofthehalf-waverectifiedwaveformofFig.13.51（a）;thatis,noteitspositionontheverticalscale.Forthefuture,wheneveryouusetheACoption,keepinmindthatthecomputerwilldistributethewaveformaboveandbelowthehorizontalaxissuchthattheaveragevalueiszero;thatis,theareaabovetheaxiswillequaltheareabelow.3.ThenswitchtoDC（topermitboththedcandtheaccomponentsofthewaveformtoentertheoscilloscope）,andnotetheshiftinthechosenlevelofpart2,asshowninFig.13.51（b）.Equation

（13.29）canthenbeusedtodeterminethedcoraveragevalueofthewaveform.ForthewaveformofFig.13.51（b）,theaveragevalueisabout

TheprocedureoutlinedabovecanbeappliedtoanyalternatingwaveformsuchastheoneinFig.13.49.InsomecasestheaveragevaluemayrequiremovingthestartingpositionofthewaveformundertheACoptiontoadifferentregionofthescreenorchoosingahighervoltagescale.DMMscanreadtheaverageordclevelofanywaveformbysimplychoosingtheappropriatescale.

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13.7EFFECTIVE（rms）VALUES

Thissectionwillbegintorelatedcandacquantitieswithrespecttothepowerdeliveredtoaload.Itwillhelpusdeterminetheamplitudeofasinusoidalaccurrentrequiredtodeliverthesamepowerasaparticulardccurrent.Thequestionfrequentlyarises,Howisitpossibleforasinusoidalacquantitytodeliveranetpowerif,overafullcycle,thenetcurrentinanyonedirectioniszero（averagevalue0）?

Itwouldalmostappearthatthepowerdeliveredduringthepositiveportionofthesinusoidalwaveformiswithdrawnduringthenegativeportion,andsincethetwoareequalinmagnitude,thenetpowerdeliverediszero.However,understandthatirrespectiveofdirection,current

ofanymagnitudethrougharesistorwilldeliverpowertothatresistor.Inotherwords,

duringthepositiveornegativeportionsofasinusoidalaccurrent,powerisbeingdeliveredateach

instantoftimetotheresistor.Thepowerdeliveredateachinstantwill,ofcourse,varywiththemagnitudeofthesinusoidalaccurrent,buttherewillbeanetflowduringeitherthepositiveorthenegativepulseswithanetflowoverthefullcycle.Thenetpowerflowwillequaltwicethatdeliveredbyeitherthepositiveorthenegativeregionsofsinusoidalquantity.AfixedrelationshipbetweenacanddcvoltagesandcurrentscanbederivedfromtheexperimentalsetupshowninFig.13.52.Aresistorinawaterbathisconnectedbyswitchestoadcandanacsupply.Ifswitch1isclosed,adccurrentI,

determinedbytheresistanceRandbatteryvoltageE,willbeestablishedthroughthe

resistorR.Thetemperaturereachedbythewaterisdeterminedbythedcpowerdissipatedintheformofheatbytheresistor.

Ifswitch2isclosedandswitch1leftopen,theaccurrentthroughtheresistorwillhaveapeakvalueofIm.Thetemperaturereachedbythewaterisnowdeterminedbytheacpowerdissipatedintheformofheatbytheresistor.Theacinputisvarieduntilthetemperatureisthesameasthatreachedwiththedcinput.Whenthisisaccomplished,theaverageelectricalpowerdeliveredtotheresistorRbytheacsourceisthesameas

thatdeliveredbythedcsource.Thepowerdeliveredbytheacsupplyatanyinstantoftimeis

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Theaveragepowerdeliveredbytheacsourceisjustthefirstterm,sincetheaveragevalueofacosinewaveiszeroeventhoughthewavemayhavetwicethefrequencyoftheoriginalinputcurrentwaveform.Equatingtheaveragepowerdeliveredbytheacgeneratortothatdeliveredbythedcsource,

which,inwords,statesthat

theequivalentdcvalueofasinusoidalcurrentorvoltageis1/2or0.707ofits

maximumvalue.

Theequivalentdcvalueiscalledtheeffectivevalueofthesinusoidalquantity.

Insummary,

Asasimplenumericalexample,itwouldrequireanaccurrentwithapeakvalueof2（10）14.14AtodeliverthesamepowertotheresistorinFig.13.52asadccurrentof10A.Theeffectivevalueofanyquantityplottedasafunctionoftimecanbefoundbyusingthefollowingequationderivedfromtheexperimentjustdescribed:

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which,inwords,statesthattofindtheeffectivevalue,thefunctioni（t）mustfirstbe

squared.Afteri（t）issquared,theareaunderthecurveisfoundbyintegration.ItisthendividedbyT,thelengthofthecycleortheperiodofthewaveform,toobtaintheaverageor