基于單片機(jī)的溫度控制外文文獻(xiàn)及中文翻譯文檔良心出品

TemperatureControlUsingaMicrocontroller:AnInterdisciplinaryUndergraduateEngineeringDesignProjectJamesS.McDonaldDepartmentofEngineeringScieneeTrinityUniversitySanAntonio,TX78212Abstract:Thispaperdescribesaninterdisciplinarydesignprojectwhichwasdoneundertheauthor'ssupervisionbyagroupoffourseniorstudentsintheDepartmentofEngineeringScieneeatTrinityUniversity.Theobjectiveoftheprojectwastodevelopatemperaturecontrolsystemforanair-filledchamber.Thesystemwastoallowentryofadesiredchambertemperatureinaprescribedrangeandtoexhibitovershootandsteady-statetemperatureerroroflessthan1degreeKelvinintheactualchambertemperaturestepresponse.Thedetailsofthedesigndevelopedbythisgroupofstudents,basedonaMotorolaMC68HC05familymicrocontroller,aredescribed.Thepedagogicalvalueoftheproblemisalsodiscussedthroughadescriptionofsomeofthekeystepsinthedesignprocess.Itisshownthatthesolutionrequiresbroadknowledgedrawnfromseveralengineeringdisciplinesincludingelectrical,mechanical,andcontrolsystemsengineering.IntroductionThedesignprojectwhichisthesubjectofthispaperoriginatedfromareal-worldapplication.AprototypeofamicroscopeslidedryerhadbeendevelopedaroundanOmegaTMmodelCN-390temperaturecontroller,andtheobjectivewastodevelopacustomtemperaturecontrolsystemtoreplacetheOmegasystem.Themotivationwasthatacustomcontrollertargetedspecificallyfortheapplicationshouldbeabletoachievethesamefunctionalityatamuchlowercost,astheOmegasystemisunnecessarilyversatileandequippedtohandleawidevarietyofapplications.ThemechanicallayoutoftheslidedryerprototypeisshowninFigure1.Themainelementofthedryerisalarge,insulated,air-filledchamberinwhichmicroscopeslides,eachwithatissuesampleencasedinparaffin,canbesetoncaddies.Inorderthattheparaffinmaintaintheproperconsistency,thetemperatureintheslidechambermustbemaintainedatadesired(constant)temperature.Asecondchamber(theelectronicsenclosure)housesaresistiveheaterandthetemperaturecontroller,andafanmountedontheendofthedryerblowsairacrosstheheater,carryingheatintotheslidechamber.Thisdesignprojectwascarriedoutduringacademicyear1996-97byfourstudentsundertheauthor 'ssupervisionasaSeniorDesignprojectinDepartmentofEngineeringScienceatTrinityUniversity.Thepurposeofthispaperis-Electronicsenclosure4.5'1SlideChamber4.5'1SlideChamber10.2SMTopViewtodescribetheproblemandthestudents solutioninsomedetail,andtodiscusssomeofthpedagogicalopportunitiesofferedbyaninterdisciplinarydesignprojectofthistype.Thestudents'ownreportwaspresentedatthe199i0rlNAtConferenceonUndergraduateResearch[1].Section2givesamoredetailedstatementoftheproblem,includingperformaneespecifications,andSection3describesthestudents 'design.Section4makesupthebpaper,anddiscussesinsomedetailseveralaspectsofthedesignprocesswhichofferuniquepedagogicalopportunities.Finally,Section5offerssomeconclusions.ProblemStatementThebasicideaoftheprojectistoreplacetherelevantpartsofthefunctionalityofanOmegaCN-390temperaturecontrollerusingacustom-designedsystem.Theapplicationdictatesthattemperaturesettingsareusuallykeptconstantforlongperiodsoftime,butit 'importantthatstepchangesbetrackedina “reasonable”manrequirehmerttsemaiboildowntoallowingachambertemperatureset-pointtobeentered,displayingbothset-pointandactualtemperatures,andtrackingstepchangesinset-pointtemperaturewithacceptablerisetime,steady-stateerror,andovershoot.

TableLTemperamrecontroHerspecificadott^Set-poiuttemperatureentryRansePrecision60-99°C1°CSet-point(einpemtuiedisplayRanse?60-99°CPrecision1°CChmnbertemperaturedisplayRaime60-99°CPiecision1°CAccuracy*±1°CChambertemperaturestepresponseRange(steadystate)60-99°CAccuracy(steadystate)土1°CMaxiiiunno^^eTshoot1°CSettlingtime(to土1c，C)120sAlthoughnotexplicitlyapartofthespecificationsinTable1,itwasclearthatthecustomerdesireddigitaldisplaysofset-pointandactualtemperatures,andthatset-pointtemperatureentryshouldbedigitalaswell(asopposedto,say,throughapotentiometersetting).SystemDesignTherequirementsfordigitaltemperaturedisplaysandsetpointentryaloneareenoughtodictatethatamicrocontrollerbaseddesignislikelythemostappropriate.Figure2showsablockdiagramofthestudents'design.Themicrocontroller,aMotorolaMC68HC705B16(6805forshort),istheheartofthesystem.Itacceptsinputsfromasimplefour-keykeypadwhichallowspecificationoftheset-pointtemperature,anditdisplaysbothset-pointandmeasuredchambertemperaturesusingtwo-digitseven-segmentLEDdisplayscontrolledbyadisplaydriver.Alltheseinputsandoutputsareaccommodatedbyparallelportsonthe6805.Chambertemperatureissensedusingapre-calibratedthermistorandinputviaoneofthe6805 alog-to-digit'lsnputs.Finally,apulse-widthmodulation(PWM)outputonthe6805isusedtodrivearelaywhichswitcheslinepowertotheresistiveheateroffandon.Figure3showsamoredetailedschematicoftheelectronicsandtheirinterfacingtothe6805.Thekeypad,aStorm3K041103,hasfourkeyswhichareinterfacedtopinsPA0{PA3ofPortA,configuredasinputs.Onekeyfunctionsasamodeswitch.Twomodesaresupported:setmodeandrunmode.Insetmodetwooftheotherkeysareusedtospecifytheset-pointtemperature:oneincrementsitandonedecrements.Thefourthkeyisunusedatpresent.TheLEDdisplaysaredrivenbyaHarrisSemiconductorICM7212displaydriverinterfacedtopinsPB0{PB6ofPortB,configuredasoutputs.Thetemperature-sensingthermistordrives,throughavoltagedivider,pinAN0(oneofeightanaloginputs).Finally,pinPLMA(oneoftwoPWMoutputs)drivestheheaterrelay.

Softwareonthe6805implementsthetemperaturecontrolalgorithm,maintainsthetemperaturedisplays,andalterstheset-pointinresponsetokeypadinputs.Becauseitisnotcompleteatthiswriting,softwarewillnotbediscussedindetailinthispaper.Thecontrolalgorithminparticularhasnotbeendetermined,butitislikelytobeasimpleproportionalcontrollerandcertainlynotmorecomplexthanaPID.SomecontroldesignissueswillbediscussedinSection4,however.TheDesignProcessAlthoughessentiallytheprojectisjusttobuildathermostat,itpresentsmanynicepedagogicalopportunities.Theknowledgeandexperieneebaseofaseniorengineeringundergraduatearejustenoughtobringhimorhertothebrinkofasolutiontovariousaspectsoftheproblem.Yet,ineachcase,realworldconsiderationscomplicatethesituationsignificantly.Fortunatelythesecomplicationsarenotinsurmountable,andtheresultisaverybeneficialdesignexperienee.Theremainderofthissectionlooksatafewaspectsoftheproblemwhichpresentthetypeoflearningopportunityjustdescribed.Section4.1discussessomeofthefeaturesofasimplifiedmathematicalmodelofthethermalpropertiesofthesystemandhowitcanbe

easilyvalidatedexperimentally.Section4.2describeshowrealisticcontrolalgorithmdesignscanbearrivedatusingintroductoryconceptsincontroldesign.Section4.3pointsoutsomeimportantdeficienciesofsuchasimplifiedmodeling/controldesignprocessandhowtheycanbeovercomethroughsimulation.Finally,Section4.4givesanoverviewofsomeofthemicrocontroller-relateddesignissueswhichariseandlearningopportunitiesoffered.MathematicalModelLumped-elementthermalsystemsaredescribedinalmostanyintroductorylinearcontrolsystemstext,andjustthissortofmodelisapplicabletotheslidedryerproblem.Figure4showsasecond-orderlumped-elementthermalmodeloftheslidedryer.ThestatevariablesarethetemperaturesTaoftheairintheboxandTboftheboxitself.Theinputstothesystemarethepoweroutputq(t)oftheheaterandtheambienttemperatureTmaandmbare劭emassesoftheairandthebox,respectively,andCaandCbtheirspecificheats^and超areheattransfercoefficientsfromtheairtotheboxandfromtheboxtotheexternalworld,respectively."1（爲(wèi)"1（爲(wèi)一爲(wèi)）"2（爲(wèi)Figure4.Limiped-eleinent/JiernialmodelIt'nothardtoshowthatthe(linearized)stateequationscorrespondingtoFigure4areTOC\o"1-5"\h\z\o"CurrentDocument""切Crl—“l(fā)(爲(wèi)一兀｝ (1)"烙— “1(爲(wèi)—爲(wèi))—(鬲—7^) ⑵TakingLaplacetransformsof(1)and(2)andsolvingforTa(s),whichistheoutputofinterest,givesthefollowingopen-loopmodelofthethermalsystem:A⑸ A(5)whereKisaconstantandD(s)isasecond-orderpolynomial.K,tz,andthecoefficientsofD(s)arefunctionsofthevariousparametersappearingin(1)and(2).Ofcoursethevariousparametersin(1)and(2)arecompletelyunknown,butit 'snothaedckesh(fthat,regtheirvalues,D(s)hastworealzeros.Thereforethemaintransferfunctionofinterest(whichis

theonefromQ(S),sincewe'IIassumeconstantambienttemperature)canbewritten爲(wèi)⑸_K(Z+l)C>(5)—1)(02$+1)Moreover,it'sooohardtoshowthat1=tp1<1=tz<1=tp2,i.e.,thatthezeroliesbetweenthetwopoles.Bothoftheseareexcellentexercisesforthestudent,andtheresultistheopenlooppole-zerodiagramofFigure5.illll———x e 狄 Re一1/。2—1/G-1/。1Figure￡P(guān)ole-zerodiagrcmiofGaq(s)Obtainingacompletethermalmodel,then,isreducedtoidentifyingtheconstantKandthethreeunknowntimeconstantsin(3).Fourunknownparametersisquiteafew,butsimpleexperimentsshowthat1=tp1_1=tz;1=tp2sothattz;tp2_0aregoodapproximations.Thustheopen-loopsystemisessentiallyfirst-orderandcanthereforebewrittenKGM)一越 ⑷(wherethesubscriptp1hasbeendropped).Simpleopen-loopstepresponseexperimentsshowthat,forawiderangeofinitialtemperaturesandheatinputs,K_0:14_=Wandt_295s.1ControlSystemDesignUsingthefirst-ordermodelof(4)fortheopen-looptransferfunctionGaq(s)andassumingforthemomentthatlinearcontroloftheheaterpoweroutputq(t)ispossible,theblockdiagramofFigure6representstheclosed-loopsystem.Td(s)isthedesired,orset-point,temperature,C(s)isthecompensatortransferfunction,andQ(s)istheheateroutputinwatts.

Giventhissimplesituation,introductorylinearcontroldesigntoolssuchastherootlocusmethodcanbeusedtoarriveataC(s)whichmeetsthestepresponserequirementsonrisetime,steady-stateerror,andovershootspecifiedinTable1.Theupshot,ofcourse,isthataproportionalcontrollerwithsufficientgaincanmeetallspecifications.Overshootisimpossible,andincreasinggainsdecreasesbothsteady-stateerrorandrisetime.Unfortunately,sufficientgaintomeetthespecificationsmayrequirelargerheatoutputsthantheheateriscapableofproducing.Thiswasindeedthecaseforthissystem,andtheresultisthattherisetimespecificationcannotbemet.Itisquiterevealingtothestudenthowusefulsuchanoversimplifiedmodel,carefullyarrivedat,canbeindeterminingoverallperformaneelimitations.SimulationModelGrossperformanceanditslimitationscanbedeterminedusingthesimplifiedmodelofFigure6,butthereareanumberofotheraspectsoftheclosed-loopsystemwhoseeffectsonperformancearenotsosimplymodeled.Chiefamongthesearequantizationerrorinanalog-to-digitalconversionofthemeasuredtemperatureand-theuseofPWMtocontroltheheater.Bothofthesearenonlinearandtime-varyingeffects,andtheonlypracticalwaytostudythemisthroughsimulation(orexperiment,ofcourse).Figure7showsaSimulinkTMblockdiagramoftheclosed-loopsystemwhichincorporatestheseeffects.A/DconverterquantizationandsaturationaremodeledusingstandardSimulinkquantizerandsaturationblocks.ModelingPWMismorecomplicatedandrequiresacustomS-functiontorepresentit.□—SuhCCH"D&rE3Zff0137□—SuhCCH"D&rE3Zff0137pFigure*Siita/lhikblockdiagramofclosed^loopsystetnThissimulationmodelhasprovenparticularlyusefulingaugingtheeffectsofvaryingthebasicPWMparametersandhenceselectingthemappropriately.(I.e.,theIongertheperiod,thelargerthetemperatureerrorPWMintroduces.Ontheotherhand,alongperiodisdesirabletoavoidexcessiverelay “chatter,”amongotherthings.)PWMisoftendifficultforstudentstogandthesimulationmodelallowsanexplorationofitsoperationandeffectswhichisquiterevealing.TheMicrocontrollerSimpleclosed-loopcontrol,keypadreading,anddisplaycontrolaresomeoftheclassicapplicationsofmicrocontrollers,andthisprojectincorporatesallthree.Itisthereforeanexcellentall-aroundexerciseinmicrocontrollerapplications.Inaddition,becausetheprojectistoproduceanactualpackagedprtotype,itwon'tdotouseasimpleevaluationboardwiththeI/Opinsjumperedtothetargetsystem.Instead,it 'snecessarytodevelopacompleteapplication.Thisentailsthechoiceofanappropriatepartfromthebroadrangeofferedinatypicalmicrocontrollerfamilyandlearningtouseafairlysophisticateddevelopmentenvironment.Finally,acustomprinted-circuitboardforthemicrocontrollerandperipheralsmustbedesignedandfabricated.MicrocontrollerSelection」nviewofexistinglocalexpertise,theMotorolalineofmicrocontrollerswaschosenforthisproject.Still,thisdoesnotnarrowthechoicedownmuch.Afairlydisciplinedstudyofsystemrequirementsisnecessarytospecifywhichmicrocontroller,outofscoresofvariants,isrequiredforthejob.Thisisdifficultforstudents,astheygenerallylacktheexperieneeandintuitionneededaswellastheperseveraneetowadethroughmanufacturersselectionguides.Partoftheproblemisinchoosingmethodsforinterfacingthevariousperipherals(e.g.,whatkindofdisplaydrivershouldbeused?).AstudyofrelevantMotorolaapplicationnotes[2,3,4]provedveryhelpfulinunderstandingwhatbasicapproachesareavailable,andwhatmicrocontroller/peripheralcombinationsshouldbeconsidered.TheMC68HC705B16wasfinallychosenonthebasisofitsavailableA/DinputsandPWMoutputsaswellas24digitalI/Olines.Inretrospectthisisprobablyoverkill,asonlyoneA/Dchannel,onePWMchannel,and11I/Opinsareactuallyrequired(seeFigure3).Thedecisionwasmadetoerronthesafesidebecauseacompletedevelopmentsystemspecifictothechosenpartwasnecessary,andtheprojectbudgetdidnotpermitasecondsuchsystemtobepurchasedshouldthefirstproveinadequate.MicrocontrollerApplicationDevelopmentBreadboardingoftheperipheralhardware,developmentofmicrocontrollersoftware,andfinaldebuggingandtestingofacustomprinted-circuitboardforthemicrocontrollerandperipheralsallrequireadevelopmentenvironmentofsomekind.Thechoiceofadevelopmentenvironment,likethatofthemicrocontrolleritself,canbebewilderingandrequiressomefacultyexpertise.Motorolamakesthreegradesofdevelopmentenvironmentrangingfromsimpleevaluationboards(ataround$100)tofull-blownreal-timein-circuitemulators(atmorelike$7500).Themiddleoptionwaschosenforthisproject:theMMEVS,whichconsistsof_aplatformboard(whichsupportsall6805-familyparts),_anemulatormodule(specifictoB-seriesparts),and_acableandtargetheadadapter(package-specific).Overall,thesystemcostsabout$900andprovides,withsomelimitations,in-circuitemulationcapability.ItalsocomeswiththesimplebutsufficientsoftwaredevelopmentenvironmentRAPID[5].Studentsfindlearningtousethistypeofsystemchallenging,buttheexperiencetheygaininreal-worldmicrocontrollerapplicationdevelopmentgreatlyexceedsthetypicalfirst-courseexperienceusingsimpleevaluationboards.Printed-CircuitBoard.Thelayoutofasimple(thoughdefinitelynottrivial)printed-circuitboardisanotherpracticallearningopportunitypresentedbythisproject.Thefinalboardlayout,withpackageoutlines,isshown(at50%ofactualsize)inFigure8.Therelativesimplicityofthecircuitmakesmanualplacementandroutingpractical-infact,itlikelygivesbetterresultsthanautomaticinanapplicationlikethis-andthestudentisthereforeexposedtofundamentalissuesofprinted-circuitlayoutandbasicdesignrules.Thelayoutsoftwareusedwastheverynicepackagepcb,2andtheboardwasfabricatedin-housewiththeaidofourstaffelectronicstechnician.Figure&Printed-circuitlayoutforBncrocontwllerboard中文翻譯:單片機(jī)溫度控制：一個(gè)跨學(xué)科的本科生工程設(shè)計(jì)項(xiàng)目JamesS.McDonald工程科學(xué)系三一大學(xué)德克薩斯州圣安東尼奧市78212摘要：本文所描述的是作者領(lǐng)導(dǎo)由四個(gè)三一大學(xué)高年級(jí)學(xué)生組成的團(tuán)隊(duì)進(jìn)行的一個(gè)跨學(xué)科工程項(xiàng)目的設(shè)計(jì)。該項(xiàng)目的目標(biāo)是設(shè)計(jì)一個(gè)氣室內(nèi)溫度控制系統(tǒng)。該系統(tǒng)的要求是：當(dāng)實(shí)際氣室的溫度階躍響應(yīng)時(shí)，規(guī)定范圍內(nèi)的溫度進(jìn)入氣室后，穩(wěn)定時(shí)的溫度誤差和超調(diào)量必須少于一個(gè)絕對(duì)溫度。本組學(xué)生開(kāi)發(fā)設(shè)計(jì)是基于摩托羅拉 MC68HC0系列單片機(jī)。該問(wèn)題的教學(xué)價(jià)值也通過(guò)某些步驟的關(guān)鍵描述在本文說(shuō)明。研究結(jié)果表明，解決該方案需要具有廣泛的工程學(xué)科知識(shí)，包括相關(guān)電子、機(jī)械和控制系統(tǒng)工程的知識(shí)。1引言該設(shè)計(jì)項(xiàng)目來(lái)自一個(gè)實(shí)際應(yīng)用問(wèn)題，一個(gè)關(guān)于顯微鏡載玻片干燥劑溫控器一一歐米茄CN-390溫度控制器，而這個(gè)設(shè)計(jì)的目標(biāo)是研發(fā)一個(gè)自定義的通用溫度控制系統(tǒng)取代歐米茄系統(tǒng)、一個(gè)以更低的成本實(shí)現(xiàn)相同功能的自定義控制器，就像歐米茄系統(tǒng)一樣，并不需要能夠全方位的處理各種問(wèn)題。該載玻片干燥機(jī)的機(jī)械布局如圖1所示。干燥機(jī)的主體是一個(gè)足夠大的絕緣充氣室，里面依次存放著薄紙包著的石蠟。為了使石蠟保持適當(dāng)穩(wěn)定性，載玻片氣室的溫度必須維持穩(wěn)定。第二個(gè)氣筒（電子圍繞元件）設(shè)有一個(gè)電阻加熱器、一個(gè)溫度控制器以及一個(gè)安裝在干燥機(jī)上的風(fēng)扇，是為了把風(fēng)吹過(guò)加熱器，把熱量帶到載玻片氣室。自1996-97學(xué)年來(lái)，本文作者帶領(lǐng)四位三一大學(xué)工程科學(xué)系的高年級(jí)學(xué)生開(kāi)展此項(xiàng)目的研究。本文的目的說(shuō)明了提出一些問(wèn)題并詳細(xì)闡述學(xué)生的一些解決方案，而且討論了這種類型的跨學(xué)科設(shè)計(jì)項(xiàng)目在教學(xué)方面應(yīng)用的問(wèn)題。這份學(xué)生報(bào)告曾經(jīng)在 1997年全國(guó)本科畢業(yè)生研討會(huì)上提出過(guò)并討論過(guò)。第2節(jié)給出該設(shè)計(jì)的更多詳細(xì)情況，包括性能規(guī)格。第3節(jié)具體學(xué)生的設(shè)計(jì)。第4節(jié)是論文的主體，討論該設(shè)計(jì)在教學(xué)應(yīng)用方面的實(shí)施問(wèn)題。最后，第5節(jié)全文總結(jié)。2問(wèn)題闡述該項(xiàng)目基本的思想是設(shè)計(jì)一個(gè)自定義溫度控制系統(tǒng)來(lái)取代相關(guān)的歐米茄 CN-390溫度控制器。溫度時(shí)通常保持在一個(gè)穩(wěn)定的常數(shù)，但重要的是階躍變化可以被“合理”的跟蹤。因此主要要求如下：?可以對(duì)空氣室的溫度進(jìn)行設(shè)定，?同時(shí)顯示設(shè)定值和實(shí)際溫度，?以及在設(shè)定溫度值情況下，可接受范圍內(nèi)的跟蹤階躍變化，穩(wěn)態(tài)誤差，超調(diào)量。設(shè)定溫度接口設(shè)定溫度顯示室內(nèi)溫度顯示范圍精度準(zhǔn)確度60-991°C±1°C室內(nèi)溫度階梯響應(yīng)范圍（穩(wěn)定狀態(tài)）精度（穩(wěn)定狀態(tài)）最大超調(diào)設(shè)定時(shí)間（到土1°）60-99±1°C1°C120s表1 精確的規(guī)格說(shuō)明盡管表1部分說(shuō)明并不明確，但是它清楚的反映了人們對(duì)數(shù)字顯示器在設(shè)定值和實(shí)際溫度的要求和溫度應(yīng)該通過(guò)數(shù)值輸入來(lái)設(shè)定（而不是，通過(guò)電位器設(shè)置） 。3.系統(tǒng)設(shè)計(jì)根據(jù)微控設(shè)計(jì)，數(shù)字溫度顯示和單點(diǎn)輸入的要求可能是最合適的。圖 2為學(xué)生的設(shè)計(jì)框圖。

摩托羅拉MC68HC705B16簡(jiǎn)稱6805）,是系統(tǒng)的核心。它通過(guò)一個(gè)簡(jiǎn)單的4鍵小鍵盤(pán)對(duì)溫度進(jìn)行設(shè)定，同時(shí)使用兩個(gè)顯示驅(qū)動(dòng)控制7段LED數(shù)碼管來(lái)顯示定值和氣室溫度的測(cè)量值。所有這些，輸入和輸出信號(hào)與6805的并行口相連。氣室的溫度值使用預(yù)校準(zhǔn)熱敏電阻測(cè)量，并通過(guò)6805的數(shù)模轉(zhuǎn)換輸入。最后，6085的脈沖寬度調(diào)制（PWM輸出用來(lái)驅(qū)動(dòng)一個(gè)繼電器，以控制線性電阻加熱器的閉合和斷開(kāi)。圖3更詳細(xì)的顯示了6805的接口和電子器件。使用暴風(fēng)3K041103型號(hào)四鍵鍵盤(pán)，通過(guò)PA0-PA3端口進(jìn)行數(shù)據(jù)輸入。其中一個(gè)重要的功能是進(jìn)行模式切換。兩種模式：固定模式和運(yùn)行模式。在固定模式下，其他兩個(gè)鍵用于設(shè)定溫度，一個(gè)增加，一個(gè)減少，第四個(gè)按鍵暫無(wú)作用。LED顯示屏由哈里斯半導(dǎo)體ICM7212進(jìn)行驅(qū)動(dòng)，通過(guò)PB0-PB6端口與芯片相連，作為輸出。熱敏電阻由電壓分頻器驅(qū)動(dòng)，通過(guò) AN0針腳（八個(gè)模擬輸入端口中的一個(gè)）相連。最后,PLMA十腳（兩個(gè)PWM輸出端口中的一個(gè)）驅(qū)動(dòng)加熱繼電器。個(gè)）相連。最后,圖3單片機(jī)原理圖是關(guān)于用軟件實(shí)現(xiàn)溫度控制算法、保持溫度顯示以及改變鍵盤(pán)輸入響應(yīng)，這將不會(huì)在本文詳細(xì)討論，因?yàn)檫@并不是本文的重點(diǎn)，也沒(méi)有編譯完成。軟件部分還沒(méi)有確定控制算法，但很可能是一個(gè)簡(jiǎn)單的比例控制，比 PID算法簡(jiǎn)單。一些控制設(shè)計(jì)的問(wèn)題將在第四節(jié)討論。4設(shè)計(jì)過(guò)程雖然該項(xiàng)目的本質(zhì)是建立一個(gè)恒溫器，但它有許多很好的契機(jī)可以供教學(xué)借鑒。高級(jí)工程本科教育的知識(shí)只是能夠讓學(xué)生們具有解決問(wèn)題的能力。然而，很多情況下，實(shí)際情況卻和理論有些不同。不過(guò)，這些不是問(wèn)題，參與這個(gè)項(xiàng)目的設(shè)計(jì)，將獲得很多設(shè)計(jì)方面的寶貴經(jīng)驗(yàn)。本節(jié)的其余部分著眼于其他的幾個(gè)方面： 4.1節(jié)討論系統(tǒng)的一些特征，簡(jiǎn)化系統(tǒng)熱性能的數(shù)學(xué)模型，以及一些簡(jiǎn)單理論的證明。 4.2節(jié)介紹確定實(shí)際控制算法。4.3節(jié)指出控制設(shè)計(jì)程序的一些不足，并通過(guò)模擬環(huán)境，指出怎樣克服問(wèn)題。 4.4節(jié)給出單片機(jī)的一些設(shè)計(jì)相關(guān)概述，以及出現(xiàn)問(wèn)題和值得借鑒之處。4.1數(shù)學(xué)模型集總元件熱系統(tǒng)符合線性控制，適用于載玻片干燥機(jī)的問(wèn)題。圖4顯示了二階集總元件熱量模型的載玻片干燥機(jī)。狀態(tài)變量是溫度，Ta是箱內(nèi)空氣的溫度，Tb是箱子本身的溫度。該系統(tǒng)輸入功率等于q（t）的熱量和環(huán)境溫度T的和。mamb分別對(duì)應(yīng)空氣和箱子的質(zhì)量。Ca和Cb則分別是其對(duì)應(yīng)熱量。ml和m2分別是空氣與箱子間以及箱子與外界間的傳熱系圖4-1 集總元件熱模型由圖4可以推出（線性）狀態(tài)方程"bCrt?—“1（爲(wèi)一耳） （1）"烙QjN—“1（爲(wèi)—爲(wèi)）—（昂—九） ⑵拉普拉斯變換⑴和⑵等式，并整理Ta（s）。有趣的是，可以推出一個(gè)開(kāi)環(huán)的熱系統(tǒng)方程。

其中K是一個(gè)常數(shù)，D(s)是一個(gè)二階的多項(xiàng)式。K,tz,以及系數(shù)D(s)和在⑴和(2)等式中出現(xiàn)的系數(shù)功能相近。當(dāng)然，在(1)和(2)等式中各種參數(shù)在未知的情況下，不難證明D(s)與其他參數(shù)的值無(wú)關(guān)，具有