基于单片机的温度控制外文文献及中文翻译.docx

基于单片机的温度控制外文文献及中文翻译.docx

《基于单片机的温度控制外文文献及中文翻译.docx》由会员分享，可在线阅读，更多相关《基于单片机的温度控制外文文献及中文翻译.docx（29页珍藏版）》请在冰豆网上搜索。

基于单片机的温度控制外文文献及中文翻译

TemperatureControlUsingaMicrocontroller:

AnInterdisciplinaryUndergraduateEngineeringDesignProject

JamesS.McDonald

DepartmentofEngineeringScience

TrinityUniversity

SanAntonio,TX78212

Abstract：

Thispaperdescribesaninterdisciplinarydesignprojectwhichwasdoneunderthe

author'ssupervisionbyagroupoffourseniorstudentsintheDepartmentofEngineeringScience

atTrinityUniversity.Theobjectiveoftheprojectwastodevelopatemperaturecontrolsystem

foranair-filledchamber.Thesystemwastoallowentryofadesiredchambertemperatureina

prescribedrangeandtoexhibitovershootandsteady-statetemperatureerroroflessthan1degree

Kelvinintheactualchambertemperaturestepresponse.Thedetailsofthedesigndevelopedby

thisgroupofstudents,basedonaMotorolaMC68HC05familymicrocontroller,aredescribed.

Thepedagogicalvalueoftheproblemisalsodiscussedthroughadescriptionofsomeofthekey

stepsinthedesignprocess.Itisshownthatthesolutionrequiresbroadknowledgedrawnfrom

severalengineeringdisciplinesincludingelectrical,mechanical,andcontrolsystems

engineering.

1Introduction

Thedesignprojectwhichisthesubjectofthispaperoriginatedfromareal-worldapplication.

AprototypeofamicroscopeslidedryerhadbeendevelopedaroundanOmegaTMmodel

CN-390temperaturecontroller,andtheobjectivewastodevelopacustomtemperaturecontrol

systemtoreplacetheOmegasystem.Themotivationwasthatacustomcontrollertargeted

specificallyfortheapplicationshouldbeabletoachievethesamefunctionalityatamuchlower

cost,astheOmegasystemisunnecessarilyversatileandequippedtohandleawidevarietyof

applications.

ThemechanicallayoutoftheslidedryerprototypeisshowninFigure1.Themainelement

ofthedryerisalarge,insulated,air-filledchamberinwhichmicroscopeslides,eachwitha

tissuesampleencasedinparaffin,canbesetoncaddies.Inorderthattheparaffinmaintainthe

properconsistency,thetemperatureintheslidechambermustbemaintainedatadesired

（constant）temperature.Asecondchamber（theelectronicsenclosure）housesaresistiveheater

andthetemperaturecontroller,andafanmountedontheendofthedryerblowsairacrossthe

heater,carryingheatintotheslidechamber.Thisdesignprojectwascarriedoutduringacademic

year1996–97byfourstudentsundertheauthor'ssupervisionasaSeniorDesignprojectinthe

DepartmentofEngineeringScienceatTrinityUniversity.Thepurposeofthispaperis

todescribetheproblemandthestudents'solutioninsomedetail,andtodiscusssomeofthe

pedagogicalopportunitiesofferedbyaninterdisciplinarydesignprojectofthistype.The

students'ownreportwaspresentedatthe1997NationalConferenceonUndergraduateResearch

[1].Section2givesamoredetailedstatementoftheproblem,includingperformance

specifications,andSection3describesthestudents'design.Section4makesupthebulkofthe

paper,anddiscussesinsomedetailseveralaspectsofthedesignprocesswhichofferunique

pedagogicalopportunities.Finally,Section5offerssomeconclusions.

2ProblemStatement

ThebasicideaoftheprojectistoreplacetherelevantpartsofthefunctionalityofanOmega

CN-390temperaturecontrollerusingacustom-designedsystem.Theapplicationdictatesthat

temperaturesettingsareusuallykeptconstantforlongperiodsoftime,butit'snonetheless

importantthatstepchangesbetrackedina“reasonable”manner.Thusthemainrequirements

boildownto

·allowingachambertemperatureset-pointtobeentered,

·displayingbothset-pointandactualtemperatures,and

·trackingstepchangesinset-pointtemperaturewithacceptablerisetime,steady-stateerror,

andovershoot.

AlthoughnotexplicitlyapartofthespecificationsinTable1,itwasclearthatthecustomer

desireddigitaldisplaysofset-pointandactualtemperatures,andthatset-pointtemperatureentry

shouldbedigitalaswell（asopposedto,say,throughapotentiometersetting）.

3SystemDesign

Therequirementsfordigitaltemperaturedisplaysandsetpointentryaloneareenoughto

dictatethatamicrocontrollerbaseddesignislikelythemostappropriate.Figure2showsablock

diagramofthestudents'design.

Themicrocontroller,aMotorolaMC68HC705B16（6805forshort）,istheheartofthesystem.

Itacceptsinputsfromasimplefour-keykeypadwhichallowspecificationoftheset-point

temperature,anditdisplaysbothset-pointandmeasuredchambertemperaturesusingtwo-digit

seven-segmentLEDdisplayscontrolledbyadisplaydriver.Alltheseinputsandoutputsare

accommodatedbyparallelportsonthe6805.Chambertemperatureissensedusinga

pre-calibratedthermistorandinputviaoneofthe6805'sanalog-to-digitalinputs.Finally,a

pulse-widthmodulation（PWM）outputonthe6805isusedtodrivearelaywhichswitchesline

powertotheresistiveheateroffandon.

Figure3showsamoredetailedschematicoftheelectronicsandtheirinterfacingtothe6805.

Thekeypad,aStorm3K041103,hasfourkeyswhichareinterfacedtopinsPA0{PA3ofPortA,

configuredasinputs.Onekeyfunctionsasamodeswitch.Twomodesaresupported:

setmode

andrunmode.Insetmodetwooftheotherkeysareusedtospecifytheset-pointtemperature:

oneincrementsitandonedecrements.Thefourthkeyisunusedatpresent.TheLEDdisplaysare

drivenbyaHarrisSemiconductorICM7212displaydriverinterfacedtopinsPB0{PB6ofPortB,

configuredasoutputs.Thetemperature-sensingthermistordrives,throughavoltagedivider,pin

AN0（oneofeightanaloginputs）.Finally,pinPLMA（oneoftwoPWMoutputs）drivesthe

heaterrelay.

Softwareonthe6805implementsthetemperaturecontrolalgorithm,maintainsthe

temperaturedisplays,andalterstheset-pointinresponsetokeypadinputs.Becauseitisnot

completeatthiswriting,softwarewillnotbediscussedindetailinthispaper.Thecontrol

algorithminparticularhasnotbeendetermined,butitislikelytobeasimpleproportional

controllerandcertainlynotmorecomplexthanaPID.Somecontroldesignissueswillbe

discussedinSection4,however.

4TheDesignProcess

Althoughessentiallytheprojectisjusttobuildathermostat,itpresentsmanynice

pedagogicalopportunities.Theknowledgeandexperiencebaseofaseniorengineering

undergraduatearejustenoughtobringhimorhertothebrinkofasolutiontovariousaspectsof

theproblem.Yet,ineachcase,realworldconsiderationscomplicatethesituationsignificantly.

Fortunatelythesecomplicationsarenotinsurmountable,andtheresultisaverybeneficial

designexperience.Theremainderofthissectionlooksatafewaspectsoftheproblemwhich

presentthetypeoflearningopportunityjustdescribed.Section4.1discussessomeofthefeatures

ofasimplifiedmathematicalmodelofthethermalpropertiesofthesystemandhowitcanbe

easilyvalidatedexperimentally.Section4.2describeshowrealisticcontrolalgorithmdesignscan

bearrivedatusingintroductoryconceptsincontroldesign.Section4.3pointsoutsome

importantdeficienciesofsuchasimplifiedmodeling/controldesignprocessandhowtheycanbe

overcomethroughsimulation.Finally,Section4.4givesanoverviewofsomeofthe

microcontroller-relateddesignissueswhichariseandlearningopportunitiesoffered.

4.1MathematicalModel

Lumped-elementthermalsystemsaredescribedinalmostanyintroductorylinearcontrolsystems

text,andjustthissortofmodelisapplicabletotheslidedryerproblem.Figure4showsa

second-orderlumped-elementthermalmodeloftheslidedryer.Thestatevariablesarethe

temperaturesTaoftheairintheboxandTboftheboxitself.Theinputstothesystemarethe

poweroutputq（t）oftheheaterandtheambienttemperatureT￥.maandmbarethemassesofthe

airandthebox,respectively,andCaandCbtheirspecificheats.μ1andμ2areheattransfer

coefficientsfromtheairtotheboxandfromtheboxtotheexternalworld,respectively.

It'snothardtoshowthatthe（linearized）stateequationscorrespondingtoFigure4are

TakingLaplacetransformsof

（1）and

（2）andsolvingforTa（s）,whichistheoutputof

interest,givesthefollowingopen-loopmodelofthethermalsystem:

whereKisaconstantandD（s）isasecond-orderpolynomial.K,tz,andthecoefficientsof

D（s）arefunctionsofthevariousparametersappearingin

（1）and

（2）.Ofcoursethevarious

parametersin

（1）and

（2）arecompletelyunknown,butit'snothardtoshowthat,regardlessof

theirvalues,D（s）hastworealzeros.Thereforethemaintransferfunctionofinterest（whichis

theonefromQ（s）,sincewe'llassumeconstantambienttemperature）canbewritten

Moreover,it'snottoohardtoshowthat1=tp1<1=tz<1=tp2,i.e.,thatthezeroliesbetween

thetwopoles.Bothoftheseareexcellentexercisesforthestudent,andtheresultistheopenloop

pole-zerodiagramofFigure5.

Obtainingacompletethermalmodel,then,isreducedtoidentifyingtheconstantKandthe

threeunknowntimeconstantsin（3）.Fourunknownparametersisquiteafew,butsimple

experimentsshowthat1=tp1_1=tz;1=tp2sothattz;tp2_0aregoodapproximations.Thusthe

open-loopsystemisessentiallyfirst-orderandcanthereforebewritten

（wherethesubscriptp1hasbeendropped）.

Simpleopen-loopstepresponseexperimentsshowthat,forawiderangeofinitial

temperaturesandheatinputs,K_0:

14_=Wandt_295s.1

4.2ControlSystemDesign