单片机温度控制英文文献及翻译.docx
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单片机温度控制英文文献及翻译.docx
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单片机温度控制英文文献及翻译
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AnInterdisciplinaryUndergraduateEngineeringDesignProjectJamesS.McDonaldDepartmentofEngineeringScienceTrinityUniversitySanAntonio,TX78212AbstractThispaperdescribesaninterdisciplinarydesignprojectwhichwasdoneundertheauthor’ssupervisionbyagroupoffourseniorstudentsintheDepartmentofEngineeringScienceatTrinityUniversity.Theobjectiveoftheprojectwastodevelopatemperaturecontrol
systemforanair-filled
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TemperatureControlUsingaMicrocontroller:
AnInterdisciplinaryUndergraduateEngineeringDesignProject
JamesS.McDonald
DepartmentofEngineeringScience
TrinityUniversity
SanAntonio,TX78212
Abstract
Thispaperdescribesaninterdisciplinarydesignprojectwhichwasdoneundertheauthor’s
supervisionbyagroupoffourseniorstudentsintheDepartmentofEngineeringScienceat
TrinityUniversity.Theobjectiveoftheprojectwastodevelopatemperaturecontrolsystemfor
anair-filledchamber.Thesystemwastoallowentryofadesiredchambertemperatureina
prescribedrangeandtoexhibitovershootandsteady-statetemperatureerroroflessthan1degree
Kelvinintheactualchambertemperaturestepresponse.Thedetailsofthedesigndevelopedby
thisgroupofstudents,basedonaMotorolaMC68HC05familymicrocontroller,aredescribed.
Thepedagogicalvalueoftheproblemisalsodiscussedthroughadescriptionofsomeofthekey
stepsinthedesignprocess.Itisshownthatthesolutionrequiresbroadknowledgedrawnfrom
severalengineeringdisciplinesincludingelectrical,mechanical,andcontrolsystems
engineering.
1Introduction
Thedesignprojectwhichisthesubjectofthispaperoriginatedfromareal-world
application.AprototypeofamicroscopeslidedryerhadbeendevelopedaroundanOmegaTM
modelCN-390temperaturecontroller,andtheobjectivewastodevelopacustomtemperature
controlsystemtoreplacetheOmegasystem.Themotivationwasthatacustomcontroller
targetedspecificallyfortheapplicationshouldbeabletoachievethesamefunctionalityata
muchlowercost,astheOmegasystemisunnecessarilyversatileandequippedtohandleawide
varietyofapplications.
ThemechanicallayoutoftheslidedryerprototypeisshowninFigure1.Themainelement
ofthedryerisalarge,insulated,air-filledchamberinwhichmicroscopeslides,eachwitha
tissuesampleencasedinparaffin,canbesetoncaddies.Inorderthattheparaffinmaintainthe
properconsistency,thetemperatureintheslidechambermustbemaintainedatadesired
(constant)temperature.Asecondchamber(theelectronicsenclosure)housesaresistiveheater
andthetemperaturecontroller,andafanmountedontheendofthedryerblowsairacrossthe
heater,carryingheatintotheslidechamber.Thisdesignprojectwascarriedoutduringacademic
1year1996–97byfourstudentsundertheauthor’ssupervisionasaSeniorDesignprojectinthe
DepartmentofEngineeringScienceatTrinityUniversity.Thepurposeofthispaperis
todescribetheproblemandthestudents’solutioninsomedetail,andtodiscusssomeofthe
pedagogicalopportunitiesofferedbyaninterdisciplinarydesignprojectofthistype.The
students’ownreportwaspresentedatthe1997NationalConferenceonUndergraduateResearch
[1].Section2givesamoredetailedstatementoftheproblem,includingperformance
specifications,andSection3describesthestudents’design.Section4makesupthebulkofthe
paper,anddiscussesinsomedetailseveralaspectsofthedesignprocesswhichofferunique
pedagogicalopportunities.Finally,Section5offerssomeconclusions.
2ProblemStatement
ThebasicideaoftheprojectistoreplacetherelevantpartsofthefunctionalityofanOmegaCN-
390temperaturecontrollerusingacustom-designedsystem.Theapplicationdictatesthat
temperaturesettingsareusuallykeptconstantforlongperiodsoftime,butit’snonetheless
importantthatstepchangesbetrackedina“reasonable”manner.Thusthemainrequirements
boildownto
·allowingachambertemperatureset-pointtobeentered,
·displayingbothset-pointandactualtemperatures,and
·trackingstepchangesinset-pointtemperaturewithacceptablerisetime,steady-stateerror,
andovershoot.
2AlthoughnotexplicitlyapartofthespecificationsinTable1,itwasclearthatthecustomer
desireddigitaldisplaysofset-pointandactualtemperatures,andthatset-pointtemperatureentry
shouldbedigitalaswell(asopposedto,say,throughapotentiometersetting).
3SystemDesign
Therequirementsfordigitaltemperaturedisplaysandsetpointentryaloneareenoughto
dictatethatamicrocontrollerbaseddesignislikelythemostappropriate.Figure2showsablock
diagramofthestudents’design.
3Themicrocontroller,aMotorolaMC68HC705B16(6805forshort),istheheartofthe
system.Itacceptsinputsfromasimplefour-keykeypadwhichallowspecificationoftheset-
pointtemperature,anditdisplaysbothset-pointandmeasuredchambertemperaturesusingtwo-
digitseven-segmentLEDdisplayscontrolledbyadisplaydriver.Alltheseinputsandoutputsare
accommodatedbyparallelportsonthe6805.Chambertemperatureissensedusingapre-
calibratedthermistorandinputviaoneofthe6805’sanalog-to-digitalinputs.Finally,apulse-
widthmodulation(PWM)outputonthe6805isusedtodrivearelaywhichswitcheslinepower
totheresistiveheateroffandon.
Figure3showsamoredetailedschematicoftheelectronicsandtheirinterfacingtothe
6805.Thekeypad,aStorm3K041103,hasfourkeyswhichareinterfacedtopinsPA0{PA3of
PortA,configuredasinputs.Onekeyfunctionsasamodeswitch.Twomodesaresupported:
set
modeandrunmode.Insetmodetwooftheotherkeysareusedtospecifytheset-point
temperature:
oneincrementsitandonedecrements.Thefourthkeyisunusedatpresent.The
LEDdisplaysaredrivenbyaHarrisSemiconductorICM7212displaydriverinterfacedtopins
PB0{PB6ofPortB,configuredasoutputs.Thetemperature-sensingthermistordrives,througha
voltagedivider,pinAN0(oneofeightanaloginputs).Finally,pinPLMA(oneoftwoPWM
outputs)drivestheheaterrelay.
4Softwareonthe6805implementsthetemperaturecontrolalgorithm,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
5easilyvalidatedexperimentally.Section4.2describeshowrealisticcontrolalgorithmdesignscan
bearrivedatusingintroductoryconceptsincontroldesign.Section4.3pointsoutsome
importantdeficienciesofsuchasimplifiedmodeling/controldesignprocessandhowtheycanbe
overcomethroughsimulation.Finally,Section4.4givesanoverviewofsomeofthe
microcontroller-relateddesignissueswhichariseandlearningopportunitiesoffered.
4.1MathematicalModel
Lumped-elementthermalsystemsaredescribedinalmostanyintroductorylinearcontrolsystems
text,andjustthissortofmodelisapplicabletotheslidedryerproblem.Figure4showsasecond-
orderlumped-elementthermalmodeloftheslidedryer.Thestatevariablesarethetemperatures
TaoftheairintheboxandTboftheboxitself.Theinputstothesystemarethepoweroutput
q(t)oftheheaterandtheambienttemperatureT¥.maandmbarethemassesoftheairandthe
box,respectively,andCaandCbtheirspecificheats.μ1andμ2areheattransfercoefficients
fromtheairtotheboxandfromtheboxtotheexternalworld,respectively.
It’snothardtoshowthatthe(linearized)stateequationscorrespondingtoFigure4are
TakingLaplacetransformsof
(1)and
(2)andsolvingforTa(s),whichistheoutputof
interest,givesthefollowingopen-loopmodelofthethermalsystem:
whereKis
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