外文翻译供热站温度实时监测Word格式文档下载.docx

外文翻译供热站温度实时监测Word格式文档下载.docx

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Thermistorsareinexpensive,easily-obtainabletemperaturesensors.Theyareeasytouseandadaptable.Circuitswiththermistorscanhavereasonableoutoutvoltages-notthemillivoltoutputsthermocoupleshave.Becauseofthesequalities,thermistorsarewidelyusedforsimpletemperaturemeasurements.They'

renotusedforhightemperatures,butinthetemperaturerangeswheretheyworktheyarewidelyused.Thermistorsaretemperaturesensitiveresistors.Allresistorsvarywithtemperature,butthermistorsareconstructedofsemiconductormaterialwitharesistivitythatisespeciallysensitivetotemperature.However,unlikemostotherresistivedevices,theresistanceofathermistordecreaseswithincreasingtemperature.That'

sduetothepropertiesofthesemiconductormaterialthatthethermistorismadefrom.Forsome,thatmaybecounterintuitive,butitiscorrect.Hereisagraphofresistanceasafunctionoftemperatureforatypicalthermistor.Noticehowtheresistancedropsfrom100kW,toaverysmallvalueinarangearoundroomtemperature.Notonlyistheresistancechangeintheoppositedirectionfromwhatyouexpect,butthemagnitudeofthepercentageresistancechangeissubstantial.

TemperatureSensor-TheThermocoupleYouareat:

Elements-Sensors-ThermocouplesReturntoTableofContentsAthermocoupleisajunctionformedfromtwodissimilarmetals.Actually,itisapairofjunctions.Oneatareferencetemperature（like0oC）andtheotherjunctionatthetemperaturetobemeasured.Atemperaturedifferencewillcauseavoltagetobedevelopedthatistemperaturedependent.（ThatvoltageiscausedbysomethingcalledtheSeebeckeffect.）Thermocouplesarewidelyusedfortemperaturemeasurementbecausetheyareinexpensive,ruggedandreliable,andtheycanbeusedoverawidetemperaturerange.Inparticular,othertemperaturesensors（likethermistorsandLM35sensors）areusefularoundroomtemperature,butthethermocouplecanTheThermocoupleWhyUsethermocouplesToMeasureTemperature?

Theyareinexpensive.Theyareruggedandreliable.Theycanbeusedoverawidetemperaturerange.WhatDoesAThermocoupleLookLike?

Hereitis.Notethetwowires（oftwodifferentmetals）joinedinthejunction.Whatdoesathermocoupledo?

Howdoesitwork?

Thejunctionoftwodissimilarmetalsproducesatemperaturedependentvoltage.Forabetterdescriptionofhowitworks,clickhere.HowDoYouUseAThermocouple?

Youmeasurethevoltagethethermocoupleproduces,andconvertthatvoltagetoatemperaturereading.Itmaybebesttodotheconversiondigitallybecausetheconversioncanbefairlynonlinear.ThingsYouNeedToKnowAboutThermocouplesAjunctionbetweentwodissimilarmetalsproducesavoltage.Inthethermocouple,thesensingjunction-producesavoltagethatdependsupontemperature.Wherethethermocoupleconnectstoinstrumentation-copperwires?

-youhavetwomorejunctionsandtheyalsoproduceatemperaturedependentvoltage.Thosejunctionsareshowninsidetheyellowoval.Whenyouuseathermocouple,youneedtoensurethattheconnectionsareatsomestandardtemperature,oryouneedtouseanelectronicallycompensatedsystemthattakesthosevoltagesintoaccount.Ifyourthermocoupleisconnectedtoadataacquisitionsystem,thenchancesaregoodthatyouhaveanelectronicallycompensatedsystem.Onceweobtainareadingfromavoltmeter,themeasuredvoltagehastobeconvertedtotemperature.Thetemperatureisusuallyexpressedasapolynomialfunctionofthemeasuredvoltage.Sometimesitispossibletogetadecentlinearapproximationoveralimitedtemperaturerange.Therearetwowaystoconvertthemeasuredvoltagetoatemperaturereading.Measurethevoltageandlettheoperatordothecalculations.Usethemeasuredvoltageasaninputtoaconversioncircuit-eitheranalogordigital.Letuslookatsomeothertypesofbase-metalthermocouples.TypeTthermocouplesarewidelyusedasaretypeKandTypeN.TypeK（Ni-Cr/Ni-Al）thermocouplesarealsowidelyusedintheindustry.Ithashighthermopowerandgoodresistancetooxidation.TheoperatingtemperaturerangeofaTypeKthermocoupleisfrom-269oCto+1260oC.However,thisthermocoupleperformsratherpoorlyinreducingatmospheres.TypeT（Cu/Cu-Ni）thermocouplescanbeusedinoxidizingofinertatmospheresoverthetemperaturerangeof-250oCto+850oC.Inreducingormildlyoxidizingenvironments,itispossibletousethethermocoupleuptonearly+1000oC.TypeN（Nicrosil/Nisil）thermocouplesaredesignedtobeusedinindustrialenvironmentsoftemperaturesupto+1200oC.Apolynomialequationusedtoconvertthermocouplevoltagetotemperature（oC）overawiderangeoftemperatures.Wecanwritethepolynomialas:

Thecoefficients,anaretabulatedinmanyplaces.HerearetheNBSpolynomialcoefficientsforatypeKthermocouple.（Source:

T.J.Quinn,Temperature,AcademicPressInc.,1990）TypeKPolynomialCoefficientsnan00.226584602124152.10900267233.424832210340.6824-860963914.954.83506x10106-1.18452x101271.38690x10138-6.33708x1013WhatIfTheSurroundingTemperatureExceedsLimits?

Therearereallynothermocouplesthatcanwithstandoxidizingatmospheresfortemperaturesabovetheupperlimitoftheplatinum-rhodiumtypethermocouples.Wecannot,therefore,measuretemperatureinsuchhightemperatureconditions.Otheroptionsformeasuringextremelyhightemperaturesareradiationorthenoisepyrometer.Fornon-oxidizingatmospheres,tungsten-rheniumbasedthermocouplesshowsgoodperformanceupto+2750oC.Theycanbeused,forashortperiod,intemperaturesupto+3000oC.Theselectionofthetypesofthermocoupleusedforlowtemperaturesensingisprimarilybasedonmaterialsofathermocouple.Inaddition,thermopoweratlowtemperatueisratherlow,someasurementofEMFwillbeproportionallysmallaswell.MoreFactsOnVariousThermocoupleTypesAvarietyofthermocouplestodaycoverarangeoftemperaturefrom-250oCto+3000oC.Thedifferenttypesofthermocouplearegivenletterdesignations:

B,E,J,K,R,S,TandNTypesR,SandBarenoblemetalthermocouplesthatareusedtomeasurehightemperature.Withintheirtemperaturerange,theycanoperateforalongerperiodoftimeunderanoxidizingenvironment.TypeSandtypeRthermocouplesaremadeupofplatinum（Pt）andrhodium（Rh）mixedindifferentratios.AspecificPt/Rhratioisusedbecauseitleadstomorestableandreproduciblemeasurements.TypesSandRhaveanuppertemperaturelimitof+1200oCinoxidizingatmospheres,assumingawirediameterof0.5mm.TypeSandtypeRthermocouplesaremadeupofplatinum（Pt）andrhodium（Rh）mixedindifferentratios.AspecificPt/Rhratioisusedbecauseitleadstomorestableandreproduciblemeasurements.TypesSandRhaveanuppertemperaturelimitof+1200oCinoxidizingatmospheres,assumingawirediameterof0.5mm.TypeBthermocoupleshaveadifferentPt/RhratiothanTypeSandR.Ithasanuppertemperaturelimitof+1750oCinoxidizingatmospheres.Duetoanincreasedamountofrhodiumcontent,typeBthermocouplesarenoquitesostableaseithertheTypeRorTypeS.TypesE,J,K,T,andNarebase-metalthermocouplesthatareusedforsensinglowertemperatures.Theycannotbeusedforsensinghightemperaturesbecauseoftheirrelativelylowmeltingpointandslowerfailureduetooxidation.TypeBthermocoupleshaveadifferentPt/RhratiothanTypeSandR.Ithasanuppertemperaturelimitof+1750oCinoxidizingatmospheres.Duetoanincreasedamountofrhodiumcontent,typeBthermocouplesarenoquitesostableaseithertheTypeRorTypeS.wewilllookintosomedifferencesbetweendifferentbase-metalthermocouples.TypeE（Ni-Cr/Cu-Ni）thermocoupleshaveanoperatingtemperaturerangefrom-250oCto+800oC.Theiruseislesswidespreadthanotherbase-metalthermocouplesduetoitslowoperatingtemperature.However,measurementsmadebyaTypeEhaveasmallermarginoferror.1000hoursofoperationinairofaTypeEthermocoupleat+760oC,having3mmwires,sholdnotleadtoachangeinEMFequivalenttomorethan+1oC.TypeJ（Fe/Cu-Ni）thermocouplesarewidelyusedinindustryduetotheirhighthermopowerandlowcost.Thistypeofthermocouplehasanoperatingtemperaturerangefrom0oCto+760oC.LinkstoRelatedLessonsTemperatureSensorsThermistorsThermocouplesLM35sOtherSensorsStrainGagesTemperatureSensorLaboratoriesReturntoTableofContents

ExperimentsWithTemperatureSensors-DataGatheringMeasuringtemperatureisthemostcommonmeasurementtask.Therearenumerousdevicesavailableformeasuringtemperature.Manyofthemarebuiltusingoneofthesecommonsensors.ThermistorThermocoupleLM35IntegratedCircuitTemperatureSensorYoucangetmoreinformationaboutthesesensorsbyclickingthelinksabove.LaboratoryThepurposeofthislaboratoryistogettimeresponsedataforthethreesensorsyouwereintroducedtolabsweek.HerearelinkstoLabVIEWprogramsyoucanuse.NTempsHydra.vi-tomeasuretemperaturefromtheHydra.NVoltsHydra.vi-tomeasurevoltagefromtheHydra.ResetHydra.vi-A"

sub-vi"

youneedtoresettheHydra.1Temp.vi-Asub-vithatwilltakeonetemperaturemeasurementontheHydra.1VoltHydra.vi-Asub-vithatwilltakeonevoltagemeasurementontheHydra.Youshouldhaveallthefilesaboveonyourdesktop.Youcanclickoneachlinkandsavetothedesktop,oryoucanfindtheNMeasfolderinmypublicspaceandcopytheentirefoldertothedesktop（best）.YouonlyneedtodoubleclicktheNTempsorNVoltsfilestostartandruntheminLabVIEW-buttheyhavetobetakenoutofthenetworkfolder!

Onceyouhavethefilestogetherina