毕业设计文献翻译热电偶温度传感器.docx

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1、ThermocoupleTemperatursensorIntroductiontoThermocouplesThethermocoupleisoneofthesimplestofallsensors.Itconsistsoftwowiresofdissimilarmetalsjoinednearthemeasurementpoint.Theoutputisasmallvoltagemeasuredbetweenthetwowires.Whileappealinglysimpleinconcept,thetheorybehindt

2、hethermocoupleissubtle,thebasicsofwhichneedtobeunderstoodforthemosteffectiveuseofthesensor.ThermocoupletheoryAthermocouplecircuithasatleasttwojunctions:themeasurementjunctionandareferencejunction.Typically,thereferencejunctioniscreatedwherethetwowiresconnecttothemeasu

3、ringdevice.Thissecondjunctionitisreallytwojunctions:oneforeachofthetwowires,butbecausetheyareassumedtobeatthesametemperature(isothermal)theyareconsideredasone(thermal)junction.Itisthepointwherethemetalschange-fromthethermocouplemetalstowhatevermetalsareusedinthemeasur

4、ingdevice-typicallycopper.Theoutputvoltageisrelatedtothetemperaturedifferencebetweenthemeasurementandthereferencejunctions.ThisisphenomenaisknownastheSeebeckeffect.(SeetheThermocoupleCalculatortogetafeelforthemagnitudeoftheSeebeckvoltage).TheSeebeckeffectgeneratesasma

5、llvoltagealongthelengthofawire,andisgreatestwherethetemperaturegradientisgreatest.Ifthecircuitisofwireofidenticalmaterial,thentheywillgenerateidenticalbutoppositeSeebeckvoltageswhichwillcancel.However,ifthewiremetalsaredifferenttheSeebeckvoltageswillbedifferentandwill

6、notcancel.InpracticetheSeebeckvoltageismadeupoftwocomponents:thePeltiervoltagegeneratedatthejunctions,plustheThomsonvoltagegeneratedinthewiresbythetemperaturegradient.ThePeltiervoltageisproportionaltothetemperatureofeachjunctionwhiletheThomsonvoltageisproportionaltoth

7、esquareofthetemperaturedifferencebetweenthetwojunctions.ItistheThomsonvoltagethataccountsformostoftheobservedvoltageandnon-linearityinthermocoupleresponse.EachthermocoupletypehasitscharacteristicSeebeckvoltagecurve.Thecurveisdependentonthemetals,theirpurity,theirhomog

8、eneityandtheircrystalstructure.Inthecaseofalloys,theratioofconstituentsandtheirdistributioninthewireisalsoimportant.Thesepot