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ID:16358170
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时间:2018-08-09
《毕业设计文献翻译热电偶温度传感器》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
1、ThermocoupleTemperatursensorIntroductiontoThermocouplesThethermocoupleisoneofthesimplestofallsensors.Itconsistsoftwowiresofdissimilarmetalsjoinednearthemeasurementpoint.Theoutputisasmallvoltagemeasuredbetweenthetwowires.Whileappealinglysimpleinconcept,th
2、etheorybehindthethermocoupleissubtle,thebasicsofwhichneedtobeunderstoodforthemosteffectiveuseofthesensor.ThermocoupletheoryAthermocouplecircuithasatleasttwojunctions:themeasurementjunctionandareferencejunction.Typically,thereferencejunctioniscreatedwhere
3、thetwowiresconnecttothemeasuringdevice.Thissecondjunctionitisreallytwojunctions:oneforeachofthetwowires,butbecausetheyareassumedtobeatthesametemperature(isothermal)theyareconsideredasone(thermal)junction.Itisthepointwherethemetalschange-fromthethermocoup
4、lemetalstowhatevermetalsareusedinthemeasuringdevice-typicallycopper.Theoutputvoltageisrelatedtothetemperaturedifferencebetweenthemeasurementandthereferencejunctions.ThisisphenomenaisknownastheSeebeckeffect.(SeetheThermocoupleCalculatortogetafeelforthemag
5、nitudeoftheSeebeckvoltage).TheSeebeckeffectgeneratesasmallvoltagealongthelengthofawire,andisgreatestwherethetemperaturegradientisgreatest.Ifthecircuitisofwireofidenticalmaterial,thentheywillgenerateidenticalbutoppositeSeebeckvoltageswhichwillcancel.Howev
6、er,ifthewiremetalsaredifferenttheSeebeckvoltageswillbedifferentandwillnotcancel.InpracticetheSeebeckvoltageismadeupoftwocomponents:thePeltiervoltagegeneratedatthejunctions,plustheThomsonvoltagegeneratedinthewiresbythetemperaturegradient.ThePeltiervoltage
7、isproportionaltothetemperatureofeachjunctionwhiletheThomsonvoltageisproportionaltothesquareofthetemperaturedifferencebetweenthetwojunctions.ItistheThomsonvoltagethataccountsformostoftheobservedvoltageandnon-linearityinthermocoupleresponse.Eachthermocoupl
8、etypehasitscharacteristicSeebeckvoltagecurve.Thecurveisdependentonthemetals,theirpurity,theirhomogeneityandtheircrystalstructure.Inthecaseofalloys,theratioofconstituentsandtheirdistributioninthewireisalsoimportant.Thesepot
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