檢測(cè)技術(shù)與過(guò)控-熱電偶溫度計(jì)

傳感器與檢測(cè)基礎(chǔ)FundamentalsofSensorsandTemperatur Measuremen 溫度測(cè)Slide

TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度Itisbasedontheelectricalandthermaltransportpropertiesofdifferentmetals.Whenatemperaturedifferentialismaintainedacrossagivenmetal,thevibrationofatomsandmotionofelectronsisaffectedsothatadifferenceinpotentialexistsacrossthematerial.兩種不同成份的均質(zhì)導(dǎo)體組成閉合回路，當(dāng)兩端存在溫差時(shí)，回路中會(huì)有電流通過(guò)，即存在熱電勢(shì)。熱電勢(shì)包括溫差電勢(shì)和接觸電勢(shì)Slide TemperatureMeasuremenThermoelectric sorsThermocouples)熱電偶溫度Threeeffectsareassociatedwiththermocouples.TheyareasPeltiereffect.Itstatesthatifacurrentflowsthroughathermocoupleonejunctionisheated(putsoutenergy)andtheotherjunctioniscooled(absorbsenergy).Thompsoneffect.Itstatesthatwhenacurrentflowsinaconductoralongwhichthereisatemperaturedifference,heatisproducedorabsorbed,dependinguponthedirectionofthecurrentandthevariationofSlide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度Temperaturedifferencepotential（溫差電勢(shì)， Thompsoneffect）Itstatesthatwhenacurrentflowsinaconductoralongwhichthereisatemperaturedifference,heatisproducedorabsorbed,dependinguponthedirectionofthecurrentandthevariationoftemperature.同一導(dǎo)體:兩端溫度 勢(shì)Slide

σA—導(dǎo)體的 只與導(dǎo)體材料和兩端溫度t、t0有關(guān),與導(dǎo)體長(zhǎng)度、截面大小、若兩導(dǎo)體材料一定，僅與兩端溫差有

TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度 帖Itstatesthatifacurrentflowsthroughathermocoupleonejunctionisheated(putsoutenergy)andtheotherjunctioniscooled(absorbsenergy).兩種電子密度不同的導(dǎo)體相接觸電勢(shì)Slide

k e—單位電荷NA、NB—溫度為t時(shí)，A、B導(dǎo)體的電子密度；t—接觸點(diǎn)的溫度。大小取決于兩導(dǎo)體材料及接觸點(diǎn)溫度，當(dāng)材料一定時(shí)只與接觸點(diǎn)溫度有關(guān)。若兩導(dǎo)體材料一定，僅與其接點(diǎn)溫度有關(guān) ↑→AB↑ TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度設(shè)電子密度A導(dǎo)體>B導(dǎo)體;溫度t>t0，則回路中總電勢(shì)為EEAB(t,t0)eAB(t)eA(t,t0eAB(t0)eB(t,t0因溫差電勢(shì)<<接觸電勢(shì),Slide

EAB(t,t0

)eAB(t)eAB(t0

TemperatureMeasuremThermoelectric sorsThermocouples)熱電偶溫度小結(jié)EAB(t,t0)取決于兩種材料及兩端溫度,與導(dǎo)體粗細(xì)長(zhǎng)短及沿長(zhǎng)度上的溫度分布情況無(wú)關(guān)。材料選定,且固定冷端溫度t0，測(cè)得EAB(t,t0)tEAB(t0,t0)=0；EAB(t,t0)腳標(biāo)AB為熱電勢(shì)方向，A為正極，Bt為高溫端，t0為低溫端。若次序改變，則熱電勢(shì)前面符號(hào)也隨之改變EEAB(t,t0)EBA(t,t0)EAB(t0,tEEAB(t,t0)EAB(t,t1)EAB(t1,t0Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度熱電偶基本定律（Lawsfor（一）中間導(dǎo)體定在熱電偶回路在熱電偶回路接入第三種導(dǎo)體C，只要與第三種導(dǎo)體C相接的兩接點(diǎn)溫度相同，則對(duì)回路中電勢(shì)無(wú)影響。Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度ABAB0A0Slide

同理可證圖(b，總熱電勢(shì)仍為EAB(t,t0根據(jù)該定律，可在回路中方便連TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度熱電偶基本定律（Lawsfor（一）中間導(dǎo)體定Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度熱電偶基本定律（Lawsfor（一）中間導(dǎo)體定Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度（二）均質(zhì)導(dǎo)體定由一種均質(zhì)導(dǎo)體組成的閉合回路，無(wú)論導(dǎo)體截面、長(zhǎng)度以及各處溫度分布如何，均不產(chǎn)生熱電勢(shì)定律說(shuō)明：若兩熱電極分別由定律說(shuō)明：若兩熱電極分別由兩種均質(zhì)導(dǎo)體組成，則熱電勢(shì)僅與兩接點(diǎn)溫度有關(guān)，與沿?zé)犭姌O的溫度分布無(wú)關(guān)根據(jù)該定律，可衡量熱電極材料的均勻Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度（三）中間溫度定若連接點(diǎn)溫度為若連接點(diǎn)溫度為tn，連接導(dǎo)體Aˊ、Bˊ的熱電特性與A、B相同，則總電勢(shì)等于熱電偶與連接導(dǎo)體的熱電勢(shì)的代數(shù)和。 0)=EAB(t,tn)+ 根據(jù)該定律，可延伸加長(zhǎng)熱電Slide TemperatureMeasuremen1.Thermoelectric sorsThermocouples)熱電偶溫度（三）中間溫度定Slide TemperatureMeasuremen 1.Thermoelectric sors （四）標(biāo)準(zhǔn)電極定導(dǎo)體A、B分別與導(dǎo)體C組成熱電偶，測(cè)量端溫度均為t，參考端均為t0，EEAB(t,t0)=EAC(t,t0)-EBC(t,t0)=EAC(t,t0)+ECB導(dǎo)體C稱(chēng)為標(biāo)準(zhǔn)電極，一般采用純鉑材料Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)（一）標(biāo)準(zhǔn)化熱電鉑銠10—Platinum-rhodium

分度號(hào)測(cè)溫范圍測(cè)溫范圍0～1400℃，短期鉑銠13— 分度號(hào)熱電勢(shì)比熱電勢(shì)比S熱電偶大15%左右，其它性能幾乎相同測(cè)溫范圍：同S，誤差±(1±0.25%t）℃鉑銠30--鉑銠 分度號(hào)高溫?zé)岣邷責(zé)犭娕肌?～1600℃，短期1800℃冷端在40℃以下使用時(shí)，一般不需進(jìn)行冷端溫度補(bǔ)Slide TTemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)鎳鉻--Chromel-

分度號(hào)測(cè)溫范圍測(cè)溫范圍-50～1000℃，短期鎳鉻 分度號(hào):測(cè)測(cè)溫范圍-200～750℃，短期靈敏度最高，價(jià)廉；濕度較大時(shí)較其它熱偶耐腐蝕熱電勢(shì)大。500℃：37mV銅 熱電偶（分度號(hào)廉價(jià)金屬熱電偶中精確度最高，穩(wěn)定性好，低溫測(cè)量靈敏度高-200～300℃，短期350℃。誤差±0.5～1℃Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)鐵 熱電偶（分度號(hào)700℃700℃以下線(xiàn)性非常好-40～700℃，短期750℃，誤差±1.5～2.5℃鎳鉻硅—鎳硅熱電偶（分度號(hào)13001300℃以下，高溫抗氧化能力強(qiáng)，穩(wěn)定性及復(fù)現(xiàn)性好，耐核輻射及耐低溫性能好。-200～1200℃，短期1300℃。誤差±1.5～2.5℃。有取代廉價(jià)金屬熱電偶與部分替代S熱電偶的趨勢(shì)。鎢錸系列熱電鎢錸5—鎢錸26熱電 分度號(hào)：WRe5-WRe26鎢錸3—鎢錸25熱電 分度號(hào)：WRe3-WRe25用于用于1600℃以上測(cè)量。上限達(dá)2800℃，最好2000℃以下誤差±1%t℃Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)標(biāo)準(zhǔn)化熱電偶的熱電特性曲線(xiàn)（參考端Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)Certainstandardconfigurationsofthermocouplesusingspecificmetals(oralloysofmetals)havebeenadoptedandgivenletterdesignations.Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)Slide TemperatureMeasuremen2.2.Thermocoupletypes（熱電偶種類(lèi)ThetypeJandKthermocouplesarenotedfortheirratherlargeslope,thatis,highsensitivity—makingmeasurementseasierforagivenchangeintemperature.ThetypeSthermocouplehasmuchlessslopeandislesssensitive.Ithasthesignificantadvantagesofamuchlargerpossiblerangeofmeasurement,includingveryhightemperature,andishighlyinertmaterial.Thesecurvesarenotexactlylinear.Totakeadvantageoftheinherentaccuracypossiblewiththesedevices,comprehensivetablesofvoltageversustemperaturehavebeendeterminedformanytypesofthermocouples.(Thermocoupletables，Slide

熱電偶分度表

2.Thermocoupletypes（熱電偶種類(lèi)TemperatureMeasu2.Thermocoupletypes（熱電偶種類(lèi)（二）非標(biāo)準(zhǔn)化熱電（（1）鎳鉻—金鐵熱電偶(NiCr-用于0～273K，誤差±0.5℃，低溫?zé)犭娕际蓟仧犭娕迹–-TiC熱電勢(shì)遠(yuǎn)大于金屬熱電偶 高,復(fù)石墨—碳化鈦熱電偶（C-TiC含碳?xì)夥?、中性氣氛中可測(cè)2000℃硅化鎢—二硅化鉬熱電偶（WSi2—MoSi2） 碳化硼—石墨熱電偶（B4C- 600～2000℃范圍內(nèi)線(xiàn)性好，熱電勢(shì)大，為鎢錸熱電偶的19倍，最適宜作控制信號(hào)。Slide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)Athermocouplebyitself,ofcourse,simplyaweldedoreventwistedjunctionbetweentwometals.Therearecases,however,wheretheTCissheathed（的）inaprotectivecovering（防護(hù)層）orevensealedinglasstoprotecttheunitfromahostileenvironment.Slide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)熱電極

長(zhǎng)度由安裝條件 深度而定一般350～2000mm絕緣子

保護(hù)套管：有金屬、非金屬和金屬陶瓷三接線(xiàn)盒

用于導(dǎo)線(xiàn)與熱電極連Slide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)常用連接方螺紋連接或法蘭連接，用于P<10MPa的測(cè)固定螺紋錐形保護(hù)管連高強(qiáng)度結(jié)構(gòu)，用于P<30MPa、流速<80m/sSlide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)鎧裝熱電偶Armored標(biāo)準(zhǔn)鎧裝Slide

特點(diǎn)及適用動(dòng)態(tài)特性好，鎧裝型τ≤10s，使用溫度低 短

TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)Thethermocoupletemperaturesensorhasthegreatestrangeofallthetypesconsidered.Ingeneral,typeJthermocoupleisusablefrom-150℃to745℃,whilethetypeSisusableupto1765℃.TimeThethermocoupletimeresponseissimplyrelatedtothesizeofthewireandanyprotectivematerialusedwiththesensor.ThetimeresponseequatestohowlongittakesfortheTCsystemtoreachthermalequilibriumwiththe10s-20s;10-Slide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)即：厚壁粗偶的大鎧裝熱電特點(diǎn) 兼有鎧裝和普通熱電偶的優(yōu)點(diǎn)Slide TemperatureMeasuremen3.3.ConstructionofThermocouples（熱電偶結(jié)構(gòu)薄膜熱電

薄膜工藝（真空蒸鍍、化學(xué)涂覆等測(cè)溫范圍：-200℃-Slide TemperatureMeasuremen Thermocoupletables（熱電偶分度表EAB(TT0)取決于兩導(dǎo)體材料及接T、T0有關(guān)。則EAB(T,T0)T(測(cè)量端或熱端)溫度有關(guān)。即:Slide TemperatureMeasuremen Thermocoupletables（熱電偶分度表分度表：T0=0℃時(shí)，熱電勢(shì)E(T,0)與溫度TSlide

TE(T,0)，E(T,→

TemperatureMeasuremen Thermocoupletables（熱電偶分度表Thethermocoupletablessimplygivethevoltageforaparticulartypeofthermocouplewhenthereferencejunctionsareataparticularreferencetemperature,andthemeasurementjunctionisatatemperatureofinterest.TwoSlide TemperatureMeasuremen Thermocoupletables（熱電偶分度表Inmostcases,themeasuredvoltagedoesnotfallexactlyonatablevalue.Whenthishappens,itisnecessarytointerpolatebetweentablevaluesthatbracketthedesiredvalue.Ingeneral,thevalueoftemperaturecanbefoundusingthefollowinginterpolationequation:Themeasuredvoltageliesbetweenahighervoltageandalowervoltage,whichareintables.Slide TemperatureMeasuremen Thermocoupletables（熱電偶分度表ItispossibletousethesetableswithaTCthathasadifferentreferencetemperaturebyanappropriateshiftinthetable.Ifanewreferenceisgreaterthanthetablereference,allvoltagesofthetablewillbelessforthisTC.Theamountlesswillbejustthevoltageofthenewreferenceasfoundonthetable.（中間溫度定律）ThechangeofthereferenceneedstobenotedwhenusingTCinrealSlide TemperatureMeasuremen Thermocoupletables（熱電偶分度表ConsideratypeJthermocouplewitha30℃reference.ThetableshowsthatatypeJthermocouplewitha0℃referenceproduces1.54mVat30℃.Thisisthecorrectionfactorthatwillbeappliedtoanyvoltageexpectedwhenthereferenceis30℃.Slide TemperatureMeasuremen55熱電偶需要引入控制EEE(t,t0')EE(t,t0若A′，B′和A，B相同，或者熱電特性相同則滿(mǎn)足要求——補(bǔ)償導(dǎo)線(xiàn)Slide TemperatureMeasuremen55兩種廉價(jià)導(dǎo)體材料制成的導(dǎo)線(xiàn)（在一定溫度范圍內(nèi)熱電特性與所連接的熱電偶相同或十分相近）補(bǔ)償型(C)：材料與熱電偶不相同，用于貴金屬，如B、S延伸型(X):基本采用與熱電偶相同的材料，用于廉價(jià)金屬，如K、E等Slide TemperatureMeasuremen55Page使用注意型號(hào)匹配與僅起到冷端延伸作用，一般要求補(bǔ)償導(dǎo)線(xiàn)與熱電偶的連接點(diǎn)的溫度不超過(guò)Slide TemperatureMeasuremen6.6.Referencecompensation（冷端補(bǔ)償、冷端處理分度表是在t0＝0℃得現(xiàn)在：冷端溫度不是0，需要處Aproblemwiththepracticaluseofthermocouplesisthenecessityofknowingthereferencetemperature.（參考端溫度）BecausetheTCvoltageisdirectlyrelatedtothedifferencebetweenthemeasurementandreferencejunctiontemperatures（測(cè)量端和參考端溫度差）,variationsofthereferencetemperatureshowupasdirecterrorsinthemeasurementtemperaturedetermination.Slide TemperatureMeasuremen6.6.Referencecompensation（冷端補(bǔ)償、冷端處理冰點(diǎn)冷端延伸到冰水混合物EAB(t,0)查表求得tSlide TemperatureMeasuremen6.6.Referencecompensation（冷端補(bǔ)償、冷端處理計(jì)算當(dāng)t0≠0℃，測(cè)得的回路熱電勢(shì)為E(t，t0)，由熱電偶回路測(cè)得E(t0,0)—冷端0℃，測(cè)量端t0℃時(shí)的熱電勢(shì)即冷端溫度校正值。由室溫計(jì)測(cè)得t0℃，查分度表得到。適用 或臨時(shí)性測(cè)Slide TemperatureMeasuremen6.6.Referencecompensation（冷端補(bǔ)償、冷端處理①A′,B′②A′,B′③A′,B′補(bǔ)償導(dǎo)線(xiàn)，接反了例：①A′,B′②A′,B′③A′,B′補(bǔ)償導(dǎo)線(xiàn)，接反了表電勢(shì)E＝E