仪表简介-3(temperature)

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1、溫度儀錶起源:Seedbeck→thermoelectricity.HumphreyDavy→metalsresistivity&temperaturerelationship.50yearslater…….WilliamSiemens→useplatinumastheelementinaresistancethermometer(callPRTD)C.HMeyers(@1932)→HelicalcoilofPlatinumonacrossedmicawedandmountedtheassemblyt

2、heassemblyinsideaglasstube.Verystableelementbutslowthermalresponsetime.溫度儀錶EvansandBurns→bird-cageelementthisconfigurationisstillabittoofragileforindustrialenvironment.Improve:theplatinumwireisbifilarwoundonaglassorceramicbobbin.溫度儀錶ResistanceMeasuremen

3、tMostcommonvalueis100Ω@0℃DIN43760platinumwiretemp.coefficientα=0.00385Ω/Ω/℃Forthe100Ωwirecorrespondto+0.385Ω/℃@0℃Themorechemicallypureplatinumwireα=0.00392Ω/Ω/℃溫度儀錶10/0.385≒26℃….errorWheatstoneBridgeWheatstoneBridgeR1:R2=R3:R4由分壓得知R5兩端等電位，故不會有電流流經R5，R5可

4、為電流計內阻。溫度儀錶3-wirereduceaffectresistance.(A&Bwireimpedanceeffectwillcancel,becauseeachisinanoppositelegofthebridge.Onemoreextensionwirethan3wirebridge.Butpriceup.Extensionwireaffecttemp.reading.溫度儀錶溫度儀錶銅&鎳銅合金溫度儀錶溫度儀錶溫度儀錶溫度儀錶ThermowellType溫度儀錶Thermowellco

5、nstruction:Drilled:整支管加工車成(一體成型)。Closedend:由管體及末端焊接封尾而成(非一體成型)。Builtedup:Udimension超過工廠車床型式之限制時，分別以鑽頭鑽空兩段鐵棒在焊接組合而成。Type:Tapered耐流速較Straight佳。Thermowellmaterial:依FluorStd.well之材質均採用304S.S.CPCStd.則採用316S.S.Stainlesssteel並不能使用於所有流體，需考慮流體腐蝕性。溫度儀錶ThermowellT

6、ype