《热敏电阻介绍》PPT课件.ppt

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1、Introduction of ThermistorAlip ChenMarch 15 2011ConceptDefinition:Thermistor:thermally sensitive resistor Application:Temperature Detector,Control,Switch,FuseCatalog:NTC,PTC,RTD,NTC:Negative Temperature Coefficient ResistorPTC:Positive Temperature Coefficient ResistorRTD:Resistance Temperature Detec

2、tor Resistance Temperature DetectorType Element Material Base Resistance(Ohms)TCR(Ohm/Ohm/C)Base Resistance Tolerance+/-TCR Tolerance%CB COPPER 10 OHMS AT 25C.00427 0.2%1%CC COPPER 10 OHMS AT 25C.00427 0.5%1%NA NICKEL 120 OHMS AT 0C.00672 0.5%1%PA PLATINUM 100 OHMS AT 0C.00385 0.06%0.12%PB PLATINUM

3、100 OHMS AT 0C.00385 0.12%0.35%PC PLATINUM 100 OHMS AT 0C.00385 0.5%1%PE PLATINUM 100 OHMS AT 0C.00391 0.12%0.35%PF PLATINUM 100 OHMS AT 0C.00391 0.5%1%PG PLATINUM 100 OHMS AT 0C.00375 0.12%0.35%PH PLATINUM 100 OHMS AT 0C.00392 0.5%0.1%Type:Wire Wound,Thin FilmMaterial:Pt,Cu,NiPrinciple:R-T effectSa

4、mple:see photosTypical performance:See below tableFeatures:accuracy,linearResistance Temperature DetectorFeaturesRtdThermocoupleAccuracyMore AccurateLess AccurateTemperature Range-200 to 600C-200 to 2000CInitial CostMore ExpensiveLess ExpensiveSensitivity1 Typical(other lengths available)Point Sensi

5、ng OnlyResponse Time1 to 7 secondsless than 0.1 secondRobustnessGoodGood,Subject to driftReference JunctionNot RequiredRequiredLong Term StabilityExcellentGood.Subject to driftOutputResistance0.4 ohm/ohm/CHighly LinearVoltage10-40 microvolts/C,Approximately linearElectrical NoiseResistanceLess susce

6、ptibleMore susceptibleResistance Temperature Detector(Rtd)vs.Thermocouples(General Principles)ThermocoupleType:K,E,J,N,B,R,SMaterial:Pt Rhodium,W-Rhenium,Constantan,CupronPrinciple:Seebeck effect that the junction between two metals generates a voltage which is a function of temperatureTypical perfo

7、rmance:See below tableFeatures:interchangeable,wide range of temperaturesThermocouple typeOverall range CsensitivityB(Platinum/Rhodium)20 to 182010 V/CE(Chromel/Constantan)-270 to 91068 V/CJ(Iron/Constantan)-210 to 120050 V/CK(Chromel/Alumel)-270 to 137041 V/CN(Nicrosil/Nisil)-270 to 130010 V/CR(Pla

8、tinum/Rhodium)-50 to 176010 V/CS(Platinum/Rhodium)-50 to 176010 V/CT(Copper/Constantan)-270 to 40060 V/CDeg C 0 2 4 6 8-20-0.995-1.093-1.19-1.288-1.385-10-0.501-0.6-0.699-0.798-0.896 0 0-0.101-0.201-0.301-0.401 Deg C 0 2 4 6 8 0 0 0.101 0.202 0.303 0.405 10 0.507 0.609 0.711 0.813 0.916 20 1.019 1.1

9、22 1.225 1.329 1.432 Type J:V(mV)/T(C)TableNTCType:disc,rod,chipMaterial:Ceramic(Mn,Fe,Co,Ni,Zn etc,transition metal oxides)Principle:R-T effectSamples:See photo:Epoxy and Glass PKG.Typical performance:See below tableFeatures:Cheap,high sensitivity,small sizeNTCParameterZero-Power Resistance(R0):R0

10、is the measured DC(direct current)resistance at a specific temperature T when the power dissipation is negligible.Generally consider the power to be negligible when any decrease in power will result in not more than a 0.1%change in resistance.Alpha()(Temperature coefficient):Alpha,a material charact

11、eristic,is defined as the percentage resistance change per degree centigrade.For NTC thermistor,typical value of alpha are in the range of-3%C to-6%C.Beta value():B value can be regarded a quantitative value of thermistor materials that is assigned as a material constant and that indicates the relat

12、ionship of material resistivity to temperature.NTCSteinhart Equation(R-T Relationship)Experiential Formula:,NTCParameterTolerance:Tolerance for thermistor is the specified resistance percentage or temperature deviation from curve nominal values.Thermal Time Constant:It is the time required for a the

13、rmistor to change its body temperature by 63.2%of a specified temperature span when the measurement are made under zero-power conditions in thermally stable environment.Thermal Dissipation Constant:It is defined as the power required to raise the thermistors body temperature by 1C in a particular me

14、asurement medium.Its units is expressed in the unit of mw/C.Rating Power:It is specified as the required power that thermistor are heated up by 100C at 25C.=W/（T-Ta）=I R/（T-Ta）NTCStability and Reliability:Form BetaTherm sensor NTCExample used for AWGPTCType:disc,rod,Material:Ceramic(BaTiO3,SrTiO3,PbTiO3,)Principle:R-T effect,Courier effectApplication:Switch and heater,Protection,Features:Summary