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1、Introduction of Thermistor,Alip Chen March 15 2011,Concept,Definition: Thermistor: thermally sensitive resistor Application: Temperature Detector, Control, Switch, Fuse Catalog: NTC,PTC, RTD, NTC: Negative Temperature Coefficient Resistor PTC: Positive Temperature Coefficient Resistor RTD: Resistanc

2、e Temperature Detector,Resistance Temperature Detector,Type: Wire Wound, Thin Film Material: Pt, Cu, Ni Principle: R- T effect Sample: see photos Typical performance: See below table Features: accuracy, linear,Resistance Temperature Detector,Resistance Temperature Detector (Rtd) vs. Thermocouples (G

3、eneral Principles),Thermocouple,Type: K, E, J, N ,B, R, S Material: Pt Rhodium, W- Rhenium, Constantan, Cupron Principle: Seebeck effect that the junction between two metals generates a voltage which is a function of temperature Typical performance: See below table Features: interchangeable, wide ra

4、nge of temperatures,Type J : V (mV) / T (C) Table,NTC,Type: disc, rod, chip Material: Ceramic (Mn, Fe, Co, Ni, Zn etc, transition metal oxides) Principle: R-T effect Samples: See photo: Epoxy and Glass PKG. Typical performance: See below table Features: Cheap, high sensitivity, small size,NTC,Parame

5、ter Zero-Power Resistance (R0) : R0 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 () (Tempera

6、ture coefficient): Alpha, a material characteristic, 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

7、 as a material constant and that indicates the relationship of material resistivity to temperature.,NTC,Steinhart Equation (R-T Relationship) Experiential Formula: , ,,NTC,Parameter Tolerance : Tolerance for thermistor is the specified resistance percentage or temperature deviation from curv

8、e nominal values. Thermal Time Constant: It is the time required for a thermistor 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 powe

9、r required to raise the thermistors body temperature by 1C in a particular measurement 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）,NTC,Stability and Reliability: Form BetaTherm sensor,NTC,Example used for AWG,PTC,Type: disc, rod, Material: Ceramic (BaTiO3, SrTiO3, PbTiO3,) Principle: R-T effect, Courier effect Application: Switch and heater, Protection, Features:,Summary,