热敏电阻介绍.ppt

60 µV/°C
Type J : V (mV) / T (C) Table
Deg 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
TCR Tolerance %
1% 1% 1% 0.12% 0.35% 1% 0.35% 1% 0.35% 0.1%
Resistance Temperature Detector
Resistance Temperature Detector (Rtd) vs. Thermocouples (General Principles)
.00427 .00427 .00672 .00385 .00385 .00385 .00391 .00391 .00375 .00392
Base Resistance Tolerance +/0.2% 0.5% 0.5% 0.06% 0.12% 0.5% 0.12% 0.5% 0.12% 0.5%
Features Accuracy Temperature
Range Initial Cost
Sensitivity
Response Time Robustness Reference Junction Long Term Stability
Output
Electrical Noise Resistance
– Thermal Dissipation Constant: It is defined as the power required to raise the
thermistor’s body temperature by 1°C in a particular measurement medium. Its
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:
– Beta value (β): B value can be regarded a quantitative value of thermistor materials that is assigned as a material constant and that indicates the relationship of material resistivity to temperature.
• Catalog: NTC,PTC, RTD,…
– NTC: Negative Temperature Coefficient Resistor – PTC: Positive Temperature Coefficient Resistor – RTD: Resistance Temperature Detector
10 OHMS AT 25C 10 OHMS AT 25C 120 OHMS AT 0C 100 OHMS AT 0C 100 OHMS AT 0C 100 OHMS AT 0C 100 OHMS AT 100 OHMS AT 0C 100 OHMS AT 0C 100 OHMS AT 0C
TCR (Ohm/Ohm/C)
NTC
• Parameter
– 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.
Rtd More Accurate
-200 to 600ºC
More Expensive 1" Typical (other lengths
available) 1 to 7 seconds
Good
Not Required
Excellent
Resistance 0.4 ohm/ohm/ºC
Highly Linear
Introduction of Thermistor
Alip Chen March 15 2019
Concept
• Definition:
– Thermistor: thermally sensitive resistor
• Application:
– Temperature Detector, Control, Switch, Fuse…
10-40 microvolts/ºC, Approximately linear
More susceptible
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 range of temperatures
Summary
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
Less susceptible
Thermocouple Less Accurate -200 to 2000ºC Less Expensive
Point Sensing Only less than 0.1 second Good, Subject to drift
Required
Good. Subject to drift Voltage
– 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.
Type
CB CC NA PA PB PC PE PF PG PH
Element Material
COPPER COPPER NICKEL PLATINUM PLATINUM PLATINUM PLATINUM PLATINUM PLATINUM PLATINUM
Base Resistance (Ohms)
N(Nicrosil / Nisil)
-270 to 1300
R(Platinum / Rhodium) -50 to 1760
S(Platinum / Rhodium) -50 to 1760
T(Copper/Constantan) -270 to 400
sensitivity 10 µV/°C
68 µV/°C 50 µV/°C 41 µV/°C 10 µV/°C 10 µV/°C 10 µV/°C
– Alpha (α) (Temperature 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.
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 1.122 1.225 1.329 1.432
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