Temperature Measurement (Diagram)
1
Temperature Measurement Changes in temperature is considered a sign of illness thermometer Quantities Kelvin = 1/273.16 of the thermodynamic temperature of the triple point of water The triple point is the temp. at which ice-water-vapor are in equilibrium. 273.16K We express this temperature by 273.15 Celsius Most frequent scale in medicine 2 reference points 0 C - freezing point at atmospheric pressure 100 C - boiling point at atmospheric pressure normal body temperature = 37 C Fahrenheit water freezes at 32 F and boils at 212 F 2 categories: contact measurement + contactless measurement Contactless temperature measurement based on detection of electromagnetic infrared radiation emitted by the human body Radiation thermometers are mainly based on absorption of total radiation energy E , that is connected to temperature by Stefan-Boltzmann law T = (E/Ů) ^ (1/4) Contact Thermometric Methods Most frequently used thermometric methods. based on 3 physical phenomena Thermal volume expansion of liquids liquid commonly used is mercury Mercury situated in cylindrical reservoir from which the mercury can expand into a thick- walled capillary Temperature Х: the volume of the mercury expands and rises in the graduated capillary. the greater the reservoir volume, the smaller the capillary diameter, the greater the sensitivity Thermal expansion of metals Bimetallic thermometer uses metals with different expansion coefficients Accuracy of about 1°C the application in medicine is limited Changes in electrical properties of matters Changes in electric resistance of metals Platinum and nickel are most frequently used resistance of these metals increases with temperature linearly Rt = Ro ( 1 + Şt ) R = resistance correspond to t+0 degree C Ş = thermal change coefficient Changes in electric resistance of semiconductors With increasing temp. the free electron density of semiconductors increase rapidly thermistors: Semiconductor components with thermal dependence of resistance R = A × T^ş × e^(B/T) R = R of a thermistor in thermal equilibrium A, B, ş = material constants T = thermodynamic temp Thermally induced voltage Junction of two identical conductors with another conductor having other characteristics, forms two thermoelectric couples, thermocouples Two contacts are held with two different temperatures, a thermoelectric voltage U arises between the junctions U = (Ş2 – Ş1) (t2 – t1) The voltage depends on the temperature difference of thermoelectric coefficients of the metals used Temperature Measurement.mmap - 2005/2/10 - Mu-Hsun (Teresa) Chen
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Transcript of Temperature Measurement (Diagram)
TemperatureMeasurement
Changes in temperature isconsidered a sign of illness thermometer
Quantities
Kelvin
= 1/273.16 of the thermodynamictemperature of the triple point of water
The triple point is the temp. at whichicewatervapor are in equilibrium. 273.16K
We express this temperature by 273.15
Celsius
Most frequent scale in medicine
2 referencepoints
0 C freezing point atatmospheric pressure
100 C boiling point atatmospheric pressure
normal body temperature = 37 C
Fahrenheit
water freezes at 32 F and boils at 212 F2 categories: contact measurement+ contactless measurement
Contactless temperaturemeasurement
based on detection ofelectromagnetic infrared radiationemitted by the human body
Radiation thermometers are mainlybased on absorption of totalradiation energy E , that isconnected to temperature byStefanBoltzmann law
T = (E/ ) ^ (1/4)
ContactThermometricMethods
Most frequently usedthermometric methods.
based on 3physicalphenomena
Thermal volumeexpansion of liquids
liquid commonly used is mercuryMercury situated in cylindrical reservoirfrom which the mercury can expandinto a thick walled capillary
Temperature : the volume of the mercuryexpands and rises in the graduated capillary.
the greater the reservoir volume, the smaller thecapillary diameter, the greater the sensitivity
Thermalexpansionof metals
Bimetallic thermometer
uses metals with different expansion coefficientsAccuracy of about 1°C
the application in medicine is limited
Changes inelectricalpropertiesof matters
Changes inelectricresistanceof metals
Platinum and nickel are most frequently used
resistance of these metals increaseswith temperature linearly
Rt = Ro ( 1 + t )R = resistance correspond to t+0 degree C
= thermal change coefficient
Changes inelectricresistance ofsemiconductors
With increasing temp. the free electrondensity of semiconductors increase rapidly
thermistors: Semiconductor componentswith thermal dependence of resistance
R = A × T^ × e^(B/T)R = R of a thermistor in thermal equilibrium
A, B, = material constants
T = thermodynamic temp
Thermallyinduced voltage
Junction of two identical conductorswith another conductor having othercharacteristics, forms two thermoelectriccouples, thermocouplesTwo contacts are held with two differenttemperatures, a thermoelectricvoltage U arises between the junctions
U = ( 2 – 1) (t2 – t1)The voltage depends on the temperaturedifference of thermoelectriccoefficients of the metals used
Temperature Measurement.mmap 2005/2/10 MuHsun (Teresa) Chen
