cryogenic thermometry (2)

8/8/2019 Cryogenic Thermometry (2)

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AN OVERVIEW OF CRYOGENIC THERMOMETRY

Karthikeyan SubbuM.Tech (Cryogenic Engineering)

Roll No. 10CR60R11Autumn Semester Seminar-I

Indian Institute Of Technology Kharagpur 1Karthikeyan Subbu


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INTERNATIONAL TE MP ERATURE SCALE S

Temperature is defined asa thermodynamic statevariable.

T-1dQ =0Lord Kelvin 1854:absolute zero point existsfor systems in

thermodynamicequilibrium.T0= -273 .15C

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OVERVIEW OF THERMOMETER TYPES

P rimary ThermometerTemperature measurement is possible

without any prior calibration based on

fundamental law of P hysics.Secondary Thermometer

Temperature measurement is calibrated

via other available thermometer.

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P RIMARY THERMOMETER

Gas Thermometry

Vapor-Pressure Thermometry N oise ThermometersSuperconducting Fixed -P oint ThermometersN uclear -O rientation Thermometers

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S ECONDARY THERMOMETER

Resistance ThermometryCapacitance Thermometry

ThermocouplesR TDs (Resistive Temperature Devices)Thermistors

Integrated CircuitsOptical pyrometersInfrared thermometers

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GA S THERMOMETRY

Ideal gas law

PV = nRT

T (K) =f( P ) / T (K) =f(V)


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THE TWO TY P E S OF GA S THERMOMETER S


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U seful In calibration of secondary thermometer

It is one of the device used to establish the ITS-90

High precision Gas Thermometry is very tediousthus it is used mostly by National laboratories

Good up to the range of 4.2k

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NOI S E THERMOMETER


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Noise spectra taken in the region from 1 K to300 K.


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Karthikeyan Subbu 1 2

Temperatures obtained from the current sensing noise thermometer vs. temperatures from a 3He melting pressure thermometer ( ) and a

platinum NMR thermometer ( )


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NOI S E THERMOMETER

H as a very high resolution of the order of nKThe typical dimensions of the CS N T isapproximately 2X3 mm 2

R and L are chosen to fit the bandwidthrequirement it is usually L & R of the order of 2 nH and 1m



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RE S I S TANCE THERMOMETER S

Basic TheoryThe electrical conductivity of a metal

depends on the movement of electrons throughits crystal lattice. Due to thermal excitation , theelectrical resistance of a conductor variesaccording to its temperature and this forms the

basic principals of resistance thermometry.1. P ositive temperature coefficient2 . N egative temperature coefficient



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TEMP ERATURE DE P ENDENCE OF FEW MATERIAL S


From the graph wecan see that most

of the metal areP TC e.g. P latinumSimilarly thesemiconductors

like germaniumshows a N TC


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S IMP LE S CHEMATIC DIAGRAM FOR THE MEA S UREMENT OF RE S I S TANCE

THERMOMETER


Wheatstone Bridge


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TY P E S OF RE S I S TANCE THERMOMETER S

M etals

Semiconductors(doped)Carbon ResistorsThermoelectric



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CAP ACITANCE THERMOMETRY

Capacitance thermometry works on theprinciple of variation in the dielectricsusceptibility of the material filled inside thecapacitor .

Depending on the material property thedielectric constant varies i.e. either increases ordecreases which can be measured and theoutput is displayed.



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CAP ACITANCE V/ S TEMP ERATURE GRA P H



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CAP ACITANCE V/ S TEMP ERATURE GRA P H


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CAP ACITANCE THERMOMETRY

Capacitance thermometry has a numerousadvantage over the resistance thermometryCapacitance thermometry gives a good resolutionover the resistance thermometryComparatively capacitance thermometer are fieldindependent i.e. its is not affected by the magneticor electric field in the surrounding of themeasurement.



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REFERENCE S

Springerlink.comScience directonline.com

IEEE manuals.comWikipedia



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S UMMARY

Outline of thermometryFour important thermometer of cryogenicimportanceQuestions



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cryogenic thermometry (2)

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