introduction to temperature measurement

Introduction to Temperature Measurement

Nihal GunasekaraSri Lanka

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Temperature and Scale

• What is temperature ?• The first thermometer • Types of scale• Classification of thermometer• International Temperature Scale

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What is temperature ?

• Ruler for the cool and hot ?– Motivation of the thermometer development

• The zeroth law of thermodynamics

• Temperature means the level of thermal energy.• Driving force for the heat flow

A B C

Thermal equilibrium

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The first thermometer

• In 1594, G. Galileo– A type of gas thermometer– Volume change with temperature

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The First Glass Thermometer– In 1654, Ferdinand II, Grand Duke of Tuscany

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• The first mercury thermometer– In 1706, Netherlands, Fahrenheit

• The first platinum resistance thermometer– In late 19th century, Callendar

• The first commercial thermocouple– In 1885, Le Chatelier, Type S

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History of Thermometry

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Types of Scale

Fahrenheit (oF)– In 1706, Netherlands, Fahrenheit

• In Europe, coldest day : 0 oF (= - 17.8 oC)• Hottest day : 100 oF (= 37.8 oC)• 0 oC = 32 oF• 100 oC = 212 oF

oF = 9/5 oC + 32

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• degree Celsius (oC)– In 1742, Sweden - A. Celsius

• Ice point : 0 oC• Water boiling point : 100 oC • Divided into 100 parts

– Currently used together with international unit

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Defining Temperature Scale

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Absolute temperature - K ( thermodynamic temperature) In 1848, Lord KelvinThe second law of thermodynamics and Carnot heat engine

K = oC + 273.15 International unit of temperature scale

16.273 waterofpoint TripleK 1

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• History of International Temperature Scale

1927, The International Temperature Scale of 1927 (ITS-27)

1948, The ITS-481960, Amended edition of the ITS-481968, The International Practical Temperature Scale of

1968 (IPTS-68)1976, Amended edition of the IPTS-681990, The ITS-90

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International Temperature Scale of 1990Bangladesh BEST programme

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• Triple Point of Water– Distilled water– De-ionized water– Air-free state– Water + Vapor +

Ice– Reference of

scale

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Equilibrium State Bangladesh BEST programme

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Metal Fixed-Point

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Number Substances StateDefining temperature

K oC

123456789

He

e-H2

e-H2 (He)

e-H2 (He)

Ne

O2

ArHg

H20

VT

V(G)V(G)

TTTTT

3 to 513.8033

~17~20.3

24.556154.358483.8058234.3156273.16

-259.3467

-248.5939-218.7916-189.3442-38.8344

0.01

Fixed-points Below 273.16 K Bangladesh BEST Programme

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Number Substances StateDefining temperature

K oC

91011121314151617

H20

GaInSnZnAlAgAuCu

TMFFFFFFF

273.16302.9146429.7485505.078692.677933.4731234.931337.331357.77

0.0129.7646156.5985231.928419.527660.323961.781064.181084.62

Fixed-points Above 273.16 K

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Defining Fixed Points of ITS -90 Bangladesh BEST Programme

Material Equilibrium State Temperature (K) Temperature (°C )

Hydrogen Triple point 13.8033 -259.3467Hydrogen (or He) Vapour pressure 20.3 -252.85

Neon Triple point 24.5561 -248.5939Oxygen Triple point 54.3584 -218.7916Argon Triple point 83.8058 -189.3442

Mercury (Hg) Triple point 234.3156 -38.8344Water (H2O) Triple point 273.16 0.01Gallium (Ga) Melting point 302.9146 29.7646Indium (In) Freezing point 429.7485 156.5985

Tin (Sn) Freezing point 505.078 231.928

Zinc (Zn) Freezing point 692.677 419.527Aluminum (Al) Freezing point 933.473 660.323

Silver (Ag) Freezing point 1234.93 961.78

Gold (Au) Freezing point 1337.33 1064.18

Copper (Cu) Freezing point 1357.77 1084.62

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Different Types of Thermometers

Thermocouple thermometers Resistance thermometers Liquid-in-glass thermometers Bimetallic thermometers Radiation thermometers Optical pyrometers

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Thermoelectric theory(Seebeck effect)

• In 1821, T.J.Seebeck found

Hot Cold emf

A

B

Cold

A and B are two different metallic wires.

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Practical Usage

MeasuringInstrument

Measuring pointExtension wires

Reference junctions

Thermocouple wires

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Reference (cold ) Junction

• Accurate Measurements Ice Bath

• Modern TC Thermometers Compensation incorporated

• C J at a Constant Temp. Isothermal Block

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Types and Materials Type Materials Allowable environment Max.

operating temp. °C

T Copper/Copper-nickel alloy Oxidising, reducing, inert or vacuum 370

J Iron/copper-nickel alloy Oxidising, reducing, inert or vacuum 760

E Nickel-chromium ally/copper-nickel alloy

Oxidising or inert 870

K Nickel-chromium alloy/nickel aluminium alloy

Oxidising or inert 1260

N Nickel-chromium-silicon alloy /nickel silicon-magnesium alloy

Oxidising or inert 1260

R Platinum-13% rhodium alloy/paltinum

Oxidising or inert 1480

S Platinum-10% rhodium alloy/platinum

Oxidising or inert 1480

B Platinum-30% rhodium alloy/platinum- 6%rhodium

alloy

Oxidising or inert 1700

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Resistance Thermometers

Platinum Resistance Thermometers (PRT) Standard Platinum Resistance Thermometers (SPRT) High Temperature Platinum Resistance Thermometers

(HTPRT)

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Resistance Thermometers

• PRT Pt-100 100 Ω at 0 °C Working Standard

• SPRT 25 Ω at 0 °C Reference Standard

• HTPRT 2.5 Ω at 0 °C Reference Standard

• Available in the Range - 200 °C to 1000 °C

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Principle of Operation

• Change in Temperature of a Resistive Element

Resistance Value Changed

Platinum Element

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Terminal Configuration Red White Red Red White

Pt -100/2 Pt – 100/3 Red Red White White

Pt- 100/4

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Resistance Thermometers

27n

Construction Thin Film PRT

Long stem SPRT Reference SPRT

PRT-100

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Liquid in Glass Thermometers

• Principle of Operation : Expansion of Liquid in a Glass Capillary Tube to Sense the Temperature

• Measuring Range : -20 °C to 600 °C

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Liquid in Glass Thermometers

Condition of Immersion Total Immersion Thermometers Partial Immersion Thermometers Complete Immersion Thermometers

Measuring Range : -20 °C to 600 °C

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Liquid in Glass Thermometers

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Bimetallic Thermometers

Principle of Operation : Difference in the Thermal Expansion of Two Metals

Measuring Range : -100 °C to 540 °C

Accuracy : about 1% of reading

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Bimetallic Thermometers Bangladesh BEST Programme

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Radiation Thermometers

• Principle of Operation : As the temperature of the object increases more energy is emitted at progressively shorter wavelengths

• Measuring Range : 600 °C to 3500 °C

• Detectors : Mostly Silicon or Germanium

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Relationship Between Wavelength of the Emitted Radiation and Spectral Radiance

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Optical Pyrometers

Disappearing filament type

Constant radiation disappearing filament type

Automatic optical type

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Disappearing Filament Type Pyrometer

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Constant Radiation Disappearing Filament Type Pyrometer

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