Introduction to Temperature Measurement Nihal Gunasekara Sri Lanka Bangladesh BEST programme

Introduction to Temperature Measurement

Nihal GunasekaraSri Lanka

Bangladesh BEST programme

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Temperature and Scale

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

Bangladesh BEST Programme

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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


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


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


Equilibrium State

Bangladesh BEST programme

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Metal Fixed-Point


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Number Substances StateDefining temperature

K oC

1

2

3

4

5

6

7

8

9

He

e-H2

e-H2 (He)

e-H2 (He)

Ne

O2

Ar

Hg

H20

V

T

V(G)

V(G)

T

T

T

T

T

3 to 5

13.8033

~17

~20.3

24.5561

54.3584

83.8058

234.3156

273.16

-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

9

10

11

12

13

14

15

16

17

H20

Ga

In

Sn

Zn

Al

Ag

Au

Cu

T

M

F

F

F

F

F

F

F

273.16

302.9146

429.7485

505.078

692.677

933.473

1234.93

1337.33

1357.77

0.01

29.7646

156.5985

231.928

419.527

660.323

961.78

1064.18

1084.62

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 -259.3467

Hydrogen (or He) Vapour pressure 20.3 -252.85

Neon Triple point 24.5561 -248.5939

Oxygen Triple point 54.3584 -218.7916

Argon Triple point 83.8058 -189.3442

Mercury (Hg) Triple point 234.3156 -38.8344

Water (H2O) Triple point 273.16 0.01

Gallium (Ga) Melting point 302.9146 29.7646

Indium (In) Freezing point 429.7485 156.5985

Tin (Sn) Freezing point 505.078 231.928

Zinc (Zn) Freezing point 692.677 419.527

Aluminum (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


Thermoelectric theory(Seebeck effect)

• In 1821, T.J.Seebeck found

Hot Cold emf

A

B

Cold

A and B are two different metallic wires.


Practical Usage

MeasuringInstrument

Measuring pointExtension wires

Reference junctions

Thermocouple wires


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


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


R Platinum-13% rhodium alloy/paltinum


S Platinum-10% rhodium alloy/platinum


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

alloy



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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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• 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



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

Measuring Range : -20 °C to 600 °C


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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


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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

Bangladesh BEST Programe

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Thank You

Documents

Introduction to Temperature Measurement Nihal Gunasekara Sri Lanka Bangladesh BEST programme