The document discusses the principles and methods of temperature measurement, including definitions of temperature, types of thermometers (liquid-in-glass, bimetallic, pressure, resistance, thermocouples, and pyrometers), and their respective operating principles and temperature ranges. It explains the significance of fixed points in temperature scales, such as the triple point of water, and details various temperature measurement techniques based on physical properties. Additionally, it addresses the calibration of thermometers and the importance of understanding thermal expansion, resistance, and radiation in the context of temperature measurement.

1. Temperature
Measurement
PREPARED BY : RATNADEEPSINH JADEJA

2. Introduction
 The temperature is a thermal state of a body which distinguishes a hot body from
a cold body. The temperature of a is proportional to the stored molecular energy
i.e. the average molecular kinetic energy of the molecules in a system.
 The temperature may also be defined as:
 The measure of the mean K.E. of the molecules of a substance.
 The degree of hotness and coldness of a body or an environment measured on a
definite scale.
 The driving force or potential causing flow of energy as heat.

3. Introduction
 Instruments for measurement of ordinary temperatures are known as
thermometers and those for measuring high temperatures are known as
pyrometers,
Thermometer
Pyrometer

4. Introduction
 It has been found that a gas will not
occupy any volume at a particular
temperature. This temperature is
known as absolute zero temperature.
The temperatures measured with
absolute zero as basis are called
absolute temperatures. The point of
absolute zero temperature is found
to occur at 273.15 °C below the
freezing temperature of water.

5. Thermometer Thermometric property
Constant volume gas Pressure (p)
Constant pressure gas Volume (V)
Alcohole or mercury in glass Length (L)
Electric resistance Resistance (R)
Thermocouple Electromotive force (E)
Radiation (Pyrometer) Intensity of radiation (I or J)

6. Temperature Scale
 For the calibration of thermometric instruments the seventh general conference
on weight and measures held in 1927 formulated a convenient scale known as
the International Practical Temperature Scale. It was revised at thirteenth
general conference in 1968. It consists of reproducible reference temperatures or
primary fixed point s defined by a number of pure substances with assigned
values of temperatures.
 The triple point represents an equilibrium state between solid, liquid and vapour
phases of a substance.
 Normal boiling point is the temperature at which the substance boils at
standard atmospheric pressure of 760 mm Hg.
 Normal freezing point is the solidification or the melting point temperature of
the substance at standard atmospheric pressure.

7. Temperature Scale
Equilibrium state T, K T, °C
Triple point of Hydrogen 13.81 -259.34
Normal Boiling point of Hydrogen 20.28 -252.87
Triple point of Oxygen 54.361 -218.789
Normal boiling point of Oxygen 90.188 182.962
Triple point of water 273.16 0.01
Normal boiling point of water 373.15 100.00
Normal freezing point of antimony (antimony point) 630.74 357.59
Normal freezing point of zinc (zinc point) 692.73 419.58
Normal freezing point of silver (silver point) 1235.08 961.93
Normal Freezing point of gold (gold point) 1337.58 1064.43

8. Temperature Scale
 The fixed points for these temperature scales before 1954
 The use of two fixed point found unsatisfactory and later abandoned because of
the following reasons:
1. It is difficult to achieve equilibrium between pure ice and air saturated water.
2. There is extreme sensitiveness of the steam point to the change in pressure.
Temperature Celsius scale Fahrenheit scale
Steam point 100 212
Ice point 0 32
Interval 100 180

9. Temperature Scale
 After 1954
It was suggested by Kelvin that a single fixed point only was necessary to establish a
temperature. He pointed out that triple point of water could be used as a single
point.
𝐾 = °𝐶 + 273.15

10. Temperature Measuring Instruments
 The temperature measuring instruments are based on changes in a broad range
of physical properties, among which are the following:
1. Change in physical dimensions
2. Change in gas pressure or vapour pressure
3. Change in electrical properties
4. Change in emitted thermal radiation
5. Change in chemical phase

11. Temperature Measuring Instruments
 The thermometers may also be classified as follows:
1. Expansion thermometers
 Liquid in glass tube thermometers
 Bimetallic thermometers.
2. Pressure thermometers
 Vapour pressure thermometers
 Liquid filled thermometers
 Gas filled thermometers
3. Resistance thermometers
4. Thermocouple thermometers
5. Radiation pyrometers
6. Optical pyrometers

12. Liquid in Glass Thermometer
 The mercury or other liquid fills the glass bulb and
extends into the bore of the glass stem. Mercury is the
most suitable liquid and is used from -38.9 °C to about
600 °C.
Liquid Boiling point °C Freezing point °C
Pentane 36 -130
Ethyl alcohol 78 -100
Toluene 110 -92

13. Calibration
 All the portion of a glass thermometer
are temperature sensitive, yet greatest
sensitivity to temperature is at the
bulb, where the largest volume of
liquid is contained.

15. Bimetallic Thermometers
In a bimetallic thermometer
differential expansion of bimetallic
strips is used to indicate the
temperature.
 The bimetallic thermometers are made with metals which have widely different
thermal expansion coefficients.
 In order to protect the bimetallic thermometers against wear and corrosion, they
are usually mounted in wells.
 Invar (an alloy of nickel and iron), Nickel-iron alloys with chromium and
manganese added are often used for thermal expansion material

16. Helical type
Bimetallic
Thermometers

17. Spiral type
Bimetallic
Thermometers

18. Pressure Thermometers
 In pressure thermometers liquids, gases and vapours can all be used.
 The fluid is confined in a closed system. In this case pressure is a function of the
temperature, so that when the fluid is heated, the pressure will rise. And the
temperature can be indicated by bourdon type pressure gauge.
 The following pressure thermometers can be used.
1. Vapour pressure thermometer.
2. Liquid filled thermometer
3. Gas filled thermometer.
 These devices are commonly known as Filled systems.

19. Pressure Thermometers

20. Static Errors in Filled Systems
 The sources of static errors in filled systems are:
1. The ambient temperature effect.
2. The head effect.
3. The barometric effect.
4. The immersion effect.

21. Electrical Resistance Thermometer or RTD
 Electrical methods of temperature measurement
are very convenient due to the following reasons:
1. They furnish signal that is easily detected,
amplified or used for control purpose.
2. They are usually quite accurate when properly
calibrated and compensated..
 Range of temperature from -200 to 650 °C.
 If the electrical resistance of a wire of known and
calibrated material is measured, the temperature of
the wire can be determined. The resistance element
should be of a suitable metal having high temperature
coefficient, reproducibility, stability and ability to resist
corrosion and oxidation.

22. Thermistors
 A thermistor (Thermal Resistor) is a thermally sensitive variable resistor made of a
ceramic like semi conducting material.
 Thermistors, unlike metals, respond negatively to temperature; as the
temperature rises, the thermal resistance decreases.
 Thermistors are often composed of oxides of manganese, nickel and cobalt
formulations having resistivities of 100 to 450000 Ω in cryogenic applications,
doped germanium and carbon-impregnated glass are used.
 The electrical characteristics of thermistors are controlled by varying the type of
oxide used and physical size and configuration of the thermistor.
 The platinum resistance thermometer: 300 °C to 400 °C
 Copper resistance thermometer: 0 °C to 180 °C.

23. Thermocouple
Thermometer

24. Thermocouple Thermometer
 For higher range of temperatures i.e. above 650 °C, filled thermometers are
unsuitable. For higher range of temperatures, thermocouples and pyrometers are
used.
 Seebeck effect: When the two junctions of a pair of dissimilar metals are
maintained at different temperatures, e.m.f. (electromotive force) is generated.
The phenomenon of generation of e.m.f is called Seebeck effect.
 Peltier effect: If direct current is passed through a pair of dissimilar metals, there
us a heating at one junction, cooling at the other depending upon the material
combinations.

25. Thermocouple Thermometer
 Materia and Range of thermocouple.
 Platinum vs platinum-rhodium : 400 to 1450 °C.
 Chromel vs alumel : -200 to 1200 °C.
 Iron vs constantan : -200 to 750 °C.
 Copper vs constantan : -200 to 350 °C.

26. Radiation Pyromoters
 Radiation heat transfer is
defined as “the transfer of
energy across a system
boundary by means of an
electromagnetic mechanism
which is caused solely by a
temperature difference.”
 Where as the heat transfer by
conduction and convection
takes place only in the
presence of medium, radiation
heat transfer does not require a
medium.

27. Radiation
Pyromoters
 The principle, that the radiant
energy emitted from a body
increases with temperature, is
used in measuring temperatures
particularly in the higher ranges.
 A device which measures the
total intensity of radiation
emitted from a body is called
total radiation pyrometer.

28. Optical Pyromoters
 An optical pyrometer works on the principle that matters glow above 480 °C and the
colour of visible radiation is proportional to the temperature of the glowing matter.

29. Optical Pyromoters