Thermometry is the science of temperature measurement. There are various types of thermometers that use different principles: 1. Liquid-in-glass thermometers use thermal expansion of liquids like mercury. 2. Bimetallic thermometers use the different coefficients of thermal expansion in two metals bonded together. 3. Resistance temperature detectors (RTDs) measure the change in electrical resistance of metals with temperature. Platinum RTDs are commonly used. 4. Thermocouples generate small voltages from the Seebeck effect created by junctions of two different metals and allow temperature measurements over a wide range.

1. THERMOMETRY
Presented by
Dheeraj kakde
Jagadale Saurabh
Sankpal Adesh
Saraf Akshay

2. THERMOMETRY
• Thermometry is the science and
practice of temperature measurement.
• The temperature of a substance is a
measure of the average kinetic energy
of the constituent molecules
• the faster the molecules are moving or
vibrating, the hotter the body will feel.

3. THERMOMETRY (CONTD.)
1. Any measurable change in a thermometric
probe can be used to mark temperature
levels.
i. the dilatation of a liquid in a capillary
tube,
ii. variation of the electrical resistance
of a conductor,
iii. Variation of the refractive index in a
transparent material, and so on
2. Thermometry is also called as science of
the construction and use of thermometers.

4. HISTORY
• Philo of Byzantium (280 - 220 BC) was aware
that air expands and contracts with changes
in temperature
• Demonstration that was developed by Galileo
to become his air thermometer or
thermoscope in around 1600
• This consisted of a glass bulb containing air
with a long tube extending downward into a
container of wine or other coloured liquid

5. HISTORY (CONTD.)
• Engraving a scale on the tube converted
the thermoscope into the first
thermometer.
• The Galilean thermometer was developed
after Galileo’s death, based on principles
that he developed
• Each glass bulb is partially filled with a
coloured liquid and has a metal disc

6. TYPES OF THERMOMETRY
• Contact Thermometry: -
1. when there exists physical contact
between the tested object and the
thermometer.
2. Examples: -
1. Temperature of hot water
2. Temperature of body
• Non Contact Thermometry
1. The non-contact thermometers are
suited for measurements of
temperature of
1. moving or contact sensitive
objects
2. objects inside vacuum,
3. vessels or in hazardous locations
are nowadays widely used in
industry, science, medicine and

7. Non Contact Thermometry
1. Non-contact thermometers employ
different physical phenomena to
determine temperature of the tested
object
1. radiation phenomenon
2. refraction or phase Doppler
phenomenon
3. luminescence phenomenon,

8. WORKING PRINCIPLE OF NON CONTACT
THERMOMETRY

9. CONTACT TYPE
THERMOMETRY

10. LIQUID – IN – GLASS
THERMOMETER
1.Bulb: The reservoir for containing most of the thermometric liquid
2.Stem: The glass tube having a capillary bore along which the liquid
move with changes in temperature.
3. Scale: A narrow-temperature-range scale for reading a reference
temperature .
• The volume of mercury changes slightly with temperature; the small
change in volume drives the narrow mercury column a relatively long way
up the tube.
• The space above the mercury may be filled with nitrogen or it may be at
less than atmospheric pressure, a partial vacuum.
CONSTRUCTION:-

11. WORKING
• Liquid-in-glass thermometer are based on the principle of Thermal expansion of
substances.
• Liquid in glass tube(Capillary) expand when heated and contracts when cooled.
• 𝑉𝑇 = 𝑉𝑇0
1 + 𝛽∆𝑇
𝑉𝑇=Volume of liquid at temperature T, 𝑚3
𝑉𝑇0=Volume of liquid at temperature 𝑇0, 𝑚3
∆𝑇 = 𝑇 − 𝑇0, difference of temperature, K
𝛽= Volumetric thermal expansion coefficient, 1/K
SENSITIVITY
• Sensitivity increases by increasing amount of liquid in the thermometer.
• To much liquid , however, would cause the thermometer to react very slow to
temperature change.

12. Liquid Range
Mercury -35 to 510
Alcohol -80 to 70
Pentene -200 to 30
Toluene -80 to 100
RANGE OF DIFFERENT THERMOMETRIC
LIQUIDS:-

13. CALIBRATION OF LIQUID-IN-GLASS
THERMOMETER:-
For thermometric substances with total length l, the following
equation can be used to determine tempratures in the celcius scale.
𝑙 𝜃 − 𝑙0
𝑙100 − 𝑙0
× 100
Where,
𝑙0 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑜𝑙𝑢𝑚𝑛 𝑎𝑡 0℃
𝑙100 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑜𝑙𝑢𝑚𝑛 𝑎𝑡 100℃
𝑙 𝜃 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑜𝑙𝑢𝑚𝑛 𝑎𝑡 𝜃℃

14. Advantages
1) Simplicity in use & low cost.
2) Portable device.
3) Checking physical damage is easy.
4) Power source not require.
Disadvantages
1) Can not used for automatic recording.
2) Time lag in measurement.
3) Range is limited to about 600 °C .
4) Fragile construction

15. BIMETALLIC THERMOMETER
• In an industry, there is always a need to measure and monitor
temperature of a particular spot, field or locality.
• The industrial names given to such temperature sensors are
Temperature Indicators (TI) or Temperature Gauges (TG).
• All these temperature gauges belong to the class of instruments that are
known as bimetallic sensors.
Two basic principles of operation is to be followed in the case of a
bimetallic sensor:
1. A metal tends to undergo a volumetric dimensional change
(expansion/contraction), according to the change in temperature.
2. Different metals have different co-efficient of temperatures. The rate of
volumetric change depends on this co-efficient of temperature.

16. • Invar (An alloy of Nickel and Iron) is the most commonly
used low expansion materials.
• Nickel-Iron alloys with Chromium and Manganese added are
often used for thermal expansion materials.
CONSTRUCTION

17. • The device consists of a bimetallic strip of two
different metals .
• They are bonded together to form a spiral or a twisted
helix.
• Both these metals are joined together at one end by
either welding or riveting.
• It is bonded so strong that there will not be any
relative motion between the two.
• The image of a bimetallic strip is shown below.
• A change in temperature causes the free end of the
strip to expand or contract due to the different
coefficients of expansion of the two metals.
• This movement is linear to the change in temperature
and the deflection of the free end can be read out by
attaching a pointer to it.
• This reading will indicate the value of temperature.
Bimetallic strips are available in different forms like
helix type, cantilever, spiral, and also flat type.

18. t1= Thickness of low expand material strip, mm
t2= Thickness of high expand material strip, mm
α1= Co-efficient of thermal expansion of low expansion material, /C
α1= Co-efficient of thermal expansion of high expansion material, /C
E1= Modulus of elasticity of low expansion material, N/𝑚𝑚2
E1= Modulus of elasticity of high expansion material, N/𝑚𝑚2
T0= Initial bonding temperature, ℃
T= Operating temperature, ℃
r= Radius of curvature of the bend, mm
L= Length of bimetallic strip, mm
Where, 𝑚 =
𝑡1
𝑡2
𝑛 =
𝐸1
𝐸2
𝑟 =
𝑡1 + 𝑡2 [3 1 + 𝑚 2
+ (1 + 𝑚𝑛) 𝑚2
+
1
𝑚𝑛
6(α1 + α2)(𝑇 − 𝑇0)(1 + 𝑚)2
RADIUS OF CURVATURE OF
BIMETALLIC STRIP:-

19. Variation of Radius with respect to temperature
for bimetallic strip:-

20. Advantages
1. Power source not required
2. Robust, easy to use and cheap.
3. Can be used to 500 °C.
Disadvantages
1. Not very accurate.
2. Limited to applications where manual reading is acceptable.
3. Not suitable for very low temperatures because the expansion of
metals tend to be too similar, so the device becomes a rather
insensitive thermometer

21. RESISTANCE
TEMPERATURE DETECTOR
(RTD)
 PRINCIPLE : TEMPATURE = RESISTANCE
 Positive temperature coefficient
 classified according to the different sensing elements
used –Platinum, Nickel, Copper
 RTDs are more accurate but also larger and more
expensive than thermocouples.

22.  Electrical Resistivity For Solid = ρ =
ρ0(1+α(T-T0)
Metal ρ0 (Ω·mm2/m ) α (1/K)
Commercial
Copper
0.017 0.0039
Nickel 0.068 0.007
Wolfram 0.054 0.0045
Platinum 0.11 0.003850
 Platinum is used in most instances because of its wide
temperature range, accuracy, linearity, and stability
 No special extension cables or cold-junction compensation
is required,
 Wheatstone bridge are used to eliminate the connection
lead resistance effects from measurements
Introduction

23. Fig. Immersion probe and internal details of a RTD
probe.
RTD Probe Details

24. Wheatstone bridge Circuit
 Wheatstone bridge are used to eliminate the connection
lead resistance effects from measurements.
𝐺
𝑉
=
(𝑅2 × 𝑅𝑇) − (𝑅1 × 𝑅3)
(𝑅1 + 𝑅𝑇𝐷) × (𝑅2 + 𝑅3)

25. Fig. RTD For 2-Wires,3-Wires,4-Wire Systems
RTD For 2-Wires,3-Wires,4-Wire
Systems

26. Temperature Detectors (RTD)
Advantages
1) The sensor can be easily installed and replaced.
2) Good measurement accuracy (± 0.25% of scale range)
3) Fast response and good reproducibility.
4) Resistance to corrosion, chemicals, and oxidation.
5) Wide temperature range. (-180 °C to 760 °C )
6) Remote temperature sensing is possible.
7) No reference junction required.
8) Stable and accurate performance over a long time.
9) No necessity for any temperature compensation.
Disadvantages
1) More expansive than other instruments.
2) Large bulb size compared to thermocouple.
3) Required a separate bridge circuit system.
4) External power source required.
5) The self heating caused by current flow affects the accuracy of the
instrument.

27. Thermocouples
Fig.Basic Thermocouple
Circuit
 Thermocouples are metal couples which work on the Seebeck effect.
 In this effect, any conductor is subjected to a thermal gradient, it
will generate a voltage.
 There are about 4 to 5 types of thermocouples which are
categorized based on sensitivity and range.
 J Type, K Type, E Type, T Type and N Type
 For small DT’s, the relationship with temperature is linear
 For larger DT’s, non-linearities may occur.
V TD  D

28. Working
Fig. Schematic Dia Of Thermoelectric Pyrometer
 Thermo means heat and couple means to make the junction.
 Thermocouple works on thermoelectric effect.
 It consist of
(1) Sensing element with thermal wall (Sheathing), measuring Junction
(2) Lead wire
(3) Reference junction
(4) Current measuring and indicating device, millivoltmeter or potentiometer
type instrument.

29.  The two dissimilar wires welded or soldered to from two junction.
 The wires are insulated from each other and covered by protective
sheathing.
 Thermal EMF developed upon the difference between measuring junction
and reference junction temperature.
 The magnitude of the electric voltage developed by thermocouple due to
temperature different between junction.
 Measure the small voltage change using millivoltmeter or thepotentiometer
Working
Fig. Thermocouples

30. Thermocouple Temp Vs Voltage
Graph
Thermocouple Temp Vs
Seeback coeff Graph

31. Error In Thermocouple

32. Advantages
1) Thermocouple have a better response.
2) They have a higher range of temperature measurements.
3) They sensing elements of thermocouple is easily installed.
4) Cheaper than RTD.
5) Very convenient for measuring the temperature at one particular point in
a piece of apparatus.
Disadvantages
1) Lower accuracy and as such they cannot be used for precision work.
2) Limited life of thermocouple.
3) The circuitry for thermocouple is very complex.
4) Expensive wire.
5) Need known reference.

33. Comparison Of Thermocouple & RTD

34. Thermistors:
• The word ‘Thermistor’ is the combination of
Thermal and Resistor.
• A thermistor is a type of resistor whose
resistance is dependent on temperature.
• Types of Thermistors:
Negative temperature Coefficient(NTC) type.
Positive temperature Coefficient(PTC) type.
• A typical Operating Temperature range of
Thermistors is (-55 to 150) degree celcius.
• Thermistors differ from resistance temperature
detectors (RTDs) in that the material used in a
thermistor is generally a ceramic or polymer,
while RTDs use pure metal.

35. Basic Operation:
• Assuming, as a first-Order approximation,
that the relationship between Resistance and
temperature is linear, then
ΔR=KΔT,
where, ΔR = Change in Resistance,
ΔT= Change in Temperature,
K= First Order temperature
Coefficient of Resistance.
• Thermistors can be classified into two types,
depending on the sign of K. (i.e. Positive
temperature coefficient(PTC) and Negative
temperature coefficient(NTC) type.

36. Conduction Model:
1] Negative Temperature coefficient(NTC)
• NTC thermistors are made from a pressed disc, rod,
plate, bed or caste chip of semiconducting material
such as Sintered metal oxides.
• They work because raising the temperature of a
semiconductor increases the number of active charge
carriers, it promotes them into the conduction band.
• The more charge carriers that are available, the
more current a material can conduct.
• The more the current conducted, the less will be its
Resistance.
• This is described in the formula,
I= ρAve

37. 2] Positive temperature coefficient(PTC):
• Most PTC thermistors are made from doped polycrystalline
ceramic (containing barium titanate (BaTiO3) and other
compounds.
• These material have the property that their resistance rises
suddenly at a certain critical temperature.
• Below the Curie point temperature, the high dielectric
constant prevents the formation of potential barriers
between the crystal grains, leading to a low resistance.
• At Curie point temperature, the dielectric constant drops
sufficiently to allow the formation of potential barriers at
the grain boundaries,and the resistance increases sharply
with temperature.

38. Applications:
1] PTC:
-As Current limiting devices for circuit problem.
-In temperature compensated synthesizer voltage controlled
Oscillators.
-In Lithium Battery protection circuits.
-In an electrically actuated wax motor to provide the heat
necessary to
expand the wax.
2] NTC:
- As a resistance thermometer for low temperature
measurements of the
order of 10K.
-To monitor the temperature of an Incubator.
-Modern digital thermostats.
-3 D printers.

39. Calibration of Thermistors:
• Linear approximation is valid only for limited tem-
perature range but not for wide temperature range.
• According to Steinhart-Hart equation,
(1/T)= a + b x lnR + c x (lnR)^3
…..{3rd Order approximation}
• Resistance as the function of temperature is also
expressed as,

40. Advantages:
• It has fast response over narrow temperature range.
• It is small in Size.
• Contact and lead resistance problem not occurred due to large resistance.
• It has good sensitivity in NTC region.
• Its cost is low.
Disadvantages:
• The Thermistor needs shielding Power lines.
• The excitation current should be low to avoid self heating.
• Not suitable for large temperature range.
• Resistance – Temperature characteristics are non linear.