In this presentation we have discussed about temperature measuring instruments used in industry. Like Mechanical , electrical and non contact types instruments for measuring temperature

1. Name- Anjani Kishor Rishabh
Enrollment Number-21546001
M.Tech Pulp and Paper Technology (2021-
23), IIT ROORKEE

2. BASICS
• Temperature is as fundamental a physical concept as the three basic quantities of mechanics:
mass, length, and time. Temperature is an expression that denotes a physical condition of
matter.
• Temperature is a measure of the thermal energy in a body, which is the relative hotness or
coldness of a medium and is normally measured in degrees using one of the following scales;
• Fahrenheit (F)
• Celsius or Centigrade (C)
• Rankine (R)
• Kelvin (K)
• Absolute zero is the temperature at which all molecular motion ceases or the energy of the
molecule is zero.

3. COMPARISON OF TEMPERATURE SCALE

4. HEAT
• Heat is a form of energy; as
energy is supplied to a system the
vibration amplitude of its
molecules and its temperature
increases. The temperature
increase is directly proportional to
the heat energy in the system

5. THERMAL
EXPANSION
LINEAR
THERMAL
EXPANSION
VOLUME
THERMAL
EXPANSION

6. LINEAR THERMAL EXPANSION
• Linear thermal expansion is the change in dimensions of a material due to temperature
changes. The change in dimensions of a material is due to its coefficient of thermal
expansion that is expressed as the change in linear dimension per degree temperature
change.
Where L2 = final length
L1 = initial length
α = coefficient of linear thermal expansion
T2 = final temperature
T1 = initial temperature
L2 = L1 [1 + α (T2 − T1)]

7. VOLUME THERMAL EXPANSION
• Volume thermal expansion is the change in the volume per degree temperature
change due to the linear coefficient of expansion
Where V2 = final volume
V1 = initial volume
β = coefficient of volumetric thermal expansion
T2 = final temperature
T1 = initial temperature
V2 = V1 [1 + β (T2 − T1)]

8. TEMPERATURE MEASURING DEVICES
Expansion
Thermometer
Filled System
Thermometer
Electrical
Measurement
thermometer
Pyrometer

9. EXPANSION THERMOMETER ->MERCURY
THERMOMETERS
• The most common direct
visual reading thermometer
• The operating range of the
mercury thermometer is
from −30 to 800°F (−35 to
450°C) (freezing point of
mercury −38°F [−38°C]).

10. CONSTRUCTION AND WORKING
• The device consisted of a small bore graduated glass tube with a small bulb
containing a reservoir of mercury. The coefficient of expansion of mercury is several
times greater than the coefficient of expansion of glass, so that as the temperature
increases the mercury rises up the tube giving a relatively low cost and accurate
method of measuring temperature.

11. Advantages Disadvantages
• Simple in construction,
• Relatively inexpensive,
• Easy to use and portable,
• The most widely used method
of temperature measurement
having industrial, chemical,
clinical and meteorological
applications.
• Fragile and hence easily broken,
Can only be used where the liquid
column is visible,
• Cannot be used for surface
temperature measurements,
• Cannot be read from a distance
and are
• Unsuitable for high temperature
measurements.

12. LIQUIDS IN GLASS DEVICES
• Liquids in glass devices operate
on the same principle as the
mercury thermometer.
• The liquids used have similar
properties to mercury, i.e., high
linear coefficient of expansion,
clearly visible, non-wetting, but
are nontoxic.

13. • The liquid in glass thermometers
is used to replace the mercury
thermometer and to extend its
operating range.
• These thermometers are
accurate and with different
liquids can have an operating
range of from −300 to 600°F
(−170 to 330°C).

14. BIMETALLIC STRIP
• It is relatively inaccurate, slow to respond, not normally used in analog applications to give remote indication, and has
hystersis.
• The bimetallic strip is extensively used in ON/OFF applications not requiring high accuracy, as it is rugged and cost effective.
• Their operating range is from −180 to 430°C and can be used in applications from oven thermometers to home and industrial
control thermostats.

15. PRINCIPLE
• Bimetal thermometers work on the
principle that different metals
expand at different rates as they
are heated. By using two strips of
different metals in a thermometer,
the movement of the strips
correlates to temperature and can
be indicated along a scale.

16. BIMETALLIC THERMOMETERS WORKING
A bimetallic thermometer is a temperature
measurement device. It converts the media’s
temperature into mechanical displacement
using a bimetallic strip. The bimetallic strip
consists of two different metals having different
coefficients of thermal expansion.
Bimetallic thermometers are used in
residential devices like air conditioners, ovens,
and industrial devices like heaters, hot wires,
refineries, etc.

17. CONSTRUCTION AND DESIGN
• A bimetallic thermometer works by using two basic properties of metal:
• The thermal expansion property of the metal
• The coefficient of thermal expansion of different metals is different for the same
temperature.
• The main component of the bimetallic thermometer is the bimetallic strip. The bimetallic
strip consists of two thin strips of different metals, each having different coefficients of
thermal expansion. Thermal expansion is the property of a metal to change its shape or
volume with a change in temperature. The metal strips are connected along their length
by fusing them together or riveting. The strips are fixed at one end and free to move on
the other end.

20. WORKING
• The two metals typically used are steel and copper, but steel and brass can also be
used. Since their thermal expansion is different, the length of these metals changes
at different rates for the same temperature. Due to this property, when the
temperature changes, the metal strip at one side expands and the other does not,
which creates a bending effect.
• When the temperature rises, the strip will turn in the direction of metal with the
lower temperature coefficient. When the temperature decreases, the strip bends in
the direction of metal having a higher temperature coefficient. The deflection of the
strip indicates the temperature variation. This bending motion is connected to the
dial on the thermometer, outputting the media’s temperature.

21. Advantages Disadvantages
• Simple and robust design
• Less expensive than other
thermometers
• They are fully mechanical and
do not require any power
source to operate.
• Easy installation and
maintenance
• Nearly linear response to
temperature change
• Suitable for wide temperature
ranges
• They are not advised to use for
very high temperatures.
• They may require frequent
calibration.
• May not give an accurate reading
for low temperature.
• Calibration is disturbed if roughly
handled

22. PRESSURE-SPRING THERMOMETERS
• These thermometers are used where remote indication
is required, as opposed to glass and bimetallic devices
which give readings at the point of detection.
• The pressure-spring device has a metal bulb made
with a low coefficient of expansion material with a long
metal tube, both contain material with a high
coefficient of expansion; the bulb is at the monitoring
point.
• The metal tube is terminated with a spiral Bourdon
tube pressure gage (scale in degrees) as shown in Fig.

23. • The pressure system can be used to drive a chart
recorder, actuator, or a potentiometer wiper to obtain an
electrical signal.
• As the temperature in the bulb increases, the pressure
in the system rises, the pressure rise being proportional
to the temperature change.
• The change in pressure is sensed by the Bourdon tube
and converted to a temperature scale. These devices can
be accurate to 0.5 percent and can be used for remote
indication up to 100 m but must be calibrated, as the
stem and Bourdon tube are temperature sensitive.

25. Electrical
Methods
Thermistor
Resistance
Thermometer
Thermocouple

26. THERMISTORS- BASICS
• Thermistors are a class of metal oxide (semiconductor material) which typically have
a high negative temperature coefficient of resistance, but can also be positive.
• Thermistors have high sensitivity which can be up to 10 percent change per degree
Celsius, making them the most sensitive temperature elements available, but with
very nonlinear characteristics.
• The typical response times is 0.5 to 5 s with an operating range from −50 to typically
300°C. Devices are available with the temperature range extended to 500°C.

27. • Definition: The thermistor is a kind of resistor whose resistivity depends on
surrounding temperature. It is a temperature sensitive device. The word thermistor is
derived from the word, thermally sensitive resistor. The thermistor is made of the
semiconductor material that means their resistance lies between the conductor and
the insulator.
• The variation in the thermistor resistance shows that either conduction or power
dissipation occurs in the thermistor. The circuit diagram of thermistor uses the
rectangular block which has a diagonal line on it.
Symbol of thermistor

28. TYPES OF THERMISTOR
• The thermistor is classified into types. They are the negative
temperature coefficient and the positive temperature coefficient
thermistor.
• 1. Negative Temperature Coefficient Thermistor – In this type of
thermistor the temperature increases with the decrease of the
resistance. The resistance of the negative temperature coefficient
thermistor is very large due to which it detects the small variation
in temperature.
• 2. Positive Temperature Coefficient Thermistor – The resistance of
the thermistor increases with the increases in temperature.

29. CONSTRUCTION
• 1. The thermistor is made with the sintered mixture
of metallic oxides like manganese, cobalt, nickel,
cobalt, copper, iron, uranium, etc.
• 2. It is available in the form of the bead, rod and
disc.
• 3. The bead form of the thermistor is smallest in
shape, and it is enclosed inside the solid glass rod to
form probes.
• 4. The disc shape is made by pressing material under
high pressure with diameter range from 2.5 mm to
25mm.
• 5. Following figures show
various types of construction of thermistors:

30. • Thermistors are low cost and manufactured in a wide range of shapes, sizes, and
values. When in use care has to be taken to minimize the effects of internal heating.
Thermistor materials have a temperature coefficient of resistance (α) given by
• where ∆R is the change in resistance due to a temperature change
• ∆T and RS the material resistance at the reference temperature.
The nonlinear characteristics are as shown in Fig. 8.5 and make the device difficult to use as
an accurate measuring device without compensation, but its sensitivity and low cost makes it
useful in many applications.
The device is normally used in a bridge circuit and padded with a resistor to reduce its
nonlinearity.

31. WORKING
• The thermistor act as a temperature sensor and it is placed on a body whose
temperature is to be measured. It is also connected to electrical circuit.
• When the temperature of the body changes, the resistance of the body also changes,
which is directly indicated by the circuit as the temperature since the resistance is
calibrated against the temperature.

32. RESISTANCE TEMPERATURE
CHARACTERISTIC OF THERMISTOR
• The resistance temperature
coefficient of the thermistor is
shown in the figure below.
• The graph below shows that the
thermistor has a negative
temperature coefficient, i.e., the
temperature is inversely
proportional to the resistance.

33. Advantages Disadvantages
• The thermistor 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.
• Cost is low.
• The thermistor need of
shielding power lines.
• The excitation current
should be low to avoid
self heating.
• It is not suitable for
large temperature
range.
• The resistance
temperature
characteristics are non
linear.

34. RESISTANCE TEMPERATURE DEVICES
• Resistance temperature devices (RTD) are either a metal film deposited on a former
or are wire-wound resistors. The devices are then sealed in a glassceramic composite
material. The electrical resistance of pure metals is positive, increasing linearly with
temperature. Table 8.5 gives the temperature coefficient of resistance of some
common metals used in resistance thermometers. These devices are accurate and
can be used to measure temperatures from −300 to 1400°F (−170 to 780°C). In a
resistance thermometer the variation of resistance with temperature is given by
RT2 = RT1 (1 + Coeff. [T2 − T1]) (8.14) where RT2 is the resistance at temperature
T2 and RT1 is the resistance at temperature T1

35. • The resistance thermometer or resistance temperature detector (RTD) uses the
resistance of electrical conductor for measuring the temperature.
• The resistance of the conductor varies with the time. This property of the conductor is
used for measuring the temperature.
• The main function of the RTD is to give a positive change in resistance with
temperature.
• The metal has a high-temperature coefficient that means their temperature increases
with the increase in temperature. The carbon and germanium have low-temperature
coefficient which shows that their resistance is inversely proportional to temperature.

36. MATERIAL USED IN RESISTIVE
THERMOMETER
• The resistance thermometer uses a sensitive element made of extremely pure metals like platinum,
copper or nickel.
• The resistance of the metal is directly proportional to the temperature. Mostly, platinum is used in
resistance thermometer. The platinum has high stability, and it can withstand high temperature.
• Gold and silver are not used for RTD because they have low resistivity. Tungsten has high resistivity, but
it is extremely brittles.
• The copper is used for making the RTD element. The copper has low resistivity and also it is less
expensive.
• The only disadvantage of the copper is that it has low linearity. The maximum temperature of the copper
is about 120ºC.
• The RTD material is made of platinum, nickel or alloys of nickel. The nickel wires are used for a limited
temperature range, but they are quite nonlinear.

37. • The following are the requirements of the conductor used in the RTDs.
• The resistivity of the material is high so that the minimum volume of conductor is used
for construction.
• The change in resistance of the material concerning temperature should be as high as
possible.
• The resistance of the material depends on the temperature.

38. THE RESISTANCE
VERSUS TEMPERATURE
CURVE IS SHOWN IN THE
FIGURE.
THE CURVES ARE
NEARLY LINEAR, AND
FOR SMALL
TEMPERATURE RANGE, IT
IS VERY EVIDENT.

39. CONSTRUCTION OF RESISTIVE
THERMOMETER
• The resistance thermometer is placed inside the protective tube for providing the
protection against damage.
• 2. The resistive element is formed by placing the platinum wire on the ceramic
bobbin.
• 3. This resistance element is placed inside the tube which is made up of stainless steel
or copper steel.
• 4. The lead wire is used for connecting the resistance element with the external lead.
• 5. The lead wire is covered by the insulated tube which protects it from short circuit.
• 6. The ceramic material is used as an insulator for high temperature material and for
low-temperature fiber or glass is used

41. OPERATION OF RESISTIVE THERMOMETER
• The tip of the resistance thermometer is placed near the measurand heat source. The
heat is uniformly distributed across the resistive element. The changes in the resistance
vary the temperature of the element. The final resistance is measured. The below
mention equations measure the variation in temperature:
• where Rθ – approximation resistance at θºC
• Rθ0 – approximation resistance at θ0 ºC
• Δθ – θ – θ0 change in temperature ºC
• αθ0 – resistance temperature coefficient at θ0 ºC

42. Advantages Disadvantages
1. The accuracy of RTD is good.
2. Temperature compensation is
not necessary.
3. The RTD available in wide
range.
4. The stability maintained over
long period of time.
5. It can be used to measure
differential temperature.
6. It is suitable for remote
indication.
7. It can be easily installed and
replaced.
1. The cost of RTD is high.
2. It has large bulb size.
3. Low sensitivity occurs in
RTD.
4. Affected by shock and
vibration.
5. Possibility of self heating.
6. Bridge circuit is needed
with power supply

43. THERMOCOUPLES
• Thermocouples are formed when two
dissimilar metals are joined together
to form a junction. An electrical
circuit is completed by joining the
other ends of the dissimilar metals
together to form a second junction. A
current will flow in the circuit if the
two junctions are at different
temperatures as shown in Fig.

44. THERMOCOUPLE
• A thermocouple is comprised of at least
two metals joined together to form two
junctions.
• One is connected to the body whose
temperature is to be measured; this is the
hot or measuring junction.
• The other junction is connected to a body
of known temperature; this is the cold or
reference junction.
• Therefore the thermocouple measures
unknown temperature of the body with
reference to the known temperature of
the other body.

45. THERMOCOUPLE: WORKING PRINCIPLE
• The working principle of thermocouple is based on three effects, discovered by
Seebeck, Peltier and Thomson. They are as follows:
• 1) Seebeck effect: The Seebeck effect states that when two different or unlike
metals are joined together at two junctions, an electromotive force (emf) is generated
at the two junctions. The amount of emf generated is different for different
combinations of the metals.
• 2) Peltier effect: As per the Peltier effect, when two dissimilar metals are joined
together to form two junctions, emf is generated within the circuit due to the
different temperatures of the two junctions of the circuit.

46. • 3) Thomson effect: As per the Thomson effect, when two unlike metals are
joined together forming two junctions, the potential exists within the circuit due to
temperature gradient along the entire length of the conductors within the circuit. In
most of the cases the emf suggested by the Thomson effect is very small and it can
be neglected by making proper selection of the metals. The Peltier effect plays a
prominent role in the working principle of the thermocouple.

47. THERMOCOUPLE: WORKING
• It comprises of two dissimilar metals, A and B. These are joined
together to form two junctions, p and q, which are maintained at the
temperatures T1 and T2 respectively.
• Remember that the thermocouple cannot be formed if there are not
two junctions.
• Since the two junctions are maintained at different temperatures the
Peltier emf is generated within the circuit and it is the function of the
temperatures of two junctions.

48. • If the temperature of both the junctions is same, equal and opposite
emf will be generated at both junctions and the net current flowing
through the junction is zero.
• If the junctions are maintained at different temperatures, the emf’s
will not become zero and there will be a net current flowing through
the circuit.
• The total emf flowing through this circuit depends on the metals used
within the circuit as well as the temperature of the two junctions.
• The total emf or the current flowing through the circuit can be
measured easily by the suitable device.

50. • The device for measuring the current or emf is connected within the circuit of the
thermocouple.
• It measures the amount of emf flowing through the circuit due to the two junctions of
the two dissimilar metals maintained at different temperatures.
• In figure 2 the two junctions of the thermocouple and the device used for measurement
of emf (potentiometer) are shown.
• Now, the temperature of the reference junctions is already known, while the
temperature of measuring junction is unknown.
• The output obtained from the thermocouple circuit is calibrated directly against the
unknown temperature.
• Thus the voltage or current output obtained from thermocouple circuit gives the value
of unknown temperature directly.

52. TYPES OF THERMOCOUPLE

53. BASE METAL THERMOCOUPLES– IN THIS CATEGORY OF THERMOCOUPLE,
THE BASE METAL IS MADE FROM COMMON AND INEXPENSIVE MATERIALS
SUCH AS NICKEL, IRON, COPPER.
• Following types fall under this category-
• Type K Thermocouple– It consists of Nickel-Chromium or Nickel-Alumel. It is most
commonly used. It is inexpensive and has a wide temperature range at the same time it
provides accuracy and reliability. It has the temperature range from -330 to 2300⁰F. Its
wire colour code is yellow and red.
• Type J Thermocouple– It consists of Iron/Constantan. It permits smaller temperature
range and has a shorter lifespan at a higher temperature. As oxidation problem is
associated with Iron, some precautions must be taken when using this type of
thermocouple in an oxidising environment. Its temperature range lies in between 32 to
1400⁰F and wire colour code is white and red.

54. • Type T Thermocouple– These consist of Copper/Constantan. This category of the
thermocouple is very stable and is used in very low-temperature applications such as in
cryogenics. The temperature range of type T Thermocouple lies in between -330 to
700⁰F and its wire colour code is blue and red.
• Type E Thermocouple– It is composed of Nickel-Chromium/Constantan. At moderate
temperature, it provides higher stability as compared to Type K and Type J. This type of
Thermocouple has the highest emf vs temperature values among all commonly used
Thermocouples. The temperature range is between -330 to 1600⁰F and wire colour code
is purple and red.
• Type N Thermocouple– It is composed of Nicrosil/Nisil. It is slightly expensive and
shares almost similar accuracy and temperature limits as that of K Type. The
temperature range lies in between 32 to 2300⁰F and wire colour code is orange and red.

55. NOBLE METAL THERMOCOUPLE– IT HAS THE ABILITY TO
WITHSTAND HIGH TEMPERATURE AND IS MADE UP OF
EXPENSIVE MATERIALS.
• Following types fall under this category-
• Type S Thermocouple– It is composed of Platinum Rhodium- 10%/ platinum. It is
mostly used in high-temperature applications. But can be used for lower temperature
applications due to high stability. It is mostly used in Biotech industries.
• Type R Thermocouple– These are composed of Platinum Rhodium-13%/ Platinum. It
is more expensive as it contains more percentage of Rhodium as compared to Type S.
Its performance is almost similar to that of Type S.
• Type B Thermocouple– These are composed of Platinum Rhodium- 30%/ Platinum
Rhodium-6%. It is known to be the highest temperature limit thermocouple among all
others. It provides the highest stability and accuracy at high temperature.

58. Advantages Disadvantages
1. The thermocouple is less
expensive than RTD.
2. It has wide temperature
ranges. 3. It has good
reproducibility.
4. The temperature range is
270 to 2700 degree Celsius.
5. It has rugged construction.
6. It does not required bridge
circuit.
7. It has good accuracy.
8. It has high speed of response
1. The stray voltage pick up is
possible.
2. As output voltage is very small, it
needs amplification.
3. The cold junction and lead
compensation is essential.
4. It shows non linearity

59. APPLICATIONS:
1. To monitor temperatures of liquids and gases in storage and flowing
pipes and ducts.
2. In industrial furnaces
3. For temperature measurement in cryogenic range.

60. SEMICONDUCTORS
• Semiconductors have a number of parameters that vary linearly with temperature.
• Normally the reference voltage of a zener diode or the junction voltage variations are used for
temperature sensing.
• Semiconductor temperature sensors have a limited operating range from –50 to 150°C but are very linear
with accuracies of ±1°C or better.
• Other advantages are that electronics can be integrated onto the same die as the sensor giving high
sensitivity, easy interfacing to control systems, and making different digital output configurations
possible.
• The thermal time constant varies from 1 to 5 s, internal dissipation can also cause up to 0.5°C offset.
• Semiconductor devices are also rugged with good longevity and are inexpensive. For the above reasons
the semiconductor sensor is used extensively in many applications including the replacement of the
mercury in glass thermometer.

61. TEMPERATURE RANGE AND ACCURACY OF
TEMPERATURE SENSORS

62. SUMMARY OF SENSOR CHARACTERISTICS

63. PYROMETERS
• All the temperature measuring methods studied earlier require physical contact of thermometer with the
body whose temperature is to be measured.
• But at high temperatures above 1400 °C, the thermometer may melt due to direct physical contact.
• To solve these problems, a non-contact method of temperature measurement is used. This method is also
suitable for moving bodies.
• Pyrometry is a technique for measuring temperature without physical contact.
• A pyrometer is a device that is used for the temperature measurement of an object.
• The device actually tracks and measures the amount of heat that is radiated from an object.
• The thermal heat radiates from the object to the optical system present inside the pyrometer.
• The optical system makes the thermal radiation into a better focus and passes it to the detector.
• The output of the detector will be related to the input thermal radiation.

64. • Pyrometer also is known as an Infrared thermometer or Radiation thermometer or
non-contact thermometer used to detect the temperature of an object’s surface
temperature, which depends on the radiation (infrared or visible) emitted from the
object. Pyrometers act as photodetector because of the property of absorbing energy
and measuring of EM wave intensity at any wavelength.
• These are used to measure high-temperature furnaces. These devices can measure
the temperature very accurately, precisely, pure visually and quickly. Pyrometers
are available in different spectral ranges ( since metals – short wave ranges and
non-metals-long wave ranges).

65. • Color pyrometers are used to measure the radiation emitted from the object during the
temperature measurement. These can measure the object’s temperature very accurately.
Hence the measuring errors are very low with these devices.
• Color pyrometers are used to determine the ratio of two radiation intensities with two
spectral ranges. These are available in series of Metis M3 and H3 and handheld
portables Capella C3 in different versions.
• High-speed pyrometers are used to temperature more fastly and quickly than M3
devices. These are available in combination with 1-color and 2-color pyrometers. These
devices can create clear temperature profiles of fast-moving objects and control the
adequate temperature level.

66. WORKING PRINCIPLE OF PYROMETER
• Pyrometers are the temperature measuring devices used to detect the object’s
temperature and electromagnetic radiation emitted from the object. These are
available in different spectral ranges. Based on the spectral range, pyrometers are
classified into 1-color pyrometers, 2-color pyrometers, and high-speed pyrometers
• The basic principle of the pyrometer is, it measures the object’s temperature by
sensing the heat/radiation emitted from the object without making contact with the
object. It records the temperature level depending upon the intensity of radiation
emitted. The pyrometer has two basic components like optical system and detectors
that are used to measure the surface temperature of the object.

67. STEFAN–BOLTZMANN LAW
• According to Stefan Boltzmann law, the amount of radiation emitted per unit time from
an area A of a black body at absolute temperature T is directly proportional to the
fourth power of the temperature.
• u/A = σT4 . . . . . . (1)
• where σ is Stefan’s constant = 5.67 × 10-8 W/m2 k4
• A body that is not a black body absorbs and hence emit less radiation, given by equation
(1)
• For such a body, u = e σ AT4 . . . . . . . (2)
• Where
• e = emissivity (which is equal to absorptive power) which lies between 0 to 1.
• With the surroundings of temperature T0, net energy radiated by an area A per unit
time.
• Δu = u – uo = eσA [T4 – T0
4] . . . . . . (3)

68. Figure - Stefan–Boltzmann law: power radiated by a greybody with
different emissivities.

69. WIEN'S DISPLACEMENT LAW
• Wien's displacement law states that the black-body radiation curve for different
temperatures will peak at different wavelengths that are inversely proportional to
the temperature. The shift of that peak is a direct consequence of the Planck
radiation law, which describes the spectral brightness of black-body radiation as a
function of wavelength at any given temperature.
• However, it had been discovered by Wilhelm Wien several years before Max Planck
developed that more general equation, and describes the entire shift of the spectrum
of black-body radiation toward shorter wavelengths as temperature increases.

70. • Wien's displacement law states that the spectral radiance of black-body radiation
per unit wavelength, peaks at the wavelength λpeak given by:
• where
• T is the absolute temperature.
• b is a constant of proportionality called Wien's displacement constant, equal
to 2.897771955...×10−3 m⋅K,or b ≈ 2898 μm⋅K
• This is an inverse relationship between wavelength and temperature. So the higher
the temperature, the shorter or smaller the wavelength of the thermal radiation.
The lower the temperature, the longer or larger the wavelength of the thermal
radiation.
• For visible radiation, hot objects emit bluer light than cool objects. If one is
considering the peak of black body emission per unit frequency or per proportional
bandwidth, one must use a different proportionality constant.

71. • However, the
form of the law
remains the
same: the peak
wavelength is
inversely
proportional to
temperature, and
the peak
frequency is
directly
proportional to
temperature.
Fig-Black-body radiation as a function of wavelength for various
temperatures. Each temperature curve peaks at a different
wavelength and Wien's law describes the shift of that peak.

72. • When any object is taken whose surface temperature is to be measured with the
pyrometer, the optical system will capture the energy emitted from the object. Then
the radiation is sent to the detector, which is very sensitive to the waves of
radiation. The output of the detector refers to the temperature level of the object due
to the radiation. Note that, the temperature of the detector analyzed by using the
level of radiation is directly proportional to the object’s temperature.

73. • The radiation emitted from every targeted object with its actual temperature goes
beyond the absolute temperature ( -273.15 degrees Centigrade ). This emitted
radiation is referred to as Infrared, which is above the visible red light in the
electromagnetic spectrum. The radiated energy is used for detecting the
temperature of the object and it is converted into electrical signals with the help of a
detector.

74. Pyrometer
Radiation
Pyrometer
Optical
Pyrometer

75. INFRARED OR RADIATION PYROMETERS
• These pyrometers are designed to detect thermal radiation in the infrared region,
which is usually at a distance of 2-14um.
• It measures the temperature of a targeted object from the emitted radiation. This
radiation can be directed to a thermocouple to convert into electrical signals.
Because the thermocouple is capable of generating higher current equal to the heat
emitted.
• Infrared pyrometers are made up of pyroelectric materials like polyvinylidene
fluoride (PVDF), triglycine sulfate (TGS), and lithium tantalate (LiTaO3)

76. Infrared or Radiation
Pyrometers

77. Advantages Disadvantages
•It can measure the
temperature of the object
without any contact with the
object. This is called Non-
contact measurement.
•It has a fast response time
•Good stability while
measuring the temperature of
the object.
•It can measure different
types of object’s temperature
at variable distances.
• Pyrometers are generally
rugged and expensive
• Accuracy of the device can
be affected due to the
different conditions like
dust, smoke, and thermal
radiation.

78. APPLICATIONS
Pyrometers are used in different applications such as,
• To measure the temperature of moving objects or constant objects from a greater
distance.
• In metallurgy industries
• In smelting industries
• Hot air balloons to measure the heat at the top of the ballon
• Steam boilers to measure steam temperature
• To measure the temperature of liquid metals and highly heated materials.
• To measure furnace temperature.

79. OPTICAL
PYROMETERS
• These are one of the types of pyrometers used to detect thermal radiation of the
visible spectrum.
• The temperature of the hot objects measured will depend on the visible light they
emit.
• Optical pyrometers are capable of providing a visual comparison between a calibrated
light source and the targeted object’s surface.
• When the temperature of the filament and the object’s surface is the same, then the
thermal radiation intensity caused due to the filament merges and into the targeted
object’s surface and becomes invisible. When this process happens, the current
passing through the filament is converted into a temperature level.

80. Optical
Pyrometers

81. Advantages Disadvantages
•1. The optical pyrometer is
useful for high
temperatures.
•2. It is useful for monitoring
the temperature of moving
object and distant objects.
•3. It has good accuracy.
•4. No need for contact with
target of measurement.
•5. It is light in weight.
1. The accuracy may be
affected by dust, smoke and
thermal background
radiation.
2. The optical pyrometer is
not useful for measuring the
temperature of clean
burning gases that do not
radiate visible energy.
3. It is more expensive.
4. It causes human errors.

82. WHAT WE HAVE LEARN TODAY
Expansion
Thermometer
Filled System
Thermometer
Electrical
Measurement
thermometer
Pyrometer
Temperature
Measuring
Devices

83. ANY QUESTIONS ?
Thank
You!!