Thermocouple as a Transducer ppt

Amity School of Engineering & Technology
Thermocouple as
a Transducer
By
Aniket Shrivatava
B.Tech (ME), V Semester
Mechanical Engineering Department
1

Content
 Introduction.
 Definition of Thermocouple.
 Working Principle of Thermocouple.
 Construction of Thermocouple.
 Working of Thermocouple.
 Measurement of Thermocouple Output.
 Advantages of Thermocouple.
 Disadvantages of Thermocouple.
 Application of Thermocouple.
2

Introduction
 In the year 1821, a physicist namely “Thomas Seebeck” revealed
that when two different metal wires were linked at both ends of one
junction in a circuit when the temperature applied to the junction,
there will be a flow of current through the circuit which is known as
electromagnetic field (EMF). The energy which is produced by the
circuit is named as the Seebeck Effect. Using Thomas Seebeck’s
effect as his guideline, both Italian physicists namely Leopoldo
Nobili and Macedonio Melloni were collaborated to design a
thermoelectrical- battery in the year 1826, that is called as a thermal
multiplier, it drew from the discovery of Seebeck’s thermoelectricity
by merging a galvanometer as well as a thermopile to calculate
radiation. For his effort, some people identified Nobili as the
discoverer of the thermocouple.
3

Definition of Thermocouple
 The thermocouple is a temperature measuring device. It uses
for measuring the temperature at one particular point. In other
words, it is a type of sensor used for measuring the
temperature in the form of an electric current or the EMF.
 The thermocouple consists two wires of different metals which
are welded together at the ends. The welded portion was
creating the junction where the temperature is used to be
measured. The variation in temperature of the wire induces the
voltages.
4

Working Principle of Thermocouple
The working principle of the thermocouple depends on
the three effects.
 Seeback Effect – The See back effect occurs between two
different metals. When the heat provides to any one of the
metal, the electrons start flowing from hot metal to cold metal.
Thus, direct current induces in the circuit.
 In short, it is a phenomenon in which the temperature
difference between the two different metals induces the
potential differences between them. The See beck effect
produces small voltages for per Kelvin of temperature..
5

 Peltier Effect – The Peltier effect is the inverse of the
Seebeck effect. The Peltier effect state that the temperature
difference can be created between any two different
conductors by applying the potential difference between them.
 Thompson Effect – The Thompson effect state that when
two dissimilar metals join together and if they create two
junctions then the voltage induces the entire length of the
conductor because of the temperature gradient. The
temperature gradient is a physical term which shows the
direction and rate of change of temperature at a particular
location.
6

Construction of Thermocouple
The thermocouple consists two dissimilar metals. These
metals are welded together at the junction point. This
junction considers as the measuring point. The junction point
categorizes into three types
1. Ungrounded Junction – In ungrounded junction, the
conductors are entirely isolated from the protective sheath. It
is used for high-pressure application works. The major
advantage of using such type of junction is that it reduces the
effect of the stray magnetic field.
7

2. Grounded Junction – In such type of junction the metals
and protective sheath are welded together. The grounded
junction use for measuring the temperature in the corrosive
environment. This junction provides resistance to the noise.
3. Exposed Junction – Such type of junction uses in the
places where fast response requires. The exposed junction is
used for measuring the temperature of the gas.
8

9
The material uses for making the thermocouple depends on the
measuring range of temperature.

Working of Thermocouple
The circuit of the thermocouple is shown in the figure below. The
circuit consists two dissimilar metals. These metals are joined
together in such a manner that they are creating two junctions.
The metals are bounded to the junction through welding.
10

 Let the P and Q are the two junctions of the thermocouples.
The T1 and T2 are the temperatures at the junctions. As the
temperature of the junctions is different from each other, the
EMF generates in the circuit.
 If the temperature at the junction becomes equal, the equal and
opposite EMF generates in the circuit, and the zero current
flows through it. If the temperatures of the junction become
unequal, the potential difference induces in the circuit. The
magnitude of the EMF induces in the circuit depends on the
types of material used for making the thermocouple. The total
current flowing through the circuit is measured through the
measuring devices.
11

12
 The EMF induces in the thermocouple circuit is given by the
equation.
 Where Δθ – temperature difference between the hot
thermocouple junction and the reference thermocouple
junction.
 a, b – constants.

Measurement of Thermocouple Output
The output EMF obtained from the thermocouples can be measured
through the following methods.
1. Multimeter – It is a simpler method of measuring the output
EMF of the thermocouple. The multimeter is connected to the
cold junctions of the thermocouple. The deflection of the
multimeter pointer is equal to the current flowing through the
meter.
2. Potentiometer – The output of the thermocouple can also be
measured with the help of the DC potentiometer.
3. Amplifier with Output Devices – The output obtains
from the thermocouples is amplified through an amplifier and
then feed to the recording or indicating instrument.
13

Advantages of Thermocouple
The following are the advantages of the thermocouples.
 The thermocouple is cheaper than the other temperature
measuring devices.
 The thermocouple has the fast response time.
 It has a wide temperature range.
14

Disadvantages of Thermocouple
The following are the disadvantages of the
thermocouples.
 The thermocouple has low accuracy.
 The recalibration of the thermocouple is difficult.
Nickel-alloy, platinum/rhodium alloy, Tungsten/rhenium-alloy,
chromel-gold, iron-alloy are the name of the alloys used for making
the thermocouple.
15

Application of Thermocouple
Some of the applications of thermocouple include the
following.
 These are used as the temperature sensors in thermostats in
offices, homes, offices & businesses.
 These are used in industries for monitoring temperatures of
metals in iron, aluminum, and metal.
 These are used in the food industry for cryogenic and Low-
temperature applications. Thermocouples are used as a heat pump
for performing thermoelectric cooling.
 These are used to test temperature in the chemical plants,
petroleum plants.
 These are used in gas machines for detecting the pilot flame.
16

THANK YOU
17

Thermocouple as a Transducer ppt

More Related Content

What's hot (20)

Similar to Thermocouple as a Transducer ppt (20)

Recently uploaded (20)

Thermocouple as a Transducer ppt