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Thermocouple

The document provides an overview of thermocouples, which are temperature sensors that generate an electromotive force (e.m.f.) when subjected to temperature differences between two junctions made of dissimilar metals. It explains the working principle based on the Seeback Effect, advantages such as high accuracy and robustness, and disadvantages like nonlinearity and low sensitivity. Additionally, it outlines various applications of thermocouples in industries, thermostats, and temperature monitoring.

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15 views4 pages

Thermocouple

The document provides an overview of thermocouples, which are temperature sensors that generate an electromotive force (e.m.f.) when subjected to temperature differences between two junctions made of dissimilar metals. It explains the working principle based on the Seeback Effect, advantages such as high accuracy and robustness, and disadvantages like nonlinearity and low sensitivity. Additionally, it outlines various applications of thermocouples in industries, thermostats, and temperature monitoring.

Uploaded by

sreejith KB
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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INFORMATION SHEET

TRADE : I.Mech OUTCOME No: LESSON No:


DATE : TIME :

TITLE : Thermocouple

OBJECTIVES/TOPICS : At the end of this lesson you shall be able to

• Explain the construction and working of Thermocouple.

Descriptions:

Thermocouple:
Thermocouple is temperature sensor. Thermocouple produces EMF on experiencing a
temperature change. Thermocouples are called as transducers since it converts the
temperature into electrical energy. Since thermocouples do not any external energy for
the conversion of temperature to electrical output it is called active transducer.
Principle:
The thermocouple working principle is based on the Seeback Effect. This effect states
that when a closed circuit is formed by jointing two dissimilar metals at two junctions,
and junctions are maintained at different temperatures then an electromotive force
(e.m.f.) is induced in this closed circuit. The amount of induced e.m.f. is different for
different metal combinations and is proportional to the temperature difference of the
junctions. This is the basic thermocouple working principle.
Working:
When these junctions are kept at different temperatures, generally cold junction is kept
at 0oC and measuring junction is kept at an unknown temperature which we want to
measure (i.e. the temperature of the junction is raised by heating it). An e.m.f. will be
generated in this circuit due to the temperature difference of the junctions. This e.m.f.
is in the order of millivolts. And the e.m.f. can be measured with the help of a PMMC
instrument by connecting it in the circuit.
When both the junctions are at the same temperature, e.m.f. generated at both junctions
will be the same. No current will flow through the circuit. And there will be no
deflection in the meter. When both the junctions are at different temperatures, a current
will flow through the meter.

And the meter will show the deflection. As the generated e.m.f. is proportional to the
temperature difference, the amount of current flow will also be proportional to the
temperature difference. And therefore, the meter can be calibrated directly in terms of
temperature.

Advantages:
1. Accuracy is high
2. It is Robust and can be used in environments like harsh as well as high vibration.
3. The thermal reaction is fast
4. The operating range of the temperature is wide.
5. Wide operating temperature range
6. Cost is low and extremely consistent
Disadvantages:
1. Nonlinearity
2. Least stability
3. Low voltage
4. Reference is required
5. least sensitivity
6. The thermocouple recalibration is hard
Thermocouple Applications:
1. These are used as the temperature sensors in thermostats in offices, homes,
offices & businesses.
2. These are used in industries for monitoring temperatures of metals in iron,
aluminum, and metal.
3. These are used in the food industry for cryogenic and Low-temperature
applications. Thermocouples are used as a heat pump for performing
thermoelectric cooling.
4. These are used to test temperature in the chemical plants, petroleum plants.
5. These are used in gas machines for detecting the pilot flame.

Questions:-

REFERENCE :-

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