Thermocouples are transducers that convert heat directly into electricity according to the Seebeck effect. They consist of two conductors welded together at one end to form a junction, with the voltage difference between the junctions proportional to the temperature difference. The main types are K, J, T, E, N, S, B, and R, which differ in temperature range and sensitivity. Thermocouples are used to measure temperature and generate power due to their ruggedness, low cost, and ability to function over a wide range of temperatures. However, they also have low accuracy and can be vulnerable to corrosion.

1. THERMOCOUPLE
as a
TRANSDUCER

2. Outline
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 Introduction
 Principle
 Description
 Types
 Applications
 Advantages
 Disadvantages

3. Transducer
variations in a
physical quantity
another physical
quantity in
measurable form
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Transducers are used in instrumentation systems to
interface physical quantities with analytical ones.

4. Thermocouple
• A thermoelectric transducer that converts
heat directly into electricity, according to
the Seebeck effect.
• This can be used to generate electricity,
measure temperature difference or change
the temperature of objects.
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5. The Seebeck Effect
temperature
difference between
two junctions
voltage difference
between them
which drives the
current
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Eemf = - S T
where, S is the Seebeck coefficient
= T1 – T2

6. Basic Thermocouple Circuit
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If the SA and SB are constant for the
given temperature range, then
From Seebeck effect, the voltage
gradient at any point in the circuit,
Total measured end-to-end voltage
between the junctions,
Vb -Vc = (SA – SB) (Th -Tc )
= SAB (Th -Tc )

7. How it looks like ?
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Its construction consists of two conductors, welded together at the measuring point
and insulated from each other along the length, inside an outer protection sheath.

8. Types of Thermocouples
Type K : Chromel-Alumel
Type J : Iron-Constantan
Type T : Copper-Constantan
Type E : Chromel-Constantan
Type N : Nicros-Nisil
Type S : Platinum-Rhodium
Type B : Platinum-Rhodium
Type R : Platinum-Rhodium
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There are many thermocouples, but only 8 of them are standardized internationally.
BASE METAL NOBLE METAL
Each thermocouple type has a specific range of temperature and environment.

9. Thermocouple EMF vs Temperature
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This shows that the various thermocouples differ in their respective sensitivities.

10. Applications
• Temperature Measurement
• Power Generation
• Radiation Sensors
• Gas Safety Equipments
• Manufacturing Industry
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11. Advantages
• Rugged
• Inexpensive
• Quick response time
• Very simple in construction
• Used to measure temperature ranges
spanning thousands of degrees, around
-200 C to 2200 C
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12. Disadvantages
• Low accuracy
• Vulnerable to corrosion
• Thermocouple operation is relatively
complex with potential sources of error
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13. THANK YOU
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