General description of Thermocouples which are a type of thermo-electric Transducer.

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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