A thermocouple is an electrical device consisting of two dissimilar metals joined together that produces a voltage dependent on the temperature difference between the junctions. Thermocouples operate based on the Seebeck effect and Peltier effect to measure a wide range of temperatures from -270°C to 3000°C. They are commonly used to monitor temperatures in industrial processes like kilns but are less accurate than other sensors for measuring small temperature differences with high precision.

1. Made by:- Patel Dhrumil R

2. Introduction
 A thermocouple is an electrical device consisting of two
dissimilar electrical conductors forming electric junction at
differing temperatures. A thermocouple produces a
temperature-dependent voltage as a result of the
thermoelectric effect , and this voltage can be interpreted to
measure temperature. Thermocouples are a widely used type
of temperature sensor.

3. Types of Thermocouple

4. Thermocouple

5. Working Principal
 If two wire of different metals M1 and M2 are joined together
to form a loop (thermocouple) as shown in Fig. with one
junction at temperature T1 and other at temperature T2, an
e.m.f. is generated and if an ammeter is connected , a current
flows in the circuit. This phenomenon is called seeback effect.
The magnitude of emf generated depends on the temperature of
the junction T1 and T2 and the material of M1 and M2. one of
the two junction is usually maintained at some constant known
temperature. The output voltage of the circuit then indicates the
temperature difference relative to the reference temperature .
Normally , the ice point of water(0c) is selected as are
reference junction.

7. Thermocouple effects
 Peltier effect:
 The temperatures T1 and T2 of junctions slightly
change if the thermoelectric current is allowed to flow
in the circuit.
 Heat is generated at cold junction and is absorbed from
the hot junction thereby heating the cold junction
slightly and cooling the hot junction slightly.
 This phenomenon is called Peltier effect.
 This effect takes place whether the current is
introduced extremely or is induced by the thermocouple
itself.

8. Thermocouple effects
 Thomson effect : The junction emf may be slightly
changed if the temperature gradient exist along either or
both the materials. This phenomenon is called Thomson
effect.

9. Application
 Thermocouples are suitable for measuring over a large
temperature range, from −270 up to 3000 °C (for a short time,
in inert atmosphere). Applications include temperature
measurement for kilns, gas turbine exhaust, diesel engines,
other industrial processes and fog machines. They are less
suitable for applications where smaller temperature differences
need to be measured with high accuracy, for example the range
0–100 °C with 0.1 °C accuracy. For such applications
thermistors , silicon bandgap temperature sensors and
resistance thermometers are more suitable.

10. Thank you