A thermo couple works on the principle of thermoelectricity discovered by Seebeck. When two different conductors are joined at one end to form a junction and that junction is heated, a voltage is generated between the free ends. The magnitude of this voltage depends on the temperature difference between the junctions and the materials used. A thermo couple has a hot junction placed at the point of temperature measurement and a cold junction kept at a constant reference temperature. Connecting the free ends to a voltmeter allows measurement of the voltage, and thus the temperature. Connecting multiple thermo couples in series creates a thermopile, increasing sensitivity by summing the individual voltages.

1. THERMOCOUPLE
II ECE

2. PRINCIPLE:
The principle of thermo electricity which was discovered by Seeback.
It says “when 2 conductors of two different metals A & B are joined together at
one end to form a junction , and this junction is heated to higher temperature with
respect to the free ends, a voltage is developed at the free ends & if these 2
conductors of metals at the free ends are connected , then the emf setup will
establish a flow of current.”
 The magnitude of the net emf will depend upon the magnitude between the
temperature of the two junctions and the materials used for the conductors.

6. CONSTRUCTION:
• There are 2 junctions:
Thermocouple hot junction JH – intoduced into the plce where the
temperature is to be measured.
Thermocouple cold junction JC- maintained at a constant reference
temperature.
• A voltage measuring instrument (millivoltmeter) is connected to
the free ends of thermocouple.

7. OPERATION:
• Thermocouple hot junction JH introduced to the place where
temperature is to be measured.
• Reference temperature is controlled to be at a constant temperature
at 0°C.
• As the 2 junctions are at different temperatures , a voltage is setup
at the free ends which will establish a flow of current which can be
directly measured using the millivoltmeter connected across the
free ends.

8. THERMOPILE
• Thermocouples connected in series form thermopile.
• These are used to measure small temperature differences between the two
junctions.
• The series arrangement increases sensitivity and gives a large output even for a small
temperature difference.
• In series arrangement , total emf is the sum of emfs developed by individual
thermocouples .
When n thermocouples are connected in series , the total emf is
E=E1+E2+E3+….+En
But all thermocouples are similar and they work under similar conditions
Therefore , E1 = E2 = E3 = ….. = En , i.e, E = nE1 ,which means resulting emf is n times
the emf of an individual thermocouple.

9. THERMOCOUPLES CONNECTED IN PARALLEL
• When average temperature measurement is to be done,
thermocouples are connected in parallel.
• Total emf is:
E = (E1+E2+E3)/3

10. THANK YOU