How A Thermocouple Works - Omega Engineering 8 Channel Thermocouple USB Data Acquisition Module TC-08 User Manual

6 TC-08 User's Guide
2.2

How a thermocouple works

In a closed circuit of two dissimilar metals (a thermocouple), an electric current flows
when one of the two junctions is heated with respect to the other. The current
continues to flow as long as the two junctions are at different temperatures. The
magnitude and direction of the current is a function of the temperature difference
between the junctions and of the thermal properties of the metals used in the circuit.
This phenomenon is known as the Seebeck Effect.
The conductors can be made of any two dissimilar metals, and when the hot junction
is heated the current flow can be observed. If the positions of the hot and cold
junctions are reversed, current flows in the opposite direction.
A thermocouple circuit actually generates a measurable, low-voltage output that is
almost directly proportional to the temperature difference between the hot junction
and the cold junction. A change in this temperature difference produces some net
change in the voltage.
Note: More information on choosing and using thermocouples can be found at
www.omega.com.