What is it?
A thermocouple is a device used extensively for measuring temperature.
What does it do?
It is comprised of two metal wires joined together to form two junctions. One is connected to the
body whose temperature is to be measured; this is the hot or measuring junction. The other junction
is connected to a body of known temperature; this is the cold or reference junction. The
thermocouple measures unknown temperature of the body with reference to the known temperature
of the other body.
How does it works?
One zone, where the temperature is being measured, is uniformly hot. Another, containing the
reference junction and instrument connections, is taken to be at a cooler, and likewise uniformly
ambient. And in between is a center zone within which the temperature is assumed to vary in a
linear manner with distance, decreasing smoothly from the hotter to the cooler temperature.
All thermoelectric activity takes place in the center zone of decreasing temperature. The
thermoelectric effect is an extended and continuous one that is distributed along the entire length
the two wires. The process is driven by the temperature differences, or gradients, through which
these wires pass.