How Does A Thermocouple Work?
Measurement and control of
temperature is one of the most common requirements of
industrial instrumentation and the thermocouple is by far the
most widely used temperature sensor. Its characteristics include
good inherent accuracy, suitability over a broad temperature
range, fast thermal response, ruggedness, high reliability and
How does a thermocouple work?
T.J Seebeck discovered in the 1820s that an electric current
flows in a closed circuit of two dissimilar metals when one of
the two junctions is heated with respect to the other. In a
thermocouple circuit the current continues to flow as long as
the two junctions are at different temperatures. The magnitude
and direction of the current depends on the temperature
difference between the junctions and the properties of the
metals used in the circuit. This is known as the Seebeck effect.
here to see an example of the circuit.
If the circuit is broken at the center, the net open circuit
voltage (the Seebeck voltage) is a function of the junction
temperature and the composition of the two metals.
If the hot and cold junctions are reversed, current will flow in
the opposite direction. Any two dissimilar metals can be used
and the thermocouple circuit will generate a low voltage output
that is almost (but not exactly) proportional to the temperature
difference between the hot junction and the cold junction. The
voltage output is between 15 and 40