Thermo Sensors Corp.

Industrial Thermocouples

The Principles and Features of Thermocouples

Today’s thermocouple designs are the result of many years of research and field experience. Together with quality instruments they provide the answer to thousands of temperature sensing and control problems.

The Seebeck Effect

Basically, a thermocouple is a closed circuit formed of two dissimilar metallic conductors to produce an electromotive force (EMF) or voltage. The voltage causes a current to flow when heat is applied to one of the junctions. The current will continue to flow as long as the two junctions are at different temperatures. This is called the Seebeck effect, after T. J. Seebeck who discovered the principle.

The direction of the current flow at the cooler of the two junctions (T1) determines polarity. For example, in Figure 2 when the current flows from a to B. a is considered positive.

The Pettier Effect

Peltier found that when current flows across the junction of two dissimilar metals the junction will either release heat or absorb it, depending on the direction the current is flowing. If the current flows in the same direction as the current produced in a thermocouple at the measuring junction, heat will be absorbed and heat will be released at the opposing (cold) junction. The amount of heat absorbed and released is proportional to the quantity of electricity flowing across the junction.