Thermocouples. What are they? What are they used for? How do they work? What are the different available styles? What types are most commonly used?
What are thermocouples?
Thermocouples are simple and cost-effective temperature sensors used in a wide range of temperature measurement processes.
What are thermocouples used for?
Because of their low cost, high temperature limits, wide temperature ranges, and durable nature, thermocouples are used in many industrial, scientific and OEM applications found in nearly all markets, such as power generation, oil production, automotive research and development, and pharmaceutical to name a few.
Thermocouples are also used in everyday appliances including stoves, furnaces, and toasters.
Thermocouples are very simple sensors consisting of specific conductors, conductor insulation and protection appropriate for the temperature and environment they’re needed for.
How do thermocouples work?
It’s a matter of physics and the result of a thermoelectric effect known as the Seebeck effect, named after Thomas Johann Seebeck, a German physicist. In 1821 Seebeck discovered that an electric current flows between two dissimilar conductive materials that are kept at different temperatures, as a result of an electromotive force (EMF).
It’s this effect that is responsible for the behavior of thermocouples.
A typical thermocouple is made up of two dissimilar metal wires, joined together at one end to form two junctions.
One junction is placed on the surface or in the environment that is being measured. This is called the “hot” junction.
The other junction remains at a known constant temperature, which is the “cold” junction.
By changing the temperature of the hot junction, a voltage will flow through the loop.
Based on the differential in temperatures between the hot and cold junctions, a formula can be created that converts the voltage into a temperature reading.
What are different styles of thermocouples and what types are most commonly used?
Known for their versatility, thermocouples are manufactured in a variety of styles engineered to suit the application.
The most commonly used thermocouple calibration types are K, J, T and E that use Base Metals, which are nonferrous, or no iron metals like copper, iron, nickel, and aluminum.
Types R, S, B, and C are other types of thermocouples that utilize Nobel Metals, like platinum, rhodium, and rhenium which resist oxidation and can be used in higher temperature applications.
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