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The Thermocouple - A Device Used to Measure Temperature


The Thermocouple

A temperature sensor is a device used to measure temperature through an electrical signal that requires a thermocouple. This electronic device consists of two dissimilar conductors (different types of metals) joined together at one end, which form electrical junctions at varying temperatures. When the junction of the conductors is heated or cooled, it emits a temperature dependent voltage formed by a thermoelectric effect, which can be used to measure temperature.

German physicist Thomas Seebeck has been credited with discovering the thermoelectric effect. He found that if two ends of a metal were sitting at different temperatures, an electric current would flow through it. He later realized that if he connected the two ends of the metal together, no current flowed. Coincidently, no current flowed if the two ends of the metal were at the same temperature. Seebeck finally used two different metal conductors and found that an electrical current was flowing through. Electrical conductivity paired with thermal conductivity is the sole proprietor in determining how well an electrical current will flow. Thus, the thermoelectric effect was discovered.

Electrons tend to move more freely in certain materials as opposed to others. This is the main difference between conductors and insulators. If you were to connect two different metals together (copper and iron), free electrons will move from one material to the other through a diffusion process. Electrons would move from the iron to the copper, resulting in the copper being more negatively charged and the iron being more positively charged. If one of the junctions was hotter than the other, electrons will readily diffuse between the metals. This means that the voltage at the two junctions will vary depending on their temperature difference.

There are many types of thermocouples such as: type K, J, T, E, N, S, R, B. Type K is the most common and has a wide temperature range. Another thermocouple that’s used frequently is Type J, which, displays a smaller temperature range. For extremely low temperatures, Type T should be used. Type E has a stronger signal and accuracy than Type K at moderate temperature ranges. Type N is a stronger and more expensive version of type K. In scenarios that have high temperatures, use Type S as it is very accurate and stable. Type R is used in high temperature applications and is constructed with a higher percentage of Rhodium. The thermocouple that can process the highest temperatures is Type B. One advantage of Type B is that it maintains a high level of accuracy.

There are some disadvantages of thermocouples. They have a tedious re-calibration system and are a bit difficult to verify. They are also susceptible to electromagnetic interference, also known as radio-frequency interference and can also be costly when trying to repair.

At AFR Enterprises, owned and operated by ASAP Semiconductor, we can help you find all your thermocouple parts for the aerospace, civil aviation, and defense industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@afrenterprises.com or call us at +1-714-705-4780.


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