Though they are working constantly around us, not many people really understand the basic different thermocouple types or what they are actually used for. Thermocouples, which are often referred to as TCs, are used in ordinary devices everywhere. It may be surprising to find how strange our lives would really be without presence. From our home furnaces and hot water heaters to our automobiles, our lives would be vastly different without their use.
Basically a TC is a form of sensor which measures temperature and overall temperature differences in devices. The principle which they are based is that as 2 dissimilar metals are linked there is a relative amount of voltage which is produced. This voltage is related to what the temperature difference of whatever 2 metals the TC is made of. Building on this idea, there are several different types of TCs depending on what their use is.
Type K is constructed from alumel and chromel. It is often used for the general use and all purpose units. It has a very low cost for its construction and can be found being used various kinds of probe sensors. Its sensitivity range is from -200 C to about +1200 degrees C.
Type E is made from chromel and constantan. Because of its higher than average output is best suited for very cold temperature applications. It is also noted for being non magnetic. Its opposite is type B made from platinum and rhodium. Because of the voltage output curve it is best suited for temperatures up to 1800 degrees C.
Type N's are made using nicrosil and nisil. It is known for having high stability and having a superior resistance to higher temperature oxidation. As it is not built with platinum the production cost is much lower and this makes it the unit of choice for high temperature applications. Originally designed to be the replacement for most types K's it is being used for more and more everyday applications.
The type R and the type S are both constructed with rhodium and platinum. Because they use platinum for constructing them they have a production cost that is higher than average. The type R's are used for temperatures of 1600 deg C. The S's are used for temperatures of 1600 deg also. The typical use for a type S is in melting gold, where the melting point is around 1064 deg C.
Type J is constructed from constantan and iron. It also has a limited temperature range at 40 deg C to about +750 deg C. Due to the limited operational range it has it has become less popular than the type K. It is often used with older equipment that can not be adapted to more modern TCs.
This is a basic look at the more common of the thermocouple types and the things they are used for. Even though it seems their name makes them sound very complex or rare, nothing could possibly be further from the truth. When you take a nice hot shower just relax, your water heater's thermocouple has been working quietly to keep the water hot every hour of every day.
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