Thermocouples are used in water heating systems.
Thermocouples are electronic devices that are used to monitor and control temperature. Thermocouples consist of two different types of metals joined together. When one of the pieces of metal is at a different temperature to the other an electrical current flows between the two pieces of metal. This is called the Seebeck effect.
The Home Body Class
Home body class thermocouples use pairs of relatively common metals. The different subtypes of the home body class are designated by letters. Type C thermocouples use two tungsten rhenium alloys, with one side having 5 percent rhenium and 95 percent tungsten and the other 26 percent rhenium and 74 percent tungsten. Type C thermocouples are useful for temperature ranges of up to 4,200 degrees Fahrenheit. Type E thermocouples use chromel and constantan and are useful for temperature ranges between 200 and 1,650 degrees Fahrenheit. Type J use iron and constantan and are useful for temperatures between 200 and 1,400 degrees Fahrenheit. Type K uses chromel and alumel and are used for temperatures between 200 and 2,300 degrees Fahrenheit.
The Rarefied Class
The rarefied class of thermocouples uses refractory metals. Refractory metals are found around the middle of the periodic table and are remarkable for their extreme resistance to wear and heat. It is these properties that makes rarefied class thermocouples so useful in specific applications. An example of the use of rarefied class thermocouples is in the measuring of temperatures in nuclear power plants.
The Upper Crust Class
The upper crust class of thermocouples includes any thermocouples that have platinum as one of the metals in the pair. As with the home body class they are divided into subtypes by letter. These subtypes are type B, with one of the pair being a 70-percent-platinum and 30-percent-rhodium alloy and the other being a 94-percent-platinum and 6-percent-rhodium alloy; these are used for temperature ranges between 2,500 and 3,100 degrees Fahrenheit. Type R and type S both have a platinum rhodium alloy for one of the pair and pure platinum for another. Type R and type S are used for temperature ranges between 1,600 and 2,640 degrees Fahrenheit and 1,800 and 2,640 degrees Fahrenheit respectively.
The Exotic Class
The exotic class of thermocouples include many thermocouples made from tungsten, but are not widely used in industry. They mainly include advanced experimental thermocouples in development in universities and research institutions.
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