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thermocouple

ther·mo·cou·ple / ˈ[unvoicedth]ərmōˌkəpəl/ • n. a thermoelectric device for measuring temperature, consisting of two wires of different metals connected at two points, a voltage being developed between the two junctions in proportion to the temperature difference.

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thermocouple

thermocouple: see thermometer; thermoelectricity.

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"thermocouple." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 15 Nov. 2018 <https://www.encyclopedia.com>.

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Thermocouple

Thermocouple

Thermocouples, in electronics, are instruments used as temperature sensors. They are primarily used to show electric potential difference. Accurately measuring temperatures over a wide range is a challenge to engineers, physicists, and other scientists. Many techniques have been devised to deal with a wide range of conditions and temperatures. One such technique is a thermocouple. A thermocouple makes use of one aspect of the thermoelectric effect to measure temperatures. That aspect involves the voltage produced between two different wires with junctions at different temperatures. Depending on the types of wires chosen, a thermocouple can be used for temperatures ranging from 454°F to 4,172°F(270°C to 2,300°C).

A thermocouple must consist of two wires of different compositions. A popular combination is copper and constantan. Constantan is an alloy of copper and nickel. The different wires are joined at the ends to make two junctions. One of the wires is then cut so that a voltmeter can be placed in the circuit to measure the voltage between the two junctions. This voltage will depend on the temperature difference between the two junctions. A scientist wanting to use a thermocouple will then place one of the junctions in the object whose temperature is to be measured. Because the voltage depends on the temperature difference between the two junctions, the other junction must be maintained at an accurately known temperature. One way to maintain a known temperature is to place the junction in an ice water bath that will be at the freezing point of water. To find the unknown temperature, the scientist must know what temperature difference corresponds to the measured voltage. These figures have been determined by careful experiments and then they have been tabulated on a table. Therefore, the scientist can use the table to find the unknown temperature.

What causes this voltage difference? The two different types of metal, having different compositions, will have different densities of electrons. The electrons will tend to diffuse from the higher to the lower densities. These electron densities both depend on the temperature, so if the two junctions are at different temperatures the diffusion of electrons will proceed at different rates at each junction. The net result is a motion of the electrons, so there is a voltage between the two junctions.

Thermocouples are inexpensive to use. However, one of the biggest limitations of thermocouples is that accuracies of less than 1°C are difficult to maintain. They also have the advantage of being accurate over a wide temperature range and of being able to accurately follow rapid temperature changes. They can, however, be cumbersome to use. The need to keep one junction at an accurately known temperature limits their portability. Thermocouples, for example, are used quite often in the iron and steel industries. There are several different types of thermocouples. Type B (made with platinum-rhodium), Type S (platinum with 10% rhodium), Type R (platinum with 7% rhodium), and Type K (chromel [nickel-chromium alloy] and alumel [nickel-aluminum alloy]) thermocouples are used most often in steel and iron production due to their ability to monitor a wide range of temperatures throughout the long steel making process.

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Thermocouple

Thermocouple

Accurately measuring temperatures over a wide range is a challenge to engineers, physicists, and other scientists. Many techniques have been devised to deal with a wide range of conditions and temperatures. One such technique is a thermocouple. A thermocouple makes use of one aspect of the thermoelectric effect to measure temperatures, the voltage produced between two different wires with junctions at different temperatures. Depending on the types of wires chosen, a thermocouple can be used for temperatures ranging from -454°F to 4,172°F (-270°C to 2,300°C).

A thermocouple must consist of two wires of different compositions. A popular combination is copper and constantan. Constantan is an alloy of copper and nickel. The different wires are joined at the ends to make two junctions. One of the wires is then cut so that a voltmeter can be placed in the circuit to measure the voltage between the two junctions. This voltage will depend on the temperature difference between the two junctions. A scientist wanting to use a thermocouple will then place one of the junctions in the object whose temperature is to be measured. Because the voltage depends on the temperature difference between the two junctions, the other junction must be maintained at an accurately known temperature. One way to maintain a known temperature is to place the junction in an ice water bath that will be at the freezing point of water. To find the unknown temperature the scientist must know what temperature difference corresponds to the measured voltage. These figures are determined by careful experiments and then tabulated, so the scientist uses the table to find the unknown temperature.

What causes this voltage difference? The two different types of metal , having different compositions, will have different densities of electrons. The electrons will tend to diffuse from the higher to the lower densities. These electron densities both depend on the temperature, so if the two junctions are at different temperatures the diffusion of electrons will proceed at different rates at each junction. The net result is a motion of the electrons, so there is a voltage between the two junctions.

Thermocouples have the advantage of being accurate over a wide temperature range and of being able to accurately follow rapid temperature changes. They can however be cumbersome to use. The need to keep one junction at an accurately known temperature limits their portability.

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"Thermocouple." The Gale Encyclopedia of Science. . Encyclopedia.com. 15 Nov. 2018 <https://www.encyclopedia.com>.

"Thermocouple." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 15, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/thermocouple

"Thermocouple." The Gale Encyclopedia of Science. . Retrieved November 15, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/thermocouple

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Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

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American Psychological Association

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Notes:
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  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.