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What is Thermocouple Wire Used for?

With the many different specialty wires and cables we sell at Arcor, you may be curious what our bare thermocouple wire is and what it’s used for. Thermocouple wire is made with two insulated wires of different metal alloys used specifically for thermocouple applications and is used to make or extend the signals of a thermocouple. But to understand what makes these such a special wire and cable, you need to understand how a thermocouple works.

What is a Thermocouple?

Thermocouples are a sort of sensor that is used to measure different temperatures, which is especially useful for measurement and control applications. The reason why specialty wire and cable must be used, thermocouple wire in this case, are because two different alloys must be used to achieve a thermoelectric effect.

In 1821, Thomas Johann Seebeck discovered that any conductor that is subjected to a thermal gradient will generate voltage. And when you attempt to measure this voltage with another conductor at the ‘hot’ end, the second conductor will generate its own voltage that opposes the original conductor. When using a different metal to complete this circuit, it creates a circuit with two different voltages being generated by the legs. This disparity in the voltage is what makes it possible to measure the temperature, as the difference in voltage increases with the temperature. That’s why it’s important for bare thermocouple wire to be made with two different metal alloys. These different voltages can then be fed back into a voltmeter, which can translate the voltage difference into the temperature of what was measured.

Why do Thermocouple Wires Come in Different Grades?

You may have also noticed that thermocouple wire comes in many different types. This is because the magnitude of the effect changes depending on the alloys being used in the thermocouple wire. Many thermocouple wiresuse constantan wire and a second alloy, such as iron or copper wire cables, in order to create the thermoelectric effect, but the types of wire used really depends on the needs of what temperatures you’re measuring.

That’s why you’ll see a letter type describing the thermocouple wire, which will tell you what materials it’s made from and what range it can accurately and safely measure. So type T will denote a copper wire and constantan wire are being used and can measure in the -200 to 350 °C range, while a type N will consist of a nicrosil wire and a nisil wire and perform between -270 °C and 1300 °C.