A thermocouple, which is a type of industrial thermometer, is used to measure extreme temperatures. The properties of thermocouples were originally discovered in 1822 by Thomas Seebeck. Temperature differences that the thermocouple measures result from thermoelectric voltage differences produced by the two dissimilar metals that make up a thermocouple.
Thermocouples provide measurement over a large temperature range--from 200 to 2600 degrees Celsius. This allows thermocouples to be used in a variety of circumstances in different industries. Their vast temperature range also allows them to be used at high temperatures where most temperature gauges do not work.
Another advantage of thermocouples is they have the ability to be brought into direct contact with the material they are measuring. Since they use voltage readings to measure temperatures, the only requirement when bringing thermocouples in direct contact with the material being measured is ensuring the thermocouple is safely grounded.
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Since thermocouples are made up of two dissimilar metals, they are vulnerable to corrosion, which can sometimes be difficult to detect. Any type of light corrosion can result in a misreading by the thermocouple; therefore, proper care and maintenance of thermocouples is essential.
The correct calibration of thermocouples can be tedious and difficult. It is always essential thermocouple calibration be done next to another--already calibrated--thermocouple. During the calibration bath, the output is not reproduced exactly as it was, making correct calibration essential.
Thermocouples are complex and have many sources of error. This is mostly due to their operation. Thermocouples use two dissimilar metals that have two different voltage readings produced from a change in temperatures on alternative ends of the metals. They also have a cold junction, which consists of copper wires to allow the metal to meet the instrumentation. They use various types of electronic compensation at the cold junction to allow for more accurate readings; this accounts for marginal errors, depending upon the type of thermocouple used.