| A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert heat into electric power. They are inexpensive and interchangeable, are supplied fitted with standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy: system errors of less than one degree Celsius (C) can be difficult to achieve.
A thermocouple can produce current, which means it can be used to drive some processes directly, without the need for extra circuitry and power sources. The electrical energy generated by a thermocouple is converted from the heat energy must be supplied to the hot side to maintain the electric potential. A continuous flow of heat is necessary because the current flowing through the thermocouple tends to cause the hot side to cool down and the cold side to heat up (the Peltier effect).
Thermocouples measure the temperature difference between two points, not absolute temperature. To measure a single temperature one of the junctions normally the cold junction is maintained at a known reference temperature, and the other junction is at the temperature to be sensed.
Thermocouples are suitable for measuring over a large temperature range, up to 2300 °C. They are less suitable for applications where smaller temperature differences need to be measured with high accuracy, for example the range 0–100 °C with 0.1 °C accuracy. Applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes. |