The Thermocouple is the most universal, expedient, and versatile device used to measure temperature. It is a sensor that measures precise temperature within a wide range. Manufactured by joining together two dissimilar metals at one end, the thermocouple alloys are usually in the form of wire. A reference junction is also included at the opposite ends of the parent material. By heating or cooling the junction between dissimilar metals, a temperature gradient is produced, which generates a voltage. This voltage is converted into units of heat calibration at the ends of thermocouple wires. The heat generated is converted into useable units that serve as input signals for controllers. Thermocouples are suitable to be used in temperature ranges from -200 to 2316 °C [-328 to 4200] °F. Widely used in high-temperature applications, they are less expensive in most cases and can withstand higher temperatures than RTDs.
Life of thermocouple is constrained by an ambient environment and also by ageing. As a result, wires in thermocouple measure reduced voltages as the thermoelectric coefficient changes with time. Also, conductors lose homogeneity on prolonged exposure to high temperatures. Different thermocouple varieties are available to suit diverse applications, such as type J, K, T, N etc. Some features of the thermocouple that lender them upper hands are:
- Relatively accurate
- Low cost
- No additional protection required
- Long life
- Sheath protects from corrosive atmosphere
- Lower maintenance costs
One of the disadvantages of using thermocouples is the loss of accuracy when the thermocouple is cycled. For example, when the temperature is varied to a large extent over a period of time, this will cause the thermocouple to “drift”, thus creating errors in the reading.
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