Thermocouple

A temperature sensor made from two dissimilar electrical conductors joined together. Its output voltage varies with the temperature difference between the measuring junction and reference junction.

Seebeck effect: The production of voltage in an electrical circuit when its conductors experience a temperature difference. Temperature-dependent voltage at the thermocouple’s junctions is the basis of its signal.
Type K thermocouple: A thermocouple made from chromel and alumel, widely used for general-purpose temperature measurement. Its broad operating range and low cost make it a common practical choice.
Resistance temperature detector: A temperature sensor that infers temperature from the electrical resistance of a metal element. Unlike a thermocouple, it needs an excitation current and measures resistance rather than generated voltage.
Electrical junction: A region where two or more electrical conductors make contact. The measuring and reference junctions are the physical connection points in a thermocouple circuit.
Thomas Johann Seebeck: A German physicist who discovered the thermoelectric effect now called the Seebeck effect. His 1821 experiments revealed the voltage generated in circuits with temperature differences.
Peltier effect: The absorption or release of heat at a junction when electrical current passes between different conductors. It is the related thermoelectric effect that links electrical current and heat flow.
Type J thermocouple: A thermocouple made from iron and copper-nickel alloy, used mainly in moderate-temperature applications. Its iron leg suits some industrial measurements but limits use in oxidizing conditions.
Thermistor: A temperature-sensitive resistor whose resistance changes strongly with temperature. Thermistors are often more sensitive over a narrower range, while thermocouples cover broader ranges.
Reference temperature: A known temperature used as the baseline for interpreting a measurement. Thermocouple voltage depends on the temperature difference from its reference junction.
Leopoldo Nobili: An Italian physicist who developed an early thermoelectric instrument for measuring temperature differences. His thermopile helped turn thermoelectric effects into practical temperature measurement.

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