Definition
A temperature-sensing device made by joining a wire of copper to a wire of constantan (a copper-nickel alloy). When the joined end (the hot junction) is at a different temperature than the other end (the cold or reference junction), a small voltage is produced that is proportional to the temperature difference. This voltage drives a calibrated meter that displays the temperature. Copper-constantan thermocouples are used in aircraft for measuring relatively low temperatures, such as carburetor air temperature.
Plain English
A temperature gauge sensor made by joining two different metal wires -- copper and a copper-nickel mix called constantan. The junction produces a tiny electrical signal that changes with temperature, and that signal is read on a gauge in the cockpit. It is used where the temperatures being measured are not very high.
Context Anchor
Seen in aircraft instrument and maintenance discussions for temperature-measuring systems that use thermocouple wiring.
Derivation
Thermocouple comes from Greek therme (heat) plus couple (a pair joined together) -- literally a heat-sensing pair. Constantan is named for its constant electrical resistance across a wide temperature range, which makes it useful as the second wire in the pair.
Why Pilots Care
Delivers reliable engine temperature data pilots use to avoid overheating and keep the powerplant within safe operating limits.
Grounding Statement
The joined tip senses temperature by turning a heat difference into a very small electrical signal.
Intuition Check
Do not think of this as ordinary copper wire used only to carry electricity. In this term, the copper is one half of a matched metal pair that creates the temperature signal.
Example Sentence 1
The carburetor air temperature gauge is driven by a copper-constantan thermocouple mounted in the carburetor inlet.
Example Sentence 2
During preflight the mechanic verified the copper-constantan thermocouple connections were secure before the next flight.