Definition
A temperature-sensing device made of two dissimilar metal wires joined at one end. When that junction is heated, a small voltage is produced that is proportional to the temperature difference between the heated junction and the cooler reference end. The voltage is read by a gauge calibrated to display temperature.
Plain English
A heat sensor made by joining two different metals. The hotter the joint gets, the more electricity it produces, and a gauge converts that electricity into a temperature reading.
Context Anchor
Seen in aircraft temperature indicating systems, especially probes and wiring for high-temperature engine or exhaust readings.
Derivation
From 'thermo' (Greek 'therme', meaning heat) and 'couple' (from Latin 'copula', meaning a joining or pair). Literally a 'heat pair' — two metals paired together to sense heat. The name describes exactly how it works.
Why Pilots Care
Allows pilots to monitor engine temperatures in real time to prevent overheating and detect issues like leaning problems or cooling failures.
Analogy
Like a tiny battery that gets stronger the hotter one end gets compared to the other.
Grounding Statement
When the hot end of the thermocouple is heated, the joined metals create a small signal that the instrument converts into a temperature reading.
Intuition Check
A thermocouple is not two thermometers connected together. It is a joined pair of different metals that creates an electrical signal when its temperature changes.
Example Sentence 1
The cylinder head temperature gauge is driven by a thermocouple bolted to the hottest cylinder.
Example Sentence 2
A faulty thermocouple can give inaccurate cylinder head temperature readings during flight.