Thermocouple
A temperature sensor that produces a tiny voltage proportional to the temperature at its junction.
What it is
A thermocouple is a temperature sensor made from two different metals joined at a junction. Heat the junction and it produces a small, predictable voltage that a controller reads as a temperature.
How it works
The junction of two dissimilar metals generates a tiny voltage that varies with temperature. Different metal combinations form different 'types', each with its own range and the matching extension wire it must be connected with.
Thermocouples are polarity-sensitive — reverse the leads and the reading moves the wrong way. The controller must be set to the correct type, or the temperature will read wrong.
Where it's used
Ovens, furnaces, plastics, and process heating where accurate, wide-range temperature measurement is needed. An open thermocouple gives a sensor-break; the wrong type or reversed polarity gives a wrong reading.
Related faults
Thermocouple open or reversed (wrong temperature reading)
A thermocouple gives a wrong temperature — reads way off, shows an open/sensor-break, or moves the wrong way — so the heat control can't work properly.
Heater overshooting or oscillating around setpoint
The process temperature overshoots the setpoint then cycles above and below it, instead of settling — poor control that can spoil product or trip high-limits.
Electric oven not heating
The oven powers up (light/clock may work) but doesn't get hot — pointing at the element, thermostat, or the oven's controls rather than the supply.
Related definitions
Thermostat
Switches a heating or cooling load on and off to hold a temperature at a setpoint.
Heating element
A resistive conductor that turns electrical energy into heat — the business end of most electric heating.
SSR (Solid-State Relay)
Switches a load electronically with no moving parts — fast, silent, ideal for frequent switching like heaters.