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What Do Thermocouples Measure?

Did you know that thermocouples don’t actually measure temperature?

They actually measure a very small electric current generated by the junction of two dissimilar metals being subjected to heat.

How small is the current?

It is only a few millivolts (thousandths of a volt) and that millivolt signal is converted to a temperature value by instrumentation. The signal from a thermocouple at 1150°F is around 25.8 millivolts or 0.0258 volts.  Compare that to the voltage from a car battery, or an AA battery.

(The term “T/C” is the abbreviation for Thermocouple)

Why does this matter?

Specially selected metals are paired to make thermocouples, and each pair is designated by “Type”. Each Type generates a different voltage at same temperature, so it is very important to always use the right Type of thermocouple (T/C) on equipment. If a Type K thermocouple was used on an oven with a controller set for Type J, at a setpoint of 1000°F, the oven could heat to over 1300°F.

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