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# Thermocouples

Thermocouples are electrical temperature sensors which are capable of converting heat into voltage.

In this lesson we will examine the principle behind how thermocouples work.

And we will look at a common complication with thermocouples and how we overcome it.

# How it Works

A thermocouple consists of two wires, each made of a different metal or metal alloy.

The metals are welded together at one end to form a measuring junction. (Or, as some people prefer to call it, the hot junction.)

Wait, let's back up a second.

When one end of a metal wire is heated up, electrons in the heated end gain energy and begin to drift toward the cooler end until they reach an energy equilibrium again.

This equilibrium point for any given temperature is different for different metals.

Now, if we were to measure the voltage across one end to the other of a single heated wire we would see that a voltage drop has been induced.

But we cannot actually measure this voltage drop because one end of the wire is placed somewhere very hot!

This is where the second wire comes in.

Instead of trying to measure the voltage drop across a wire we can measure the voltage at the cold end of the two different wires.

Since the different metals have different voltages induced by their drifting electrons, when we compare them we will measure a voltage differential.

The amount of voltage produced is very small.
We're talking in the millivolt range.

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