Model Temperature Measurement

Thermocouples are deceptively simple devices which are used to measure temperature.

In wind tunnel testing, they are most often used to measure air temperature within ducts inside a model – for example in an intake test where there may be a need to measure the temperature of the air approaching the engine inlet face.

A thermocouple is simply a junction between two wires made from different metals.

How Thermocouples Work

In 1821, a scientist called Thomas Seebeck discovered that when two wires of dissimilar metals are joined at both ends and one of the ends is heated, a continuous electrical current is produced in the loop created by the two wires.

This remarkable and very useful property is due to the fact that electrons are more strongly attracted to some metals than others, and this difference in attractive force grows with an increase in temperature. Even room temperature is sufficient for electrons to move from one metal to another.

In the diagram above, electrons are more strongly attracted to metal “B” at the hot junction between the two wires than at the cold junction and so electrons are pumped around the wire loop generating an electric current; this current can be measured and from this measurement the temperature at the hot junction of the wire loop can be calculated.