What is a thermocouple?
A thermocouple consists of two types of wires made of different metals such as copper and iron. The ends of the wires are joined together to form two junctions. The temperature is then calculated using the readings of a voltmeter.
How does a thermocouple thermometer work?
If the two junctions are at different temperatures, a small voltage ( or electromotive force e.m.f) is produced. The greater he difference in temperature, the greater the voltage produced across the ends of the two junctions. if one junction is kept at a fixed temperature, such as 0 degrees celsius, then the other junction can be used as a tiny probe to measure other temperatures.
The defining equation of the thermocouple thermometer is given by :
E= *U
where E= e.m.f produced,
* U is the temperature difference between the reference junction and the probe.
For practical use, especially in measuring high temperatures such as the temperature of lava, the cold junction is removed. This produces a single junction thermocouple. An error of a few degrees in every one thousand degrees may occur but it is often negligible.
The advantages of a thermocouple thermometer are:
1. It is robust, compact, fairly accurate and able to measure a very large temperature range of -200 degrees celsius to 1500 degrees celsius by choosing suitable types of metals for Wire A and B
2. As the wires junctions are very small, the thermometer can be used to measure temperatures at a point
3. It is very responsive to rapidly changing temperature due to its small mass and because metals are good conductors of heat.
4. As the output is an electrical signal, it can be connected to suitable electrical equipment for checking rapid or sudden temperature changes.
