Experimenting with Thermocouples.

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Physics AS Level Coursework

Experimenting with Thermocouples

Introduction

For my sensor coursework, I have chosen to investigate the properties of thermocouples. A thermocouple is a sensor which detects a temperature difference, and produces a very small electrical output.

"In 1822, an Estonian physician named Thomas Seebeck discovered (accidentally) that the junction between two metals generates a voltage which is a function of temperature. Thermocouples rely on this Seebeck effect. Although almost any two types of metal can be used to make a thermocouple, a number of standard types are used because they possess predictable output voltages and large temperature gradients."

Source: http://www.picotech.com/applications/thermocouple.html

Welding, or otherwise combining, two dissimilar metals can make a thermocouple. Varying the temperature of the junction where the two metals combine will produce a very small voltage and a very small current.

However, if one attempts to connect the thermocouple to a Voltmeter, another thermocouple junction is made. This is at the point of contact, where the ends of the thermocouples meet the contacts of the Voltmeter, and causes problems, as it can lead to errors in the result. To compensate for this, a technique known as cold junction