• Preface
• Table of Contents
• Index
• References
• Media Response
• Ferrites
• Piezoelectric ceramics
• Piezoelectric crystals
• Transformers
• Sensors, Transducers, ...

Thermocouples
The operation of the thermocouples is based on the Seedbeck phenomenon. According to this, when two different metals or alloys contact each other, then, due to their different output work, free electrons are moving from the metal with the smallest output work to the metal with the biggest output work, even if no exterior voltage is applied to them. Thus, the first metal is becoming more positive than the other, causing a ‘contact voltage’ on the point of contact. If the two free ends have different temperature, an electromagnetic force is developed, which is equal to:
where a, b, c are constants dependent on the materials involving and ΔT is the temperature difference between the metals. Because the constant c is very small, if the cold contact is in 0°C, then the equation 10.14 is:


where T is the temperature of the hot contact and a and b are constants dependent on the contact type. We also define the neutral temperature TN as that in which the electromagnetic force is maximized and this is:It is used to determine the measurements area of temperature for a specific contact type. In practical terms, we don’t use a single contact but two contacts, a cold one and a hot one, as shown in Figure.