The user familiar with the application of industrial thermocouples has certainly already studied and evaluated the relationship of Seebeck thermoelectric effect with the voltages recorded at these terminals. Thermoelectric effects involve the conversion of temperature differences into electrical voltage.
Seebeck effect was discovered in 1821 by the Estonian physicist Thomas Johann Seebeck. The phenomenon indicates that the temperature difference between two electrical conductors or semiconductors from distinct material nature produces a voltage between these two materials.
When heat is applied to one of the two conductors or semiconductors, the electrons became dynamic by the heat. Since only one side of the connection is subjected to heat, the electrons begin to move toward the cooler side of the two conductors. If the two conductors are connected in the form of a circuit, a direct current will flow through the circuit.
Figure 1 - Electrons movement
The voltages derived from the Seebeck effect are reduced. The voltage range produced is usually in the order of microvolts(millionth of volt) by temperature unit.
If the temperature difference is significant enough, some devices may produce a few millivolts. Several devices can be connected in parallel to increase the power supply capacity. These devices have been shown to provide a small-scale level of electrical power if a large temperature difference is maintained between the junctions.
The voltage produced is proportional to the temperature difference between the junctions. The proportionality constant, represented by S, is known as the Seebeck coefficient. Mathematically, the Seebeck coefficient is represented by the following formula:
In the Seebeck coefficient equation, ?V is the voltage difference generated between the two conductive metals and ?T is the temperature difference between the hot and cold sides.
The result of calculating the Seebeck coefficient is directly related to another factor. If the semiconductor material is n-type, the carriers are electrons. In this case the ?V will be positive and in turn the Seebeck coefficient will be negative. If the semiconductor material is of type p, the potential difference will be negative and therefore the Seebeck coefficient will be positive.
The amount of conductive metals is relatively large. These metals have different thermoelectric sensitivities, ie different Seebeck coefficients.
* units in ΔV/ºC. Data registered at 0ºC.
TRANSMITTERS WITH THERMOCOUPLES CONNECTIONS
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