When a voltage is applied to a metal, at the ends electrons will start moving to the positive pole.
This movement of electrons is interfered with by imperfections in the metals crystal structure which is non temperature-dependent. This phenomenon creates a constant resistance. While the temperature rises, the vibrations of the metal atoms on their roster increases. This restricts the movement of the conducting electrons. The vibrations increase linearly with temperature which results in the increase of resistance. The increase in resistance is directly proportional to the temperature. This effect is referred to as the positive temperature coefficient.
The ideal temperature measurement would have a high temperature coefficient which would result in de biggest change in resistance with temperature. Also the ideal temperature measurement would not change in characteristic properties over a long period of time. The ideal measurement can also not be influenced by chemical effects.
The relationship between resistance and temperature is relatively linear, resulting in Pt100 sensors to be extremely accurate for a certain set temperature. Due to its linearity, Pt sensors are very stable. Furthermore, RTD sensors have high repeatability.
Usually, Pt sensors are preferred over thermocouples when the high precision measurement is required in a temperature range up to 600°C.
In general, it is impossible to conclude whether RTDs or thermocouples are better. Instead, it is more useful to compare the performance of RTDs and thermocouples by addressing other factors, such as measuring range, accuracy, costs, and response time.
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