Resistance Temperature Devices (RTD)

Resistive temperature devices work on the principle that the electrical resistance of a material changes with its temperature. There are two key types of the devices: RTD and thermistors. It is well known that resistance of metallic conductors increases with temperature, while that of semiconductors generally decreases with temperature. Resistance thermometers employing metallic conductors for temperature measurement are called Resistance Temperature Detector (RTD), and those employing semiconductors are termed as thermistors. As their name indicates, RTDs rely on resistance change in a metal, with the resistance rising more or less linearly with temperature. Thermistors are based on resistance change in a ceramic semiconductor; the resistance drops non-linearly with temperature rise. The variation of resistance of metals with temperature is normally modelled in the form:

R₁ = R₀ [1 + α (t − t₀)]

where R₀ and R₁ are resistance at temperature t and t₀, respectively.