# Resistance Temperature Detector (RTD): Construction, Working Principle, Types and Advantages

We know that the resistance of metallic conductors increases with temperature. Thermal sensors using this property of metallic conductors are called Resistance Temperature Detector(RTD).

## Construction of RTD

The resistance temperature detector is constructed by wounding the resistance wire on a mica base. The wire is wound like a helical coil on the support to reduce the inductance effect. The terminals(Leads) are brought out of the pipe. The coil is protected by a stainless steel case. The structural view of a wire wound RTD is shown in the figure.

Copper, Nickel and Platinum are the most used RTD materials. These metals have positive temperature co-efficient and possess poor thermal sensitivity. Also, the resistance-temperature characteristics of these materials are approximately linear.

Another type of RTD is thin-film RTD that is constructed by depositing a thin layer of resistive material onto a ceramic substance.

## Working Principle of RTD

Resistance Temperature Detectors (RTD) operates on the principle that the resistance of a metal changes with changes in temperature.

The variation of resistance R with temperature t can be represented by the equation,

$$R_t=R_0(1+\alpha \: \Delta t)$$

Where α is the temperature co-efficient at t0 and R0 is the resistance at t0.