**Explanation:** A Resistance Thermometer or Resistance Temperature Detector is a device which used to determine the temperature by measuring the resistance of pure electrical wire. This wire is referred to as a temperature sensor. If we want to measure temperature with high accuracy, RTD is the only one solution in industries. It has good linear characteristics over a wide range of temperature. The variation of resistance of the metal with the variation of the temperature is given as,

R_{t} = R_{0} [1+(t-t_{0})+beta (t-t_{0})^{2} + .......]

Where, Rt and R0 are the resistance values at toC and t0 oC temperatures. α and β are the constants depends on the metals. In this RTD, the change in resistance value is very small with respect to the temperature. So, the RTD value is measured by using a bridge circuit. By supplying the constant electric current to the bridge circuit and measuring the resulting voltage drop across the resistor, the RTD resistance can be calculated. Thereby, the temperature can be also determined. This temperature is determined by converting the RTD resistance value using a calibration expression.

**Advantages :** Linear over wide operating range Wide temperature operating range High temperature operating range Good stability at high temperature

**Disadvantages: ** Low sensitivity Affected by shock and vibration Requires three or four-wire operation