In the resistance thermometer, the change in resistance of a metal wire due to its change in temperature is the thermometric property. The wire, frequently platinum, may be incorporated in a Wheatstone bridge circuit. The platinum resistance thermometer measures temperature to a high degree of accuracy and sensitivity, which makes it suitable as a standard for the calibration of other thermometers.
In a restricted range, the following quadratic equation is often used :
R = R0 ( 1 + At + Bt2 )
Where,
R0 = Resistance of platinum wire when it is surrounded by melting ice and A and B are constants.