Why does an RTD need an excitation source?
Usually an electrical reference or excitation source is required for sensors whose electrical properties are measured. A thermocouple produces a potential difference between the two dissimilar metals that varies with temperature and is repeatable. The measurement is therefore a voltage. The resistance of an RTD changes with temperature, therefore, a constant DC current excitation source is used as a reference to produce a proportionally changing voltage. Thus a signal conditioner which measures an RTD input provides a current reference as excitation and measures the voltage produced.
