Measurement of temperature with a resistance temperature detector is a matter of measuring resistance. Unbalanced Wheatstone bridge method are invariably used to measure the resistance.
The majority of RTD sensor applications standardize on three Or four leadwire systems. The difference between the two construction is accuracy.
An RTD sensing element like any other thermometer, senses its own temperature, accuracy depends on the ability of the RTD to conduct heat from its outer sheath to the element wire.