What's the Difference? 2-wire, 3-wire, 4-wire RTDs

The measuring circuit is a Wheatstone Bridge variant. The resistance element forms one of the four resistances in the bridge. The 3-wire RTD allows the lead resistances to be removed from the variables and a more accurate temperature measurement to be made, compared to the 2-wire. Lead resistance may be significant in the case of a system with long cable runs between the sensor and the transmitter.

Perhaps another reader can expand on the 4-wire RTD?

The 4-wire version works on the same principle as a DC power supply with remote voltage sensing/feedback.

It's just another way of eliminating errors due to lead resistance. The signal leads carry no excitation current, so the lead resistance cannot affect the temperature measurement.

A 2 wire RTD simply puts both leads in the same leg of a Wheatstone Bridge.Variations in temperature of the path of the leads can lead to errors. A 3 wire RTD places the 3rd lead in the opposite side of the Bridge,thus compensating for lead resistance. A 4 wire RTD places the 4th lead in the diagonally opposite lead from the element.This further reduces errors due to temperature changes along the length of long leads. The output of the bridge is measured diagonally using an op-amp.The signal from the amplifier is passed on to conditioning and scaler circuitry, and then to an A/D converter.The type of converter depends on required speed and accuracy, whether it is single,dual slope, successive approximation,flash, etc. Hope this info is helpful. HTRN

please answer this with examples.

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