Three Wire RTD
The three wires RTD is the most popular configuration for use in industrial applications. In order to minimize the effects of the lead resistances, a three-wire configuration can be used.
Using this method the two leads to the sensor are on adjoining arms. There is a lead resistance in each arm of the bridge so that the resistance is cancelled out, so long as the two lead resistances are accurately the same. This configuration allows up to 600 meters of cable.
When used correctly, the three wire configuration eliminates the series resistance. This permits an accurate measurement of the sensing element.
Two of the leads are connected to one side of the sensing element and the single lead to the other side. The resistance in L1 and L3 should be matched as close as possible; this will cause the lead resistance to cancel them. The color code for a three wire RTD is two red wires and one white.