Bucause the RTD is a resistive device, we need to pass a current through it and monitor the resulting voltage. However, any variation in resistance due to self heat of resistive wires as the current flows through it, 12R, (ohms Law) causes an error in the readings. To avoid this, RTD,s are generally connected into Wheatstone Bridge networks and have additional connecting wires for lead compensation and/or connection to constant current sources.