Abstract: A sensor of the linear voltage differential transformer (LVDT) type is described, with a moveable core, which has both high permeability and magnetic retentivity, to thereby provide both position and velocity signals. Also described are various embodiments of a position sensor which provides a position signal of the same amplitude, example a null, whenever the sensor's core is at any one of controllable selected positions within the sensor. Any of these sensors may include a core with magnetic retentivity to provide a velocity signal. A servo control system is disclosed, utilizing the position signals from one of the sensors, as described, to control the positioning of an element at either of two positions.