Cable extension linear position sensors are used to measure the movement and displacement of objects. A cable is attached to the movable object, and, as the object moves, the transducer produces an electrical signal proportional to the cable's linear extension. Typically cable extension transducers contain a cylindrical spool that turns as the cable reels and unreels. The spool is coupled to the shaft of a rotational sensor. As the transducer's cable extends along with the movable object, it causes the spool and sensor shafts to rotate. The rotating shaft creates an electrical signal proportional to the cable's linear extension. Velocity output is available on some models as well.