Position sensing system with magnetic coupling

The position of an aircraft control surface actuator is determined by a combination of a linear transducer and light radar. A link has a first end attached to a magnet and a second end attached to the actuator. Movement of the actuator causes the magnet to move axially along the outer cylindrical surface of a hermetically sealed housing. The transducer includes a magnetic coupling between the magnet end and a ferromagnetic follower inside the sealed housing. Preferably, the magnet is a ring magnet, and the ferromagnetic follower is a tubular cylinder. The follower carries a corner cube reflector that receives light from, and reflects light back to, the end of an optical fiber. The transit time of the light is measured and is used to calculate the distance between the fiber end and the reflector to thereby determine the position of the actuator. The hollow configuration of the follower increases magnetic flux exiting from the flat end surfaces of the follower to increase the strength of the magnetic coupling and also reduces the mass of the follower to reduce the displacement inaccuracy during acceleration. The length of the follower is preferably equal to the distance between the poles of the magnet.