Position sensing using an optical potentiometer

A simple optical potentiometer design is proposed for position sensing in large-scale structures during dynamic excitation. The generic optical potentiometer consists of a long thin section of photoluminescent (PL) material terminated by two photodiode detectors. The PL material and photodiode assembly is attached to the moving structure and the material is excited in a light source. The intensity of the light in the PL material decays exponentially with increasing distance from the source. The relative moment between the light source and material is then deduced from the intensity of the light detected by the photodiodes. The preliminary data presented show that this optical potentiometer obeys Beer´s law in a manner similar to the optical fiber system. The expression which describes the variation of intensity at each photodiode versus distance is experimentally determined, together with the attenuation constant. These expressions are solved to produce an equation which calculates the position of the light spot on the tube, given the two photodiode intensities