Photo variable potentiometer with photoresistive surface - is without positionally variable electrical contact and uses fibre or prismatic light guides

摘要

The potentiometer has its resistance varied by a light beam falling on a photo - resistive surface. The potentiometer has therefore no adjustable electrical connection on the resistive surface. The photo - resistive track (2) may be in the form of a flat disc or a strip bent into a shallow cylinder. In both cases the light source in the form of a bulb (27) is positioned at one end of a rod (22) running through the axis of the assembly. The light beam is deflected from the axis either by a fibre - optic bundle (29) or by a prismic light guide. Variation in resistance is by rotation of the central rod and hence movement of a trapezoidal light spot over the resistive surface.