Abstract: An optical encoder for use with a liquid level measuring device including a pre-encoded film strip bidirectionally translatable between a pair of film reels past a detection station. The film is driven by a sprocket coupled to the spring motor of a perforated tape level gauge, and motion translating means enable the film to be unwound smoothly in either direction. The film has a plurality of digitally encoded tracks which enable an optical detection station to provide information specifying the level of the liquid.The motion translating means includes first and second hub members rotatably secured to a support member for rotation about the axis of a different one of the film reels, each hub member being provided with a gear portion for mutual driving engagement.The tension maintaining means includes first and second spring members each coupled between a film reel and a hub member, and received in a central recess of the associated hub member.

Abstract: An optical encoder unit for generating digital electrical signals defining the absolute level of a liquid in a tank from the translational position of a perforated tape in a conventional liquid level gauge and providing both local and remote readout. A pre-encoded film strip has a plurality of laterally spaced longitudinally extending tracks with transparent and opaque regions encoded in Gray code format, is received on a pair of freely rotatable spools, and is guided past an optical detection station by a pair of spaced stationary guide members. A rotatable sprocket having an input shaft adapted to be driven by a shaft coupled to a sprocket in a conventional perforated tape liquid level gauge drives the film strip past the detection station in response to movement of the tape. A spring biased pivotally mounted tension arm having a guide in surface contact with the film strip maintains tension therein as the film strip is moved from reel to reel.