Optical sensor system and method for monitoring consumables

A method of sensing motion of a sweep hand indicator of a meter which moves adjacent a background surface, the method comprising the steps of:

• illuminating the background surface and the sweep hand indicator by an illumination source defining an illumination field having an axis, the axis of illumination field being positioned at a non-orthogonal angle with respect to the background surface;
• detecting illumination on the background surface by two photo diodes, each defining a field of view having an axis, the axis of field of view of the two photo diodes being positioned substantially in parallel with each other to detect illumination in two separated background surface areas illuminated by the illumination source;
• forming a shadow under the sweep hand indicator upon the sweep hand indicator moving across at least one of said fields of view and upon illumination by the illumination source;
• and
• detecting at least the shadow under the sweep hand indicator by at least one of the two detectors.

A meter reading apparatus to be attached to a utility meter, the apparatus comprising:

• an infrared emitter;
• at least two photo diodes having detection fields being oriented at two separated areas for detecting light in the two separated areas illuminated by the infrared light emitter, wherein the at least two photo diodes are electrically connected in series with each other and with an output node located between the two diodes;
• and
• a comparison circuit having a first comparison input electrically coupled with the output node and a second comparison input electrically coupled with a reference value circuit.

A system for remotely detecting the consumption of a consumable, the apparatus comprising:

• a utility meter having a meter surface and a sweep hand that moves above the meter surface at a rate dependent upon the consumption of a consumable;
• an infrared emitter defining an illumination field having an axis oriented at an angle with respect to the meter surface;
• two photo diodes, each defining a respective detection field having an axis, the detection fields being oriented at two separated areas within the illumination field on the meter surface for detecting infrared illumination in the two separated, wherein the two photo diodes are electrically connected in series with each other and with an output node located between the two diodes;
• and
• a comparison circuit having a first comparison input electrically coupled with the output node and a second comparison input electrically coupled with a reference value circuit.