The electronic watt-hour meter (10) comprises an electro-optical watt-hour sensor (12) adapted to be coupled to a consumer's connection to a source of electric power for sensing voltage supplied to, and the current drawn by, the consumer's electric load and for producing output signals indicative of...http://www.google.com/patents/US4489384?utm_source=gb-gplus-sharePatent US4489384 - Electro-optical sensor for watt-hour meter
