Photoelectric position indicating device

Claim 1

IN A PHOTOELECTRIC POSITION INDICATING DEVICE, A TRANSLUCENT LONGITUDINALLY DISPLACEABLE SCALE BODY PROVIDED WITH OPAQUE LIGHT-REFECTING SCALE MARKS DEFINING A GRADUATED SCALE AND TRANSLUCENT FIELDS BETWEEN SAID SCALE MARKS, MEANS FORMING A LIGHT BEAM FOR ILLUMINATING SAID SCALE BODY FROM ONE SIDE THEREOF, A FIRST PHOTOELECTRIC CELL ON ONE SIDE OF SAID SCALE BODY ADAPTED TO BE ENERGIZED BY LIGHT FROM SAID LIGHT BEAM PASSING THROUGH SAID TRANSLUCENT FIELDS AND A SECOND PHOTOELECTRIC CELL ON THE OTHER SIDE OF SAID SCALE BODY ADAPTED TO BE ENERGIZED BY LIGHT FROM SAID LIGHT BEAM WHICH IS REFLECTED BY ONE OF SAID SCALE MARKS WHEN THE LATTER IS ILLUMINATED BY SAID LIGHT BEAM AND SAID LIGHT BEAM IS BLOCKED BY SAID SCALE MARK FROM PASSING THROUGH SAID SCALE BODY TO ENERGIZE SAID FIRST PHOTOELECTRIC CELL, WHEREBY UPON DISPLACEMENT OF SAID SCALE BODY THE OPAQUE LIGHT-REFLECTING SCALE MARK IS MOVED OUT OF THE PATH OF SAID LIGHT BEAM SO THAT THE LATTER PASSES THROUGH ONE OF SAID TRANSLUCENT FIELDS AND ENERGIZES SAID FIRST PHOTOELECTRIC CELL, WHILE SAID SECOND PHOTOELECTRIC CELL BECOMES DEENERGIZED, A READ-OUT TUBE ARRANGED IN A CIRCUIT WITH SAID TWO ALTERNATELY ENERGIZED PHOTOELECTRIC CELLS, AND MEANS FORMING A SIGNALLING CIRCUIT CONNECTING SAID PHOTOELECTRIC CELLS FOR PRODUCING A VISIBLE SIGNAL WHEN A PREDETERMINED COMPLEMENTARY PATTERN OF LIGHT IMPULSES ENERGIZING SAID PHOTOELECTRIC CELLS IS INTERRUPTED BY IMPURITIES ON SAID SCALE BODY AND BECOMES NON-COMPLEMENTARY.