Pinhole detectors

Claim 1

IN APPARATUS FOR DETECTING IMPERFECTIONS IN MOVING STRIP BY PHOTOELECTRIC MEANS, (A) A SOURCE OF LIGHT WITHIN A FIRST FREQUENCY RANGE POSITIONED ON ONE SIDE OF SAID STRIP, (B) FIRST LIGHT-SENSITIVE MEANS POSITIONED ON THE OTHER SIDE OF SAID STRIP, (C) SELECTIVE TRANSMISSION MEANS DISPOSED BETWEEN SAID SOURCE AND SAID STRIP FOR CONVERTING TO LIGHT WITHIN A SECOND FREQUENCY RANGE LIGHT WITHIN SAID FIRST FREQUENCY RANGE EMITTED FROM SAID SOURCE TOWARD SAID STRIP IN PLANES NONCOPLANAR WITH PLANES SUBSTANTIALLY PERPENDICULAR TO THE SURFACE OF THE STRIP AND PARALLEL TO THE DIRECTION OF STRIP TRAVEL, (D) A SHUTTER POSITIONED ADJACENT EACH EDGE OF THE STRIP AND ADATPED TO BE DRIVEN TRANSVERSE TO THE DIRECTION OF STRIP TRAVEL, (E) SAID SHUTTER COMPRISING A FIRST SHIELD AND A SECOND SHIELD, (F) SAID FIRST SHIELD EXTENDING INWARDLY OF THE EDGE OF THE STRIP BETWEEN SAID STRIP AND SAID FIRST LIGHT-SENSITIVE MEANS, (G) SAID SECOND SHIELD EXTENDING INWARDLY OF THE EDGE OF THE STRIP BETWEEN SAID STRIP AND SAID SELECTIVE TRANSMISSION MEANS, (H) SAID SHIELDS BEING CHARACTERIZED BY THE PROPERTY OF ABSORBING LIGHT WITHIN SAID FIRST FREQUENCY RANGE, SAID SECOND SHIELD FURTHER BEING CHARACTERIZED BY THE PROPERTY OF TRANSMITTING LIGHT WITHIN SAID SECOND FREQUENCY RANGE, (I) SECOND LIGHT-SENSITIVE MEANS SENSITIVE TO LIGHT WITHIN SAID SECOND FREQUENCY RANGE AND POSITIONED IN SAID FIRST SHIELD TO RECEIVE LIGHT WHICH PASSES AROUND THE EDGE OF THE STRIP, (J) MOTIVE POWER MEANS FOR DRIVING SAID SHUTTER, (K) CONTROL MEANS FOR ENERGIZING SAID MOTIVE POWER MEANS IN RESPONSE TO THE INTENSITY OF LIGHT IMPINGING UPON SAID SECOND LIGHT-SENSITIVE MEANS, AND (L) MEANS DISPOSED BETWEEN SAID STRIP AND SAID FIRST LIGHT-SENSITIVE MEANS FOR TRANSMITTING ONLY LIGHT WITHIN SAID FIRST FREQUENCY RANGE.