This invention relates to safety apparatus intended for use in conjunction with industrial machinery especially of a type such as presses and guillotines. The invention employs a radiant energy safety screen with the ability to detect the presence of extraneous radiation or a failure of radiant energy...http://www.google.fr/patents/US4520262?utm_source=gb-gplus-shareBrevet US4520262 - Photoelectric safety screen with stray source detection
Photoelectric safety screen with stray source detection
