A fully redundant safety interlock system is provided comprising, means for detecting the loss of light on a fiber optic link; controller means, coupled to said means for detecting, for determining the safety condition of the link based on the output of said means for detecting, and for controlling the...http://www.google.es/patents/US5136410?utm_source=gb-gplus-sharePatente US5136410 - Optical fiber link control safety system
