Patent Number: 044029039
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to control systems which operate with redundant logic channels, and more particularly where these redundant channels are to be physically and electrically independent. Such redundant control systems are employed in nuclear power plants as safety control systems for continued safe operation. It has been the practice to use photoelectric devices to maintain the physical and electrical insulation between the redundant channels, as is taught by U.S. Pat. No. 3,888,772, owned by the assignee of the present invention. Earlier systems interconnected the separate logic channels with either relays or transformers to provide the isolation. Electro-optical devices are well known in which a birefringent crystal is modulated by an applied electric field to vary the light transmission characteristic of the crystal. These devices have been used as electrically controlled switches as described in representative U.S. Pat. Nos. 3,069,973; 3,027,806; and 3,531,179. SUMMARY OF THE INVENTION The present invention utilizes a plurality of electro-optical modulators as coupling means for redundant logic channels while maintaining physical and electrical independence of the logic channels. Fiber optic cable linking means are provided between a system light source and detector, and the plurality of optical logic units which include the electro-optic modulators. Separate operating system sensors are connected to the respective optical logic units and provide operating system condition or parameter indicative signals, which provide the modulation signal for the electro-optic modulators, and to thereby control the light transmission characteristics of these modulators. In the particular embodiment the light intensity passed by the separate electro-optical modulatable member of the separate optical logic units is varied and controlled as a function of the operating system sensor generated signals. These sensors generate signals as a function predetermined system operating condition, and the signal is applied to modulate the light transmissivity through the separate redundant logic channels.