Data Instruments, Inc.

Raymond C Webb

Daniel R Weber

The invention is an improvement over the system disclosed in U.S. Pat. No. 3,805,061 for detecting intrusion of a selected area by an object and for operating or terminating operation of an associated apparatus when such intrusion occurs. It consists of improved transmitter and receiver units. The transmitter comprises a plurality of radiant energy sources that are strobed sequentially and repetitively by a clocked counter. The receiver has a plurality of radiant energy detectors, means for enabling the detectors sequentially and in synchronism with the strobing of the radiant energy sources, dual control relay means for operating or terminating operation of an associated apparatus, and cross coupled control circuits for causing the relay means to change states if a radiant energy detector fails to detect a radiant energy beam while it is enabled. The receiver's control circuits include pulse detection means for determining if the radiant energy detectors produce pulses in response to incident radiant energy beams, and means for accomplishing at least one of the following: (a) deactivating the relay means if a relay driver has a fault, (b) deactivating the relay means if a pair of relay contacts are stuck closed, (c) terminating flow of current to some or all of the solid state components such as counters, switches, etc. of the receiver when a fault occurs in a relay control circuit, and (d) providing visual indications of the state of the relays.

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Foxboro, MA, United States of America

Raymond C Webb