A method and an apparatus for detecting opaque members are within a detection space.

摘要

A method and apparatus for detecting opaque members when within detection space. The method includes the steps of sequentially effecting a radiant energy transmission across a detection space (3) from a plurality of spaced apart sources (1) and causing a detection signal when such transmission is not sufficiently detected at each of a plurality of receivers (2) at sequentially correspondingly selected locations. The apparatus includes a plurality of radiant energy transmitting devices (1), a corresponding plurality of radiant energy receivers (2) and associated electronic control means, the transmitting means being activated in a predetermined sequence during finite time periods. There are also means provided to detect, between the finite time periods, any stray sources of radiant energy. The apparatus can be interfaced with power machinery to provide a safety mechanism therefor, or be used in an intrusion alarm system.