Importance

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Abstract

A motion detector responsive for infrared radiation, e.g. to use in burglar-alarm installations, comprises an elongate frustopyramidal box with an entrance opening at one end, a concave mirror at the opposite end and four flat, internally reflecting longitudinal walls, two of them converging toward the entrance end on opposite sides of a plane of symmetry with which they include an angle between about 8.degree. and 15.degree.. A pyroelectric radiation sensor near the entrance end, lying in the vicinity of the focal point of the concave mirror, is disposed for illumination by beams of parallel rays in a limited number of fields of view; these beams approach the entrance end at different azimuthal angles, included with the preferably vertical plane of symmetry, but occupy closely adjoining regions inside the box. A planar deflector at the entrance end, bisected by the plane of symmetry, also establishes a limited number of elevational angles for the beams focused upon the radiation sensor.

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First Claim