System for detecting a movable entity within a selected space

Details System for detecting a movable entity within a selected space System for detecting a movable entity within a selected space

1993-01-25

1995-04-11

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

454 56, G01V 904

Patent

active

054060737

ABSTRACT:
A system is provided for detecting presence and/or motion of a person or other movable entity within a selected space. Detection is accomplished by detecting reflected light or other radiation from the space, presence being signified when detected radiation differs from an established background, either up or down, by an amount exceeding a predetermined threshold. Blending of the entity with the background is avoided by viewing the entity at at least two different angles with different background, for example by use of two spaced detectors, and variations in background are automatically compensated for when a presence indication persists for a selected period of time after the last motion indication is received. The background is updated to the current level when this occurs. With light radiation, the light sources are structured to irradiate substantially the entire space and saturation of a detector by ambient radiation is avoided by providing a bandpass filter which passes only radiation in a narrow overlap wavelength band for the radiation sources and detectors.

REFERENCES:
patent: 4967083 (1990-10-01), Kornbrekkle et al.
patent: 5196689 (1993-03-01), Sugita et al.
patent: 5225689 (1993-07-01), Buckle et al.
patent: 5240455 (1993-08-01), Sharp
patent: 5245117 (1993-09-01), Schiller

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