GUARD ELECTRO-OPTICAL PASSIVE INFRARED ANNUNCIATOR PROVIDED WITH DEVICE FOR DETECTING MASKING OF OBJECT Russian patent published in 2007 - IPC G08B13/191 

FIELD: detection equipment.

SUBSTANCE: annunciator can be used for detection of trespasser within guarded area, for example, for detection in case the trespasser masks the annunciator. Device for detecting tool of masking of annunciator by trespasser is disposed in case of annunciator. The device is made of three light-emitting diodes emitting infrared radiation and of two photodiodes, which receive the radiation. Two light-emitting diodes are taken away the borders of Fresnel lens. One light-emitting diode and both photodiodes are mounted in department of annunciator, which department is closed by Fresnel lens. Longitudinal axis of light-emitting diode belongs to the same vertical plane to coincide with central vertical axis of lens. It forms angle with axis of lens. Photodiodes, disposed at same horizontal line in symmetry with central vertical axis of lens at distance of H from each other and the photodiodes are shifted in relation to light-emitting diode up by distance of h; h relates to H as 1/3.

EFFECT: widened area of detection of masking of Fresnel lens.

4 dwg