Passive infrared intrusion detector and its use

US5942976A · kind A · utility

Assignee

• Cerberus AG · CH

Inventors

• Dieter Wieser · Küsnacht (ZH), CH
• Kurt Muller · Zürich, CH
• Martin Allemann · Wetzikon, CH
• Michael T. Gale · Wettswil, CH
• Thomas Hessler · Lichtenstein, DE

Key dates

• Filing date: Nov 1, 1996
• Grant date: Aug 24, 1999
• Expiry date: Nov 1, 2016

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10S250/01
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A passive infrared intrusion detector for the detection of infrared body radiation includes a sabotage detector, in particular for detecting spraying of the entrance window of the intrusion detector. The sabotage detector includes a light source, a corresponding light sensor, and an optical diffraction grating structure on the outside of the entrance window. The light source and the light sensor can be on the same or on opposite sides of the entrance window. By first- or higher-order diffraction, light from the light source is focused onto the sensor, and a resulting electrical signal from the sensor is evaluated by an evaluation circuit. In case of sabotage, the focusing effect of the optical diffraction grating structure vanishes, so that the light intensity at the detector is reduced. The drop in light intensity triggers a sabotage alarm signal.