Portable electronic alarm device
US4314239A · kind A · utility
Inventors
Key dates
| Filing date | Dec 13, 1979 |
| Grant date | Feb 2, 1982 |
| Priority date | — |
| Expiry date | Dec 13, 1999 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B19/005
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
To detect an intrusion the apparatus projects one or, better, two beams of infrared rays in a direction selected by the user. A lens collects part of the radiation diffused back by the surface on which the beam impinges (whose distance must be in the range covered by the apparatus) and concentrates the collected radiation to form an image, almost pin point, of the "illuminated" surface. The position of said image depends on the distance of the surface impinged on by the beam. A photodetector provided with a slit placed in front is displaced until it detects the radiation forming the image. When the intruder intercepts the beam, the image of the "illuminated" surface, which is now on the intruder, will shift sideways enough to prevent the rays from passing through the slit and therefore from reaching the photodetector. The absence of the photodetector output signal indicates that an intrusion is occuring. The apparatus may be enabled to perform as fire detector, by means of a second photodetector fixed beside the former and before the diaphragm.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.