Passive intrusion detection system
US4197530A · kind A · utility
Inventors
Key dates
| Filing date | Feb 9, 1977 |
| Grant date | Apr 8, 1980 |
| Priority date | — |
| Expiry date | Feb 9, 1997 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/26
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
An intrusion detection system in which crystal oscillators are used to provide a frequency which varies as a function of fluctuations of a particular environmental property of the atmosphere, e.g., humidity, in the protected volume. The system is based on the discovery that the frequency of an oscillator whose crystal is humidity sensitive, varies at a frequency or rate which is within a known frequency band, due to the entry of an intruder into the protected volume. The variable frequency is converted into a voltage which is then filtered by a filtering arrangement which permits only voltage variations at frequencies within the known frequency band to activate an alarm while inhibiting the alarm activation when the voltage frequency is below or above the known frequency band.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.