Infra-sonic detector and alarm with self adjusting reference
US4890265A · kind A · utility
5Cited by
3References
5Claims
0Family size
Assignee
Inventor
Key dates
| Filing date | Aug 3, 1988 |
| Grant date | Dec 26, 1989 |
| Priority date | — |
| Expiry date | Aug 3, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/1681
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
A detector and alarm is provided for monitoring air pressure variations in a monitored space, which variations correspond to an intrusion. An infra-sonic detector includes a microphone or the like and a low pass filter to retain only low frequency infra-sonic signals. The instantaneous infra-sonic signals are compared against a variable reference signal, which is a voltage lagging or delayed variant of the instantaneous signals. In this manner the detector is self adjusting for slow variations in the instantaneous signals but responds immediately to rapid variations to trigger an alarm.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.