Infra-sonic detector and alarm with self adjusting reference
US4991145A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 2, 1989 |
| Grant date | Feb 5, 1991 |
| Priority date | — |
| Expiry date | Jun 2, 2009 |
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 or a bandpass filter to retain a particular range of frequencies between approximately 5 Hz and 12 Hz. 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. In one embodiment the detector only senses negative going air pressure changes to trigger an alarm in order to minimize the incidence of false alarms.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.