Infra-sonic detector and alarm with self adjusting reference

Details Infra-sonic detector and alarm with self adjusting reference Infra-sonic detector and alarm with self adjusting reference

1989-06-02

1991-02-05

Eisenzopf, Reinhard J.

Communications, electrical: acoustic wave systems and devices

Echo systems

Presence or movement only detection

200 6162, 307116, 307141, 340566, G08B 1322

Patent

active

049911457

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.

REFERENCES:
patent: 4468763 (1984-08-01), Braunling et al.
patent: 4586031 (1986-04-01), Grinneiser
patent: 4800298 (1989-01-01), Miller
patent: 4890265 (1989-12-01), Goldstein

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