Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1979-11-05
1981-09-15
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
367901, G08B 1322
Patent
active
042900581
ABSTRACT:
The oscillations which are generated during an attempted instrusion at a protected area or surface, for instance a vault wall or fence, are received at a sonic receiver and processed by an evaluation circuit such that only the oscillations emanating from an intrusion attempt trip an alarm, not however spurious oscillations from the surroundings. The received oscillations are mixed with a carrier frequency whose frequency periodically and continuously passes through a certain frequency range. The mixed signals are filtered in a narrow band frequency range, so that at the output, during each frequency through pass period, there appears the entire frequency spectrum of the received sonic oscillations in the evaluated frequency range. The filtered signals are integrated and the integrated signal, after a brief period of time, is reset as a frequency throughpass if no further signal appears. This integrated signal reaches an alarm threshold only upon occurrence of irregular oscillations in the evaluated frequency band, not however in the presence of disturbances due to individual periodic oscillations or spurious oscillations outside of the frequency range.
REFERENCES:
patent: 3134970 (1964-05-01), Kelly et al.
patent: 3147467 (1964-09-01), Laakmann
patent: 3471846 (1969-10-01), Cotter et al.
patent: 4099168 (1978-07-01), Kedjierski et al.
Cerberus AG
Kleeman Werner W.
Swann III Glen R.
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