Method and apparatus for intrusion detection by using sonic receivers
First Claim
1. A method for detecting an intrusion, comprising the steps of:
- obtaining signals delivered by a sonic receiver mounted at the object to be protected;
mixing the obtained signals with a carrier frequency whose frequency periodically and continuously passes within a given time duration through a predetermined frequency range;
filtering the mixed signal in a narrow band frequency range;
upon occurrence of a filtered signal activating a timing circuit having a predetermined time duration;
integrating the filtered signal;
resetting the result of the integrated filtered signal whenever the filtered signals are interrupted for at least said time duration of the timing circuit;
said time duration at most being equal to the time duration of a frequency throughpass; and
triggering an alarm signal as soon as the integrated signal reaches a predetermined threshold within the reset time.
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Accused Products
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.
11 Citations
14 Claims
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1. A method for detecting an intrusion, comprising the steps of:
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obtaining signals delivered by a sonic receiver mounted at the object to be protected; mixing the obtained signals with a carrier frequency whose frequency periodically and continuously passes within a given time duration through a predetermined frequency range; filtering the mixed signal in a narrow band frequency range; upon occurrence of a filtered signal activating a timing circuit having a predetermined time duration; integrating the filtered signal; resetting the result of the integrated filtered signal whenever the filtered signals are interrupted for at least said time duration of the timing circuit; said time duration at most being equal to the time duration of a frequency throughpass; and triggering an alarm signal as soon as the integrated signal reaches a predetermined threshold within the reset time. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for intrusion detection comprising:
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sonic receiver means mounted at an object to be protected and receiving sonic oscillations; an electronic evaluation circuit connected with said sonic receiver means; said electronic evaluation circuit delivering signals when the received sonic oscillations exceed predetermined values; said electronic evaluation circuit; a mixing stage which mixes the signals delivered by the sonic receiver means with a carrier frequency which is periodically and continuously swept through a predetermined frequency range within a predetermined period; circuit means having a frequency throughpass in a narrow band frequency range for processing the mixed signals; said circuit means having an output at which there appears the frequency spectrum of the signals in the carrier frequency sweep range which are delivered by the sonic receiver means; an integrator for integration of the output signals of the narrow band circuit means; a reset circuit for the integrator having a reset time which at most is equal to the carrier frequency sweep period; and a threshold value switch for triggering an alarm as soon as the integrator output signal exceeds, within the reset time, a predetermined value. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification