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Seismic intrusion detector system

  • US 3,984,803 A
  • Filed: 09/06/1967
  • Issued: 10/05/1976
  • Est. Priority Date: 09/06/1967
  • Status: Expired due to Term
First Claim
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1. A surveillance system for monitoring man-associated seismic movements within a control area, comprising:

  • means for generating an electrical signal responsive to seismic movement of the generating means;

    a bandpass amplifier coupled to said generating means and having a bandpass between about 10 and 40 Hz to permit electrical signals representative of man-associated movements to pass;

    threshold detector means for sensing signals from said bandpass amplifier exceeding a preselected voltage level greater than signals generated within said area by normal background noise within the bandpass range and for generating a pulse coicident with the first cycle of the seismic signal each time said voltage level is exceeded;

    inhibitor circuit means for generating pulses responsive to said detector means output pulses separated by more than a given time period;

    precounter means responsive to said trigger pulses for generating a resultant pulse when a preselected number of trigger pulses have been counted representing each man-associated intrusion into said control area;

    counter means for counting said resultant pulses and for generating a volage proportional to the total count in said counter means;

    normally disabled variable frequency oscillator means for generating an audio frequency signal proportional to the amplitude of said counter voltage;

    means for enabling said oscillator means and for monitoring the resulting audio frequency signal to determine the number of man-associated seismic movements within said area.

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