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Multiple sensor intrusion alarm system

  • US 4,206,449 A
  • Filed: 07/27/1977
  • Issued: 06/03/1980
  • Est. Priority Date: 07/27/1977
  • Status: Expired due to Term
First Claim
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1. An intrusion alarm system, comprising:

  • a plurality of sensors for detecting the occurrence of an event and for producing an alarm signal indicative thereof;

    a sensor coordinator;

    a two-conductor cable interconnecting each of the plurality of sensors with the sensor coordinator;

    the sensor coordinator including;

    digital processor means; and

    modulator-demodulator means connected between said processor means and said cable, for transmitting signals from said processor means along said cable, and for receiving status signals returned by said sensors and providing digital signals representative thereof to said processor means;

    the processor means periodically transmitting a synchronizing pulse and monitoring said cable thereafter to sense the presence of status pulses and to determine the width of said sensed pulses;

    a like plurality of interface means, each of said interface means being connected in parallel to said cable and each associated with a respective one of said sensors, for responding to said synchronizing pulse by returning back along said cable to said sensor coordinator said status signal representative of the presence or absence of an alarm signal from the associated sensor;

    each of said interface means including;

    delay means for determining a delay time and for causing the status signal to be returned by said interface means after the elapse of the delay time following the transmission of the synchronizing pulse by said sensor coordinator;

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