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Intrusion alarm system for use with two-wire-cable

  • US 4,360,905 A
  • Filed: 04/16/1979
  • Issued: 11/23/1982
  • Est. Priority Date: 04/16/1979
  • Status: Expired due to Term
First Claim
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1. An intrusion alarm system having a plurality of units capable of being interconnected by a cable having only two conductors for detecting the presence of an intruder in a protected area, the system comprising:

  • a plurality of ultrasonic transmitting units;

    a plurality of ultrasonic receiving units;

    a control unit including;

    signal means for applying an ultrasonic frequency AC signal to said two conductors of said cable;

    means for applying DC power to said two conductors; and

    means for detecting an alarm signal applied to said two conductors by one of said receiving units and for producing an alarm indication in response to the detection of an alarm signal;

    means for connecting said plurality of transmitting units to said cable conductors at various locations in said protected area and responsive to the AC signal on said conductors for transmitting an ultrasonic signal into respective locations in the protected area; and

    means for connecting said plurality of receiving units to said cable conductors at said various locations, each said receiving unit including;

    sensor means for receiving echoes of the transmitted ultrasonic signal in its respective area and for producing an output electric signal representative thereof;

    processing means energized by said DC power on said two conductors and responsive to said sensor means output electric signals representative of echoes produced by an intruder for producing an output signal representative thereof; and

    alarm means including an indicator operable to increase the current drawn from said cable for applying said increased current as said alarm signal to said cable conductors in response to said output signal from said processsing means representative of an intruder presence, said increased current producing said alarm indication at said control unit.

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