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Multi-sensor alarm system and method of protecting a premises

  • US 4,361,833 A
  • Filed: 03/25/1980
  • Issued: 11/30/1982
  • Est. Priority Date: 03/25/1980
  • Status: Expired due to Term
First Claim
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1. A multi-sensor alarm system, comprising:

  • (a) electrical circuit means for establishing a two-wire closed loop circuit path having a load impedance through which an electrical current is conducted;

    (b) first sensor means electrically connected in the two-wire closed loop circuit path for detecting an alarm event, said first sensor means being actuatable in response to detection of the alarm event from a non-alarm state in which the electrical current is conducted through the first sensor means, to an alarm state in which the electrical current is prevented from being conducted through the first sensor means;

    (c) second sensor means electrically connected in the same two-wire closed loop circuit path for detecting the alarm event, said second sensor means being actuatable in response to detection of the alarm event from a non-alarm state in which the electrical current is prevented from being conducted through the second sensor means, to an alarm state in which the electrical current is conducted through the second sensor means;

    (d) each of said sensor means being respectively operative to differently change the electrical characteristics of the two-wire closed loop circuit path in response to actuation of each sensor means between its respective states;

    (e) alarm means electrically connected to the same two-wire closed loop circuit path, for sensing either differently changed electrical characteristic of the circuit path, and for generating an alarm signal when either of the sensor means is in its respective alarm state, said alarm means including a switching element actuatable among a fully-on switched condition, a fully-off switched condition, and an equilibrium condition intermediate the fully-on and fully-off switched conditions, and means for establishing the equilibrium condition when both sensor means are in their non-alarm states, and wherein each of said sensor means is operative to actuate the switching element away from its equilibrium condition when either sensor means is in its respective alarm state; and

    (f) supervisory means for constantly monitoring the status of the switching element and the sensor means, said supervisory means being operative to separately indicate when both sensor means are in their non-alarm states and said switching element is in its equilibrium condition, and to separately indicate when said first sensor means is in its respective alarm state and said switching element is in one of said switched conditions, and to separately indicate when said second sensor means is in its respective alarm state and said switching element is in the other of said switched conditions.

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