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ALARM-MONITORING SYSTEM

  • US 3,611,361 A
  • Filed: 11/03/1969
  • Issued: 10/05/1971
  • Est. Priority Date: 11/03/1969
  • Status: Expired due to Term
First Claim
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1. A system for individually monitoring at a central station the condition, alarm or nonalarm, of a plurality of alarm condition sensors located at a remote station, said system comprising:

  • first transmitting means at said remote station which are responsive to each of said alarm condition sensors for transmitting to said central station a first sequence of widthmodulated binary signals when none of said alarm condition sensors is in an alarm condition and for transmitting to said central station a complete inversion of said first sequence of width-modulated binary signals when one of said sensors is in an alarm condition, second transmitting means at said remote station which are responsive to each of said sensors for transmitting to said central station a second sequence of width-modulated binary signals when none of said sensors is in an alarm condition, said second signal sequence having at least as many signals as there are sensors to be individually monitored with each sensor associated with a different signal, said second transmitting means operative to transmit an inversion of a sensor-associated signal when said associated sensor is in an alarm condition, means at said central station for interrogating said first and second remote station transmitting means prior to the transmission of each width-modulated signal or inversion thereof of said first and second sequences, first detecting means at said central station for analyzing the signals transmitted by said first transmitting means to determine if said complete inversion of first signal sequence thereof was transmitted, second detecting means at said central station for analyzing the signals transmitted by said second transmitting means to determine if said inversion of a sensor-associated signal was transmitted, and a plurality of alarm indicators each corresponding to a different one of said remote station sensors, and each responsive to both said first and second detectors, each said indicator being activated to alert central station personnel that its respective remote station sensor is in an alarm condition in response to both the detection by said first detecting means of the transmission of a complete inversion of said first signal sequence and the detection by said second detecting means of the transmission of an inversion of its respective sensor-associated signal.

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