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Fire detection system

  • US 4,101,872 A
  • Filed: 06/10/1975
  • Issued: 07/18/1978
  • Est. Priority Date: 06/18/1974
  • Status: Expired due to Term
First Claim
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1. A wireless information system transmission system comprising at least two radio frequency signal transmitting means and at least one receiving means associated with the tranmsmitting means, each of the signal transmitting means being arranged to transmit in first and second modes, the first mode being a monitoring mode wherein monitoring mode signals which have a duration δ

  • t and a repetition rate such that said monitoring mode signals are spaced apart by intervals of time t>

    >

    δ

    t are employed to modulate a radio frequency carrier signal,the time interval t between successive monitoring mode signals being allowed to drift randomly between each of the transmitting means,the second mode being an alarm mode, which is established in response to an alarm inducing condition, wherein alarm mode signals having the same duration δ

    t as the monitoring mode signals are employed to modulate the carrier signal, the alarm mode signals having a repetition rate greater than the repetition rate of the monitoring mode signals and being spaced apart by time intervals α

    t,each said monitoring and alarm mode signal associated with the respective transmitting means being composed of a coded pulse train,the receiving means being arranged to receive and detect signals from the transmitting means, the receiving means being arranged to provide an output responsive to a change occurring in the mode of transmission by the transmitting means and to provide an output if no signal having the duration δ

    t is detected within each period of successive predetermined fault detecting periods of time xt >

    t, andthe receiving means being arranged to provide an alarm indicating output if at least one signal of duration δ

    t is received and detected within a receiver alarm detection period of time β

    t, where α

    t≦

    β

    t<

    t, following receipt of a preceding such signal.

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