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Method of, and circuit arrangement for, function control of ultrasonic alarm installations

  • US 4,729,120 A
  • Filed: 09/23/1985
  • Issued: 03/01/1988
  • Est. Priority Date: 02/13/1984
  • Status: Expired due to Fees
First Claim
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1. A method of testing an ultrasonic alarm installation, comprising the steps of:

  • generating ultrasonic waves of a predetermined frequency using an ultrasonic transmitter;

    emitting said ultrasonic waves generated by said ultrasonic transmitter, into a predetermined region to be monitored;

    receiving ultrasonic waves originating from said monitored region by means of an ultrasonic receiver and thereby converting said received ultrasonic waves into an electrical signal;

    feeding said electrical signal to an electrical evaluation circuit;

    processing said electrical signal and triggering by means of said electrical evaluation circuit, an alarm signal upon a predetermined frequency deviation of said received ultrasonic waves from said emitted ultrasonic waves;

    producing said predetermined frequency deviation during a test phase of the operation of the ultrasonic alarm installation;

    said step of producing said predetermined frequency deviation during said test phase entailing the steps of;

    producing a predetermined frequency spectrum includng said predetermined frequency deviation effective for triggering said alarm signal, using a modulation frequency generator;

    modulating said frequency of said ultrasonic waves emitted by said ultrasonic transmitter by said predetermined frequency spectrum including said frequency deviation effective for triggering said alarm signal;

    generating a reference signal using a reference signal generator;

    switching off at least said modulation frequency generator; and

    after switching off said modulation frequency generator, evaluating the time decay of a modulation-caused electrical signal by comparing said decaying modulation-caused electrical signal and triggering an alarm signal when a predetermined deviation is exceeded between said decaying modulation-caused electrical signal and said reference signal.

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