US 4,727,522 AGranted

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

AssigneeCerberus AG

InventorsPeter Steiner, Rudolf Genahr, David Siegwart

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Abstract

In an ultrasonic alarm installation ultrasonic waves are continuously emitted into a monitored region and a frequency shift due to a moving object, e.g. an intruder, by virtue of the Doppler effect is evaluated for giving an alarm signal. The function control in this installation occurs during a test phase by means of brief aperiodic modulation of the emitted ultrasonic waves. The resulting brief frequency broadening generates in the same evaluating circuit a signal if the installation is functioning correctly. The time duration of the aperiodic modulation is selected to be so short that no standing waves can form, so that the function control can also work faultlessly if the installation, because of vectorial addition of the received ultrasonic waves, accidentally is in an insensitive state. Thus even coverings of the ultrasonic transmitter during a sabotage attempt can be recognized and distinguished from an insensitive state.

Claims21

Dependent claims

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 reflected from said 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 in said electrical evaluation circuit and thereby triggering 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 entailing aperiodically modulating said emitted ultrasonic waves for a predetermined modulation time interval such that the frequency spectrum of said emitted ultrasonic waves includes said predetermined frequency deviation;
receiving said emitted aperiodically modulated ultrasonic waves of said frequency spectrum including said predetermined frequency deviation and originating from said monitored region, by means of said ultrasonic receiver and thereby converting said received aperiodically modulated ultrasonic waves into an electrical signal;
feeding said electrical signal caused by said received aperiodically modulated ultrasonic waves to said electrical evaluation circuit;
and
processing said electrical signal caused by said received aperiodically modulated ultrasonic waves of said frequency spectrum including said predetermined frequency deviation and thereby selectively triggering, by means of said electrical evaluation circuit, one of a "ready-to-function" signal and said alarm signal.

8 more elements

A circuit arrangement for testing an ultrasonic alarm installation containing an ultrasonic transmitter for emitting ultrasonic waves of a predetermined frequency into a region to be monitored, an ultrasonic receiver for receiving ultrasonic waves reflected from said region and converting said received ultrasonic waves into an electrical signal, an electrical evaluation circuit connected to said ultrasonic receiver for processing said electrical signal and triggering an alarm signal upon a predetermined frequency deviation of said received ultrasonic waves from said ultrasonic waves emitted by said ultrasonic transmitter, said circuit arrangement comprising:

modulating means for aperiodically modulating the emitted ultrasonic waves for a predetermined modulation time interval during a test phase of the operation of the ultrasonic alarm installation and thereby producing ultrasonic waves of a frequency spectrum including said predetermined frequency deviation during such test phase;
and
the electrical evaluation circuit processing, during said test phase, an electrical signal caused by the received aperiodically modulated ultrasonic waves of said frequency spectrum including said predetermined frequency deviation and selectively triggering one of a "ready-to-function" signal and the alarm signal.

Dependencies are inferred from the claim text.