US 4,290,126 AGranted

Ultrasonic intrusion alarm system

AssigneeGeneral Electric Company

InventorsRobert J. McFadyen, John F. Zeigler, III

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Abstract

An ultrasonic intrusion alarm system of the pulse-echo type transmits pulsed signals which are reflected by a reference surface. The resulting reference received pulsed signals appear as corresponding signals at the output of the system's receiver, which is gated on in coincidence with the arrival of said reference signals and is gated off at essentially all other times for minimum power consumption, the output signal state of said receiver being employed to cause the generation of an alarm signal upon the occurrence of an intrusion. The receiver includes an AGC amplifier network which exhibits a threshold voltage level that is a function of the signal strength of said reference signals which level is compared with the amplified received signals whereby said alarm is generated when said threshold level fails to be exceeded, such as due to an interruption of said signals.

Claims19

Dependent claims

An intrusion alarm system wherein transmitted pulsed signals are reflected by at least one surface including a reference surface within a protected area and the resulting received pulsed signals are employed to provide an indication of an intrusion within said protected area, comprising:

(a) transmitter means for periodically transmitting said transmitted pulsed signals,
(b) gate controlled receiver means, responsive to said received pulsed signals, for generating output signals that correspond to said received pulsed signals,
(c) first means for calculating the travel time of pulsed signals between said transmitter means and receiver means and for generating first control signals as a function of said travel time of received pulsed signals,
(d) second means, responsive to said first control signals, for periodically gating on said receiver means during brief periods that coincide with the calculated arrival of pulsed signals that are reflected by said reference surface, whereby said output signals are generated only upon the gated on operation of said receiver means, and
(e) third means, responsive to the output signal state of said receiver means during said brief periods, for generating an alarm signal that is indicative of an intrusion in the absence of said output signals and for preventing the generation of said alarm signal in the presence of said output signals.

2 more elements

(a) transmitter means for periodically transmitting said transmitted pulsed signals,
(b) receiver means responsive to said received pulsed signals for generating output signals that correspond to said received pulsed signals,
(c) first means for calculating the travel time of said received pulsed signals between said transmitter means and said receiver means,
(d) second means, responsive to said first means, for periodically enabling said receiver means so as to permit the generation of said output signals only upon the enabling of said receiver means, and
(e) third means, responsive to the output signal state of said receiver means during brief periods that coincide with the calculated arrival of received pulsed signals reflected by said reference surface for generating an alarm signal that is indicative of an intrusion in the absence of said output signals.

2 more elements

Dependencies are inferred from the claim text.