MOTION DETECTION SYSTEM

• US 3,634,884 A
• Filed: 03/02/1970
• Issued: 01/11/1972
• Est. Priority Date: 03/02/1970
• Status: Expired due to Term

• Current Assignee: Vernon B. Ross
• Original Assignee: Vernon B. Ross
• Inventors: Ross, Vernon B.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Slobasky, Michael
• Application Number:
  US05/015,753
• Time in Patent Office: 680 Days
• Field of Search: 340/258,258A,26T,15.5,258B 343/5PD 325/8
• US Class Current: 342/28
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

A system for detecting human movement within a '"'"''"'"''"'"''"'"'protected'"'"''"'"''"'"''"'"' area comprising an ultrahigh frequency transmitter coupled to an antenna for continuously radiating electromagnetic waves of a sinusoidal waveform and for receiving such electromagnetic waves as are reflected from objects within the protected area. The transmitted and reflected waves are continuously algebraically summed and demodulated to produce a fluctuating direct current signal which in turn is filtered, amplified and amplitude detected to produce an alarm condition indicating signal only if an object is moving within the protected area and presents an '"'"''"'"''"'"''"'"'effective'"'"''"'"''"'"''"'"' signal-reflective area at least equivalent to a human. The alarm condition indicating signal is then monitored for repetitions indicative of human movement which if occurring activate an alarm or other support system.

Claims

1. A system for detecting motion of objects within an area protected by said system, comprising:

a transmitter for continuously generating an ultrahigh frequency signal of sinusoidal waveform;

an antenna coupled to said transmitter for continuously generating electromagnetic waves in response to said ultrahigh frequency signals to saturate said predetermined area and for continuously receiving electromagnetic waves of like frequency reflected from objects within said predetermined area to produce a reflected ultrahigh frequency signal of sinusoidal waveform;

circuit means for continuously algebraically combining said generated and reflected ultrahigh frequency signals to form a third ultrahigh frequency signal of varying amplitude;

detector means for continuously demodulating said third ultrahigh frequency signal to produce a fluctuating direct current signal;

means connected to said detector means for filtering low- and high-frequency components from said fluctuating direct current signal and producing a low-frequency alternating current signal;

threshold means for generating an alarm condition indicating signal when the amplitude of said fluctuating direct current signal exceeds a predetermined value indicative of movement of an object in the protected area presenting at least a predetermined minimum signal-reflective area, said threshold means including means responsive to positive- and negativegoing half-cycles of said alternating current signal for generating said alarm condition indicating signals when the magnitude of said alternating current exceeds a predetermined value during either said positive- or negative-going halfcycles; and

means for monitoring said alarm condition indicating signals for repetitions thereof within a predetermined time interval and for developing an alarm-actuating signal in response thereto.

2. The system of claim 1 wherein said means responsive to positive- and negative-going half-cycles of said alternating current signal comprises a biphase amplifier means for developing first and second AC signals 180* out of phase with each other, high-gain amplifier means with positive predetermined voltage thresholds for receiving said first and second AC signals and for generating pulse signals when the magnitude of said first and second signals exceed said voltage thresholds, and an OR gate for receiving said pulse signals from said high-gain amplifier means for developing said alarm condition indicating signal upon receipt of a pulse from either of said high-gain amplifier means.

3. The system of claim 1 wherein said means for monitoring said alarm condition indicating signals comprises first circuit means comprising a first monostable multivibrator and a differentiator responsive to each alarm condition indicating signal for developing a first electrical signal of relatively short time duration, said circuit means Comprising a second monostable multivibrator and integrator responsive to said first electrical signal for developing a second electrical signal of relatively long time duration at the termination of a first electrical signal and means responsive to a combination of said first and second electrical signals for developing said alarm-actuating signal and comprising an AND gate connected to said first monostable multivibrator and to said integrator and a third monostable multivibrator connected to an output of said AND gate.

4. The system of claim 3 including circuit means for blocking said alarm-actuating signal from actuating an alarm system comprising a second AND gate connected to an output of said third monostable multivibrator, a fourth monostable multivibrator connected to an input to said second AND gate, a power supply, a normally open switch between said power supply and an input to said fourth monostable multivibrator, said fourth monostable multivibrator having a predetermined period of operation after closing of said switch during which it blocks said second AND gate.