INTRUSION ALARM SYSTEM

• US 3,761,909 A
• Filed: 12/30/1971
• Issued: 09/25/1973
• Est. Priority Date: 12/30/1971
• Status: Expired due to Term

• Current Assignee: John C. Schweitzer, Terry E. Tuttle
• Original Assignee: John C. Schweitzer, Terry E. Tuttle
• Inventors: Schweitzer, John C., Tuttle, Terry E.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/213,910
• Time in Patent Office: 635 Days
• Field of Search: 340/258A,258B,15,16R 331/116,154
• US Class Current: 367/94
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits

Abstract

An intrusion alarm system includes separate transmitting and receiving transducers. The system detects the presence of an intruder in a protected area by generating carrier waves in the area and sensing the modulation of the carrier waves reflected from the intruder. The system uses the receiving transducer as a frequency control device to generate an oscillatory signal of controlled amplitude at the resonant frequency of the receiving transducer. The transmitting transducer is excited by the oscillatory signal, thereby carrier waves are generated by the transmitting transducer at the resonant frequency of the receiving transducer.

Claims

1. An ultrasonic intrusion alarm system of the type which senses the presence of an intruder in a protected area by detecting the modulation of reflected carrier waves, comprising:

a receiving transducer having an ultrasonic resonant frequency;

a transmitting transducer capable of generating ultrasonic carrier waves at the ultrasonic resonant frequency of said receiving transducer, said transmitting and receiving transducers being positionable relative to each other so that ultrasonic carrier waves generated by said transmitting transducer are reflected from objects within a predetermined area to be protected to said receiving transducer;

oscillatory signal generating means connected to said receiving transducer for amplifying the reflected carrier waves sensed by said receiving transducer, said signal generating means being frequency controlled by said receiving transducer and operable to generate an amplified oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer;

output amplifier means connected between said oscillatory signal generating means and said transmitting transducer for amplifying the ultrasonic base frequency component of said oscillatory signal and exciting said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer; and

detecting means connected to said oscillatory signal generating means for detecting a modulation component of said oscillatory signal so as to detect the presence of an intruder within said protected area.

2. The invention defined in claim 1, including alarm means connected to said detecting means for indicating the presence of an intruder within said protected area.

3. The invention defined in claim 2 wherein the alarm means includes integration means adapted to integrate signal voltages from said detector means until the integrated signals are of a magnitude sufficient to actuate said alarm means, said integrator means having a discharge time constant which is modified according to receipt or nonreceipt of a signal from said detector such that the discharge time of the integrator during nonreceipt of a signal from said detector is substantially longer than the charge time and is approximately equal thereto during receipt of a signal from said detector.

4. The invention defined in claim 3 wherein the ratio of discharge time to charge time during nonreceipt of a signal from said detector is about two to one.

5. The invention according to claim 3 wherein said integrator means includes a changing capacitor having a charge and discharge path and switch means adapted to effectively switch additional resistance into the discharge path during nonreceipt of a signal from said detector.

6. The invention defined in claim 1, wherein said deecting means is operable to detect a frequency modulation component of said oscillatory signal thereby to detect the presence of an intruder in the protected area and including means for stabilizing the output level of said oscillatory signal generated by said oscillatory signal generating means, said output stabilizing means being operable to determine the output level of said oscillatory signal and vary the gain of said oscillatory signal generating means inversely in proportion thereto whereby to maintain the output level of said oscillatory signal at a predetermined level.

7. In an ultrasonic intrusion alarm system having separate receiving and transmitting transducers wherein said transmitting transducer is excited at an ultrasonic frequency to generate ultrasonic carrier waves in an area to be protected and the presence of an intruder in the protected area is sensed by detEcting the modulation of reflected ones of these carrier waves received by said receiving transducer, the improvement of signal generating means for connection between said receiving and transmitting transducers, said signal generating means being frequency controlled by said receiving transducer and operable to generate an oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer and excite said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer.

8. An ultrasonic intrusion alarm system of the type which senses the presence of an intruder in a protected area by detecting the modulation of reflected carrier waves, comprising:

a receiving transducer having an ultrasonic resonant frequency;

a transmitting transducer capable of generating ultrasonic carrier waves at the ultrasonic resonant frequency of said receiving transducer, said transmitting and receiving transducers being positionable relative to each other so that ultrasonic carrier waves generated by said transmitting transducer are reflected from objects within a predetermined area to be protected to said receivig transducer;

oscillatory signal generating means connected to said receiving transducer for amplifying the reflected carrier waves sensed by said receiving transducer and generating an amplified oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer, said oscillatory signal generating means including a transistor and an L-C resonant tank circuit, said transistor being connected as a tuned base-tuned collector amplifier with said tank circuit coupled to the collector electrode of said transistor and said receiving transducer coupled to its base electrode;

output amplifier means connected between said oscillatory signal generating means and said transmitting transducer for amplifying the ultrasonic base frequency component of said oscillatory signal and exciting said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer;

rectifier means also connected to said oscillatory signal generating means for rectifying said oscillatory signal;

means connected to said rectifier means for detecting a frequency modulation component of said rectified oscillatory signal thereby to detect the presence of an intruder in the protected area;

filter means also connected to said rectifier means for generating a DC control voltage proportional to the average value of said rectified oscillatory signal; and

gain control means connected between said filter means and said oscillatory signal generating means for controlling the gain of said oscillatory signal generating means inversely in proportion to the magnitude of said DC control voltage generated by said filter means whereby to maintain the output level of said oscillatory signal at a predetermined level.

9. The invention defined in claim 8, wherein said gain control means is a field effect transistor, said field effect transistor having its gate electrode connected to said filter means to receive said DC control voltage and its drain to source resistance path coupled to the emitter electrode of said transistor in said oscillatory signal generating means;

and including alarm means connected to said frequency modulation detecting means for indicating the presence of an intruder within said protected area.

10. An ultrasonic intrusion alarm system of the type which senses the presence of an intruder in a protected area by detecting the modulation of reflected carrier waves, comprising:

a receiving transducer having an ultrasonic resonant frequencY;

a transmitting transducer capable of generating ultrasonic carrier waves at the ultrasonic resonant frequency of said receiving transducer, said transmitting and receiving transducers being positionable relative to each other so that ultrasonic carrier waves generated by said transmitting transducer are reflected from objects within a predetermined area to be protected to said receiving transducer;

oscillatory signal generating means connected to said receiving transducer for amplifying the reflected carrier waves sensed by said receiving transducer and generating an amplified oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer, said oscillatory signal generating means including a transistor and an L-C resonant tank circuit, said transistor being connected as a tuned base-tuned collector amplifier with said tank circuit coupled to the collector electrode of said transistor and said receiving transducer coupled to its base electrode;

output amplifier means connected between said oscillatory signal generating means and said transmitting transducer for amplifying the ultrasonic base frequency component of said oscillatory signal and exciting said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base freuqency substantially equal to the ultrasonic resonant frequency of said receiving transducer; and

detecting means connected to said oscillatory signal generating means for detecting a modulation component of said oscillatory signal so as to detect the presence of an intruder within said protected area.

11. An ultrasonic intrusion alarm system of the type which senses the presence of an intruder in a protected area by detecting the modulation of reflected carrier waves, comprising:

a receiving transducer having an ultrasonic resonant frequency;

a transmitting transducer capable of generating ultrasonic carrier waves at the ultrasonic resonant frequency of said receiving transducer, said transmitting and receiving transducers being positionable relative to each other so that ultrasonic carrier waves generated by said transmitting transducer are reflected from objects within a predetermined area to be protected to said receiving transducer;

oscillatory signal generating means connected to said receiving transducer for amplifying the reflected carrier waves sensed by said receiving transducer and generating an amplified oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer;

output amplifier means connected between said oscillatory signal generating means and said transmitting transducer for amplifying the ultrasonic base frequency component of said oscillatory signal and exciting said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer; and

detecting means connected to said oscillatory signal generating means for detecting a modulation component of said oscillatory signal so as to detect the presence of an intruder within said protected area, said detecting means being operable to detect a frequency modulation component of said oscillatory signal thereby to detect the presence of an intruder in the protected area and including means for stabilizing the output level of said oscillatory signal generated by said oscillatory signal generating means, said output stabilizing means being operable to determine the output level of said oscillatory signal and vary the gain of said oscillatory signal generating means inversely in proportion thereto whereby to maintain the output level of said oscillatory signal at a predetermined level, said output stabilizing means including rectifier means connected to said oscillatory signal generating means for reCtifying said oscillatory signal, filter means connected to said rectifier means for generating a DC control voltage proportional to the average value of said rectified oscillatory signal, and gain control means connected between said filter means and said oscillatory signal generating means for controlling the gain of said oscillatory signal generating means as a function of the magnitude of said DC control voltage generated by said filter means.

12. The invention recited in claim 11, wherein said oscillatory signal generating means includes a transistor and an L-C resonant tank circuit, said transistor being connected as a tuned base-tuned collector amplifier with said tank circuit coupled to the collector electrode of said transistor and said receiving transducer coupled to its base electrode;

and said gain control means is a field effect transistor, said field effect transistor having its gate electrode connected to said filter means to receive said DC control voltage and its drain to source resistance path coupled to the emitter electrode of said transistor.

13. The invention recited in claim 12, including alarm means connected to said detecting means for indicating the presence of an intruder within said protected area.

14. An ultrasonic intrusion alarm system of the type which senses the presence of an intruder in a protected area by detecting the modulation of reflected carrier waves, comprising:

a receiving transducer having an ultrasonic resonant frequency;

a transmitting transducer capable of generating ultrasonic carrier waves at the ultrasonic resonant frequency of said receiving transducer, said transmitting and receiving transducers being positionable relative to each other so that ultrasonic carrier waves generated by said transmitting transducer are reflected from objects within a predetermined area to be protected to said receiving transducer;

oscillatory signal generating means connected to said receiving transducer for amplifying the reflected carrier waves sensed by said receiving, transducer and generating an amplified oscillatory signal having an ultrasonic base frequency substantially equal to the ultrasonic resonant frequency of said receiving transducer;

output amplifier means connected between said oscillatory signal generating means and said transmitting transducer for amplifying the ultrasonic base frequency component of said oscillatory signal and exciting said transmitting transducer therewith whereby said transmitting transducer generates ultrasonic carrier waves having a base frequency substantially equal to the ultrasonic resonant frequency of said transducer;

detecting means connected to said oscillatory signal generating means for detecting a modulation component of said oscillatory signal so as to detect the presence of an intruder within said protected area; and

, alarm means connected to said detecting means for indicating the presence of an intruder within said protected area, said alarm means including timer means adapted to recycle periodically upon receipt of an alarm signal from said detecting means and maintain the alarm means activated upon receipt of an alarm signal within the recycle period of the timer and to deactivate the alarm means in the absence of a further alarm signal within the recycle period.

15. The invention defined in claim 14 wherein the timer means includes operational amplifier means having an input R-C charging network which on being charged by receipt of an alarm signal drives the operational amplifier out of linear mode developing an output adapted to actuate said alarm means during the R-C network discharge period with a further alarm signal being received within the discharge period again charging the R-C network and maintaining said alarm means actuated and in the absence of a further alarm signal being received within the discharge period, allowing the operational amplifier to return to linear mode after a predetermined time period and deactivating said alaRm means.