ULTRASONIC ALARM CIRCUIT

• US 3,801,977 A
• Filed: 12/07/1971
• Issued: 04/02/1974
• Est. Priority Date: 12/07/1971
• Status: Expired due to Term

• Current Assignee: Elektrowatt AG Bellerivestrasse
• Original Assignee: William L. Cotter
• Inventors: Cotter, William L.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/205,599
• Time in Patent Office: 847 Days
• Field of Search: 340/258A,27C
• US Class Current: 367/94
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

Abstract

The circuit is preferably located within an area that is to be secured, is of the type that transmits an ultrasonic signal to establish an ultrasonic wave pattern in the area, and includes doppler phase detection circuitry responsive to both the transmitted and received ultrasonic signals for providing a doppler signal of a frequency corresponding to the velocity of motion in the area. In one embodiment the circuit includes a threshold filter and a detection filter each having different frequency responses, both coupling to separate inputs of a differential detector, an output accumulator circuit coupled from the differential detector, and a high pass filter for inhibiting the output accumulator circuit upon receiving signals of above a predetermined frequency, but inhibiting the accumulator for only up to a preselected time interval. In another embodiment of the invention the circuit includes, in addition to a threshold filter, detection filter, differential detector, and output accumulator circuit, a separate cancel channel and associated receiver transducer responsive preferably to higher frequency noise signals at frequencies just below the frequency of the transmitted ultrasonic signal to inhibit the output accumulator upon receipt of such signals but only for a preselected time interval.

Claims

1. An ultrasonic intruder detection circuit for use in a secured area comprising:

means for transmitting an ultrasonic signal to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

a difference circuit;

first frequency responsive means coupled from said means for registering to a first input of said difference circuit for establishing a frequency dependent threshold signal at the first input;

second frequency responsive means coupled from said means for registering to a second input of said difference circuit for establishing a frequency dependent detection signal at the second input;

output alarm means coupled from an output of said difference circuit responsive to said detection signal exceeding said threshold signal for providing an alarm condition, and third frequency responsive means coupled from said means for registering to said output alarm means for passing doppler signals of a frequency higher than the frequency of an intruder doppler signal to thereby inhibit said output alarm means and prevent the generation of an alarm condition for a predetermined time duration.

2. The circuit of claim 1 wherein said output alarm means includes an accumulator circuit having a charging means that is charging during the predetermined time duration and means coupled to the charging means and responsive to the termination of the predetermined timE duration for generating an alarm condition.

3. The circuit of claim 1 wherein said means for transmitting an ultrasonic signal includes an oscillator circuit operating at a carrier frequency and said means for registering a doppler signal includes a phase detector coupled from and responsive to both said oscillator and said means for receiving for providing a modulated carrier signal modulated at a rate corresponding to the velocity of motion in the area.

4. The circuit of claim 3 comprising a low pass filter coupled between said phase detector and said first and second frequency responsive means for removing the carrier frequency from the modulated signal to provide the doppler signal.

5. The circuit of claim 1 wherein each said first and second frequency responsive means includes an RC filter network.

6. The circuit as claim 5 wherein said first frequency responsive means includes a notch filter having a decreased gain at the middle of a predetermined range of frequencies comprising an intruder frequency band in comparison to the gain of the second frequency responsive means.

7. The circuit of claim 6 wherein said intruder frequency band extends between 12 hertz and 250 hertz.

8. The circuit of claim 5 wherein said second frequency responsive means includes a band pass filter having a constant gain higher than the gain of the first frequency responsive means over the range of frequencies commencing at 12 Hertz and ending at 250 Hertz.

9. The circuit of claim 1 wherein said first and second frequency responsive means each include a filter network and each have a low frequency operating point where their gains are equal and a high frequency operating point where their gains are equal, the gain of the second frequency responsive means being greater in the frequency range between said first and second operating points than the gain of the first frequency responsive means.

10. The circuit of claim 1 wherein said first frequency responsive means includes a notch filter, said second frequency responsive means includes a band pass filter, and further comprising a high pass filter coupled from said means for registering to said output alarm means for passing signals above a frequency of 1,000 hertz.

11. The circuit of claim 10 wherein said output alarm means includes an AND circuit coupled from said difference circuit and an accumulator circuit coupled from the AND circuit.

12. The circuit of claim 11 comprising a detection circuit coupled from said high pass filter and having a first line coupled to the AND circuit for enabling the AND circuit in the absence of a passing of signals above 1,000 hertz, and a slow charge line coupled to the accumulator for charging the accumulator at a slower rate than when it is charged via the AND circuit in the presence of signals above 1,000 hertz.

13. The circuit of claim 12 wherein said AND circuit is inhibited during the time that said high pass filter is passing signals above 1,000 hertz.

14. An ultrasonic intruder detection circuit for use in a secured area comprising:

means for transmitting an ultrasonic signal to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

first frequency responsive means coupled from said means for registering for passing doppler signals in the expected intruder frequency range;

second frequency responsive means coupled from said means for registering for passing doppler signals above the expected intruder frequency range; and

output timing means having a first input coupled from said first frequency responsive means and a second input coupled from said second frequency responsive means;

said output timing means responsive to said first frequency responSive means for generating an alarm condition after a first predetermined time period. said output timing means responsive to said second frequency responsive means for generating an alarm condition after a second predetermined time period which is longer than said first predetermined time period.

15. The circuit of claim 14 wherein said output timing means includes a charge accumulator circuit having a capacitor means and means for charging said capacitor means at two different charge time constants.

16. The circuit of claim 15 comprising an AND circuit responsive to both said first and second frequency responsive means for permitting a charging of said capacitor means over the first predetermined time period in the absence of signals from said second frequency responsive means detected above a frequency of 250 Hertz.

17. The circuit of claim 16 wherein said AND circuit is inhibited in the presence of signals detected above a predetermined range of frequencies comprising an intruder frequency range and set accumulator is charged over the second predetermined time period.

18. An ultrasonic intruder detection circuit for use in a secured area comprising:

means for transmitting an ultrasonic signal of a first frequency to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

output alarm means coupled from said means for registering and responsive to a predetermined frequency band of said doppler signal for providing an alarm condition;

transducer means responsive to signals of said first frequency and coupled to said output alarm means for inhibiting said alarm condition for a preselected time interval.

19. The circuit of claim 18 wherein said means for registering includes a phase detector responsive to both said means for transmitting and said means for receiving for providing said doppler signal and amplifying means.

20. The circuit of claim 19 comprising an automatic gain control loop coupled from said amplifying means to said phase detector for controlling the DC value of the doppler signal.

21. The circuit of claim 20 wherein said means for transmitting includes an oscillator and said phase detector includes a field effect transistor which is cyclically turned off by the oscillator, the on-time resistance of the transistor being controlled by the automatic gain control loop.

22. An ultrasonic intrusion detection system for use in a secured area comprising:

means for transmitting an ultrasonic signal to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

first frequency responsive means coupled from said means for registering for establishing a frequency dependent threshold signal;

second frequency responsive means coupled from said means for registering for establishing a frequency dependent detection signal;

detection means for receiving said threshold and detection signal;

output alarm means coupled from an output of said detection means responsive to said detection signal exceeding said threshold signal for providing an alarm condition; and

first and second averaging means coupled respectively from said first and second frequency responsive means to said detection means.

23. The system of claim 22 wherein each said averaging means includes a time integrating circuit.

24. The system of claim 22 wherein each said averaging means includes means defining a charging time constant.

25. The system of claim 24 wherein the charging time constant of said averaging means of said second frequency responsive meaNs is less than the time constant of the averaging means of the first frequency responsive means.

26. The system of claim 25 wherein each said averaging means includes a rectifying means and capacitor means.

27. An ultrasonic intrusion detection system for use in a secured area comprising:

means for transmitting an ultrasonic signal to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

first frequency responsive means coupled from said means for registering for establishing a frequency dependent threshold signal;

second frequency responsive means coupled from said means for registering for establishing a frequency dependent detection signal;

detection means for receiving said threshold and detection signals; and

output alarm means coupled from an ouput of said detection means responsive to said detection signal exceeding said threshold signal for providing an alarm condition;

said first and second frequency responsive means each including filter means having a low frequency operating point wherein their gains are equal, the gain of the first frequency responsive means being greater at frequencies below said low frequency operating point.

28. The system of claim 27 wherein said filter means each include a filter network and each have a high frequency operating point wherein their gains are equal, the gain of the second filter network being greater in the frequency range between said low and high operating points than the gain of the first filter network.

29. An ultrasonic intrusion detection system for use in a secured area comprising:

means for transmitting an ultrasonic signal to establish an ultrasonic wave pattern in the area;

means for receiving the reflected ultrasonic signal;

means responsive to said transmitting and said receiving means for registering a doppler signal of a frequency corresponding to the velocity of motion in the area;

first frequency responsive means coupled from said means for registering for establishing a frequency dependent threshold signal;

second frequency responsive means coupled from said means for registering for restablishing a frequency dependent detection signal;

detection means for receiving said threshold and detection signals;

output alarm means coupled from an output of said detection means responsive to said detection signal exceeding said threshold signal for providing an alarm condition; and

third frequency responsive means responsive to signals of a frequency higher than the frequency corresponding to an intruder, said third frequency responsive means coupled to said output alarm means to inhibit said ouput alarm means and prevent an alarm condition.

30. The system of claim 29 wherein said third frequency responsive means includes a transducer means.

31. The system of claim 30 wherein said transducer means is responsive to signals of a frequency on the order of the frequency of the transmitted ultrasonic signal.

32. The system of claim 29 wherein said third frequency responsive means includes a filter network.