Piezoelectric cable sensor having remote monitoring self test capability

• US 20020007660A1
• Filed: 05/14/2001
• Published: 01/24/2002
• Est. Priority Date: 05/12/2000
• Status: Abandoned Application

• Current Assignee: Richard Hunter Brown
• Original Assignee: Richard Hunter Brown
• Inventors: Brown, Richard Hunter
• Application Number:
  US09/854,792
• Publication Number:
  US 20020007660A1
• Time in Patent Office: Days
• US Class Current: 73/1.82
• CPC Class Codes: G08B 13/122 for a perimeter fence features peculiar to electrified fences A01K3/00
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults
• CPC Class Codes: H10N 30/60 having a coaxial cable structure

Abstract

A sensor system comprising two or more electrically-independent piezoelectric cables, secure at intervals to a common rigid or semi-rigid structure or to themselves and spaced apart from one another, with one cable at any given instant coupled to an electrical drive signal and acting as a transmitter, the other cable or cables acting as a receiver and connected to electronic detection circuitry, such that a mechanical vibration signal is launched by the transmitter and detected by the receiver to enable the detection function of the other cable or cables as receivers to be checked.

Claims

1. A sensor system comprising:

a first length of piezoelectric cable secured to a first portion of a rigid or semi-rigid structure;

a second length of piezoelectric cable secured to a second portion of a rigid or semi-rigid structure;

wherein the first and second lengths of piezoelectric cable are electrically independent of one another and physically separated from one another;

a drive circuit selectively coupled to the first length of cable for transmitting a drive signal to the first length to cause the first length to transmit acoustic signals; and

a processor selectively coupled to the second length of cable for receiving signals detected by the second length of cable in response to the acoustic signals transmitted by the first length of cable to determine responsivity of the second length of cable.

2. The system of claim 1, wherein the drive signal includes spectral frequencies ranging between 500 Hz and 5000 Hz.

3. The system of claim 1, further comprising a controller for controlling the rate at which the drive circuit transmits the drive signal.

4. The system of claim 1, further comprising a switching mechanism first and second ports in electrical communication with the drive circuit and the processor, respectively, and third and fourth ports in electrical communication with the first and second lengths of cable, respectively, for selectively switching the communication paths of the first and second lengths of cable with the drive circuit and processor to enable switching of the transmitter and receiver functions of the first and second lengths of cable.

5. The system of claim 4, wherein the switching is performed on a periodic basis.

6. The system of claim 4, wherein the switching is performed on a non-periodic basis.

7. A sensor system comprising:

two or more electrically-independent piezoelectric cables, secure at intervals to a common rigid or semi-rigid structure or to themselves and spaced apart from one another, with one cable at any given instant coupled to an electrical drive signal and acting as a transmitter, the other cable or cables acting as a receiver and connected to electronic detection circuitry, such that a mechanical vibration signal is launched by the transmitter and detected by the receiver to enable the detection function of the other cable or cables as receivers to be checked.

8. The system of claim 7, wherein the one cable operating as a transmitter is driven continuously to provide continuous checking of the receiver cable or cables.

9. The system of claim 7, wherein the one cable operating as a transmitter is driven intermittently to provide intermittent checking of the receiver cable or cables.

10. The system of claim 7, further comprising a switching mechanism for switchably coupling respective ones of the two or more piezoelectric cables to the corresponding electrical drive signal and electronic detection circuitry to selectively check the detection function of each of the two or more piezoelectric cables.

11. A method for remotely monitoring a sensor system comprising two or more electrically-independent piezoelectric cables, secured at intervals to a common rigid or semi-rigid structure or to themselves and spaced apart from one another, said method comprising:

driving one of the cables with a test signal to cause the cable to operate as a transmitter to

transmit an acoustic signal indicative of the test signal; and

monitoring the output of at least another one of the cables to determine whether the at least

one other cable detects the acoustic signal resulting from the drive signal.

12. The method of claim 11, wherein the step of monitoring comprises amplifying and processing responses from the at least one other cable and comparing with the test signal to determine signal detection.

13. The method of claim 11, further comprising the step of selectively switching the driving and monitoring functions of the two or more piezoelectric cables in a predetermined manner to selectively monitor each of the two or more piezoelectric cables.

14. The method of claim 11, wherein the step of driving one of the cables comprises transmitting an electrical drive signal comprising at least one electrical pulse of a given amplitude and frequency to cause the one cable to transmit the acoustic signal;

and

wherein the step of monitoring comprises receiving the output from another one of the cables, filtering the output to obtain a filtered signal characteristic of an amplitude and frequency range, and comparing the filtered signal with the drive signal.

15. The method of claim 14, wherein the step of filtering further comprises performing spectral processing of the received output.

16. In a security system comprising two or more electrically-independent piezoelectric cables, secured at intervals to a common rigid or semi-rigid structure or to themselves and spaced apart from one another, for detecting vibrational signals incident thereon indicative of an intrusion attempt and transmitting an electrical signal in response thereto, and a detection circuit coupled to the piezoelectric cables for comparing the electrical signal received from the detecting cable with a threshold value to determine whether or not an intrusion attempt has occurred, a method for remotely monitoring the integrity of the security system comprising:

driving one of the cables with a test signal to cause the cable to operate as a transmitter to transmit an acoustic signal indicative of the test signal; and

monitoring the output of at least another one of the cables to determine whether the at least one other cable detects the acoustic signal resulting from the drive signal.

17. The method of claim 16, wherein the step of monitoring comprises analyzing the spectral content of the detected signal to determine correspondence to the test signal.

18. The method of claim 16, wherein the test signal has an amplitude sufficiently less than the intrusion detection threshold to enable simultaneous intrusion detection and integrity monitoring.

19. The method of claim 16, wherein the test signal has a bandwidth outside the bandwidth associated with determining an intrusion detection so as to enable simultaneous intrusion detection and integrity monitoring.

20. The method of claim 16, further comprising the step of selectively switching the driving and monitoring functions of the two or more piezoelectric cables in a predetermined manner to selectively monitor the integrity of each of the two or more piezoelectric cables.

21. A sensor system comprising:

a first length of piezoelectric cable secured to a first portion of a rigid or semi-rigid structure;

a second length of piezoelectric cable secured to a second portion of a rigid or semi-rigid structure;

wherein the first and second lengths of piezoelectric cable are electrically independent of one another and physically separated from one another;

a drive circuit for transmitting a test signal to one of the first or second lengths of piezoelectric cable;

a processor for receiving an output from the other one of the first or second lengths of piezoelectric cable and comparing with a predetermined threshold to determine the responsivity of that length of cable; and

a switching mechanism for selectively coupling one of the first and second lengths of piezoelectric cable to the drive circuit and the other length of piezoelectric cable to the processor for enabling acoustic signals transmitted by the length of piezoelectric cable coupled to the drive circuit in response to the test signal to be detected by the length of cable coupled to the processor.