Distinguishing False Signals in Cable Locating

• US 20070170908A1
• Filed: 11/07/2006
• Published: 07/26/2007
• Est. Priority Date: 04/13/2005
• Status: Active Grant

• Current Assignee: Merlin Technologies Incorporated
• Original Assignee: Merlin Technologies Incorporated
• Inventors: Chau, Albert, Mercer, John
• Granted Patent: US 7,397,249 B2
• Time in Patent Office: Days
• US Class Current: 324/67
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G01V 3/165 operating with magnetic or electric fields produced or modified by the object or by the detecting device with electromagnetic waves G01V3/17
• CPC Class Codes: G01V 3/17 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

Discriminating between a cable locating signal and a false cable locating signal is described. A reference signal, which contains a locating signal frequency impressed on it, is transmitted in a way which provides for detection of a phase shift between the locating signal and the false locating signal. Based on the phase shift, a receiver is used to distinguish the locating signal from the false locating signal.

Claims

1. For use in a region which contains at least first and second in-ground cables, each of which cables includes an electrically conductive component such that, when the first cable is driven at a locating signal frequency to emit a locating signal in an electromagnetic form, the locating signal can be coupled to the second cable in a way which causes the second cable to generate a false locating signal in electromagnetic form, as part of an overall apparatus for discriminating between the locating signal and the false locating signal, a transmitter, comprising:

a frequency generator for generating said locating signal frequency; and

a transmitter configuration for transmitting a reference signal and for impressing the locating signal frequency thereon, in a way which provides for detection of a phase shift between the locating signal and the false locating signal.

2. The transmitter of claim 1 wherein said locating signal frequency, as contained by the reference signal, is at least approximately in a fixed phase relationship with said locating signal such that a detection of said phase shift can be based, at least in part, on said fixed phase relationship.

3. The transmitter of claim 2 further configured for driving said locating signal onto the first cable using inductive coupling and wherein said fixed phase relationship is at least approximately 90 degrees.

4. The transmitter of claim 1 wherein said fixed phase relationship is of a known magnitude and phase angle in relationship to said locating signal frequency.

5. The transmitter of claim 4 configured for driving the locating signal onto said first cable in a given way which establishes said fixed frequency relationship.

6. The transmitter of claim 5 configured for producing said reference signal including a carrier frequency that is modulated by said locating signal frequency.

7. The transmitter of claim 6 configured to produce a ratio of the carrier frequency to the locating signal frequency of at least 5.

8. The transmitter of claim 6 wherein the locating signal frequency is in a range from approximately 1 Hz to 80 KHz and the carrier frequency is in a range from approximately 10 Hz to 300 KHz.

9. The transmitter of claim 1 wherein said phase shift is in quadrature.

10. The transmitter of claim 1 including a telemetry arrangement for sending the reference signal to a receiver which forms part of the overall system.

11. The transmitter of claim 10 wherein said telemetry arrangement is configured to modulate an RF carrier with said reference signal and to transmit the RF carrier above ground for reception by said receiver.

12. For use in a region which contains at least first and second in-ground cables, each of which cable includes an electrically conductive component such that, when the first cable is driven at a locating signal frequency to emit a locating signal in an electromagnetic form, the locating signal can be coupled to the second cable in a way which causes the second cable to generate a false locating signal in electromagnetic form, as part of an overall apparatus for discriminating between the locating signal and the false locating signal, a receiver, comprising:

a receiver section for receiving a reference signal which contains said locating signal frequency impressed thereon, wherein a transmitter transmits said reference signal in a way which provides for detection of a phase shift between the locating signal and the false locating signal; and

a detector for detecting said phase shift and, based on said phase shift, distinguishes the locating signal from the false locating signal.

13. The receiver of claim 12 wherein the locating signal is electromagnetically coupled from the first cable to the second cable through the ground to cause the second cable to emit the false locating signal and wherein said receiver is configured to use said phase shift to

(a) recover the locating signal frequency from the reference signal, and

(b) synchronously detect

(i) said locating signal frequency, and

(ii) a selected frequency band, which includes said locating signal and said false locating signal, in a way which substantially rejects the false locating signal while providing an output responsive to the locating signal.

14. The receiver of claim 12 wherein said locating signal frequency, as contained by the reference signal, is at least approximately in a fixed phase relationship with said locating signal and detection of said phase shift by said receiver is based, at least in part, on said fixed phase relationship.

15. The receiver of claim 14 wherein said fixed phase relationship is at least approximately 90 degrees.

16. The receiver of claim 12 wherein said fixed phase relationship is of a known magnitude and phase angle in relationship to said locating signal frequency.

17. The receiver of claim 12 configured for receiving the reference signal as including a carrier frequency that is modulated by said locating signal frequency.

18. The receiver of claim 19 wherein a ratio of the carrier frequency to the locating signal frequency is at least 5 to 1.

19. The receiver of claim 17 wherein the locating signal frequency is in a range from approximately 1 Hz to 80 KHz and the carrier frequency is in a range from approximately 10 Hz to 300 KHz.

20. The receiver of claim 12 wherein said phase shift is in quadrature.

21. The receiver of claim 12 wherein the first cable and the second cable each include a distal end and the distal ends are resistively connected to one another such that the locating signal is resistively coupled from the first cable to the second cable to produce the false locating signal in an inverted phase relationship with respect to the locating signal and said receiver is configured to indicate a signal strength of one sign for the locating signal when an opposite sign signal strength is indicated for the false locating signal.

22. The receiver of claim 12 including a telemetry arrangement forming part of the receiver for receiving the reference signal.

23. The receiver of claim 22 wherein an RF carrier is modulated with said reference signal and transmitted above ground for reception by said receiver and said telemetry arrangement demodulates the RF carrier to recover the reference signal for use at the receiver.