Distinguishing false signals in cable locating

• US 7,884,610 B2
• Filed: 07/30/2009
• Issued: 02/08/2011
• Est. Priority Date: 04/13/2005
• Status: Expired due to Fees

• Current Assignee: Merlin Technologies Incorporated
• Original Assignee: Merlin Technologies Incorporated
• Inventors: Mercer, John E., Chau, Albert W.
• Primary Examiner(s): Patidar; Jay M
• Application Number:
  US12/512,853
• Publication Number:
  US 20090289634A1
• Time in Patent Office: 558 Days
• Field of Search: None
• US Class Current: 324/326
• 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. In a region which includes 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, a method for discriminating between the locating signal and the false locating signal, said method comprising:

generating a reference signal;

impressing the locating signal frequency on the reference signal;

transmitting the reference signal, which contains said locating signal frequency impressed thereon, in a way which provides for detection of a phase shift between the locating signal and the false locating signal; and

based on said phase shift, using a receiver, distinguishing the locating signal from the false locating signal.

2. The method of claim 1 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 distinguishing includes recovering the locating signal frequency from the reference signal and synchronously detecting the locating signal frequency and 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.

3. 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, an apparatus for discriminating between the locating signal and the false locating signal, said apparatus comprising:

a transmitter for generating said locating signal frequency and for transmitting a reference signal, which contains said locating signal frequency impressed thereon, in a way which provides for detection of a phase shift between the locating signal and the false locating signal; and

a receiver for detecting said phase shift and for distinguishing the locating signal from the false locating signal based on the phase shift.

4. The apparatus of claim 3 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 us configured to recover the locating signal frequency from the reference signal and to synchronously detect said locating signal frequency and 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.