Method for decoupling interference due to bleedover in metallic pipe and cable locators
First Claim
1. A receiver for a line locator, comprising:
- a first digital phase-locked loop coupled to receive an input signal and lock to a carrier frequency of the input signal;
a second digital phase-locked loop coupled to receive an FM signal from the first digital phase-locked loop and lock to a modulation frequency of the input signal; and
a quadrature demodulator coupled to receive the input signal and a frequency signal from the second digitor phase-locked loop and provide an in-phase signal.
4 Assignments
0 Petitions
Accused Products
Abstract
When cables run side by side over a longer distance, an alternating-current signal used for cable location can couple or ‘bleedover’ to neighboring cables. The coupled current flowing in the neighboring cable creates field distortion and makes position determination of the targeted cable difficult. The resulting magnetic field of both (or more) cables has a non-circular shape and is commonly known as a distorted field. Established methods for finding the position of the cable under investigation lead to inaccuracies or even wrong locates. The method described herein eliminates the field distortion that is due to the coupled cables by demodulating a phase reference signal placed on the cable by a transmitter into two signal strength constituents. The inphase signal represents the field strength of the targeted conductor and is substantially free of field distortion. The other quadrature signal contains the component of the field associated with distortion.
-
Citations
34 Claims
-
1. A receiver for a line locator, comprising:
-
a first digital phase-locked loop coupled to receive an input signal and lock to a carrier frequency of the input signal; a second digital phase-locked loop coupled to receive an FM signal from the first digital phase-locked loop and lock to a modulation frequency of the input signal; and a quadrature demodulator coupled to receive the input signal and a frequency signal from the second digitor phase-locked loop and provide an in-phase signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A locator, comprising
a detector system that provides at least one signal related to an electromagnetic field present at the locator; at least one receiver coupled to receive the at least one signal, each of the at least one receiver including a first digital phase-locked loop that locks to a carrier frequency of one of the at least one signal, a second digital phase-locked loop coupled to receive an FM signal from the first digital phase-locked loop and lock to a modulation frequency of the one of the at least one signal; and a quadrature demodulator coupled to receive the one of the at least one signal and a frequency signal from the second digital phase-locked loop and provide an in-phase signal; and a display coupled to receive the in-phase signal and provide user information to a user. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
- 24. A method of eliminating field distortion, comprising demodulating a phase reference signal placed on a target conductor by a transmitter into an in-phase and a quadrature signal.
-
26. A line locator system, comprising:
-
a transmitter coupled to provide a current signal to a target conductor, the current signal including at least one signal at a carrier frequency, the signal being modulated at a modulation frequency; and a locator, the locator, comprising a detector system that provides at least one signal related to an electromagnetic field present at the locator; at least one receiver coupled to receive the at least one signal, each of the at least one receiver including a first digital phase-locked loop that locks to the carrier frequency of one of the at least one signal, a second digital phase-locked loop coupled to receive an FM signal from the first digital phase-locked loop and lock to the modulation frequency of the one of the at least one signal; and a quadrature demodulator coupled to receive the one of the at least one signal and a frequency signal from the second digital phase-locked loop and provide an in-phase signal; and a display coupled to receive the in-phase signal and provide user information to a user.
-
-
27. A line locator system, comprising:
-
means for coupling a current signal to a target conductor; means for receiving a signal related to an electromagnetic field present at a locator; means for locking onto a carrier frequency of the current signal; means for locking onto an FM signal from the means for locking onto the carrier frequency; and means for performing a quadrature demodulation from a frequency signal from the means for locking onto the modulation signal.
-
-
28. A method of detecting signals associated with a target conductor while rejecting signals associated with bleedover to neighboring conductors, comprising:
-
providing an input signal in response to an electromagnetic field; locking to a carrier frequency of the input signal and providing a phase error signal; locking to an FM signal and providing a frequency signal; and mixing the frequency signal with the input signal to provide an in-phase signal. - View Dependent Claims (29, 30, 31, 32, 33)
-
-
34. A method of determining a depth of a target conductor, comprising:
-
providing a current signal on the target conductor, the current signal including a signal at a carrier frequency, the signal being modulated at a modulation frequency; determining a target line signal strength at a plurality of positions, the plurality of positions disposed along a line substantially perpendicular to a line of travel of the target conductor; and determining the depth from the target line signal strength at the plurality of positions, wherein the target line signal strength at each of the plurality of positions is determined by providing an input signal in response to an electromagnetic field at the position, locking to a carrier frequency of the input signal and providing an FM signal, locking to the modulation frequency in the FM signal and providing a frequency signal, mixing the frequency signal with the input signal to provide an in-phase signal, and determining the target line signal strength from the in-phase signal.
-
Specification