Device for locating objects that emit electromagnetic signals

• US 5,920,194 A
• Filed: 11/04/1996
• Issued: 07/06/1999
• Est. Priority Date: 05/06/1994
• Status: Expired due to Term

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Lewis, Andrew B, Cottle, John R, Cooper, Graham R
• Primary Examiner(s): Patidar, Jay M.
• Application Number:
  US08/737,060
• Time in Patent Office: 974 Days
• Field of Search: 324/327, 324/326, 324/329, 324/328, 324/345, 324/66, 324/67
• US Class Current: 324/326
• CPC Class Codes: G01V 3/06 using ac
• 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

Abstract

A locator such as a ground penetration probe (24) has spaced antennae (21,22,23) therein which detect electromagnetic signals from an object (26) such as a buried cable. By analyzing the electromagnetic signals using a suitable processor (25) it is possible to determine the separation of the locator and object (26), both in terms of the direction (X) corresponding to the spacing of the antennae (21,22,23) and the perpendicular direction (Y) to the object (26). This then permits a display to be generated showing visually the separation of the locator and the object (26). If the locator incorporates a tilt sensor, the processor (25) can then compensate for tilting of the locator, and determine the vertical and horizontal separation of the locator and the object (26). A confidence measurement may be obtained by measuring the separation of the locator and object (26) at one position, predicting the separation of the locator and object (26) at a second position, and comparing the predicted and measured separations.

Claims

1. A locator comprising:

a ground penetration probe having at least two antennae therein with a predetermined separation therebetween, the antennae being arranged to detect electromagnetic signals from a conductor of an object;

means for analyzing the electric signals to determine the separation of the locator and object both in the direction (x) of the separation of the antennae and the direction (y) transverse thereto; and

means for controlling the drilling force of the round penetration probe depending on the separation of the ground penetration probe and the object.

2. A locator according to claim 1, wherein the ground penetration probe further comprises a removable sheath for receiving said probe.

3. A locator according to claim 2, having three antennae.

4. A locator according to claim 3, wherein the analyzing means is arranged to analyze the electromagnetic signals detected by a first and a second antenna of said three antennae when the locator and the object have a separation greater than a predetermined value, and to analyze the electromagnetic signals from the first and the third antenna of said three antennae when the locator and the object have a separation less than said predetermined value.

5. A locator according to claim 4, having a transmitter for inducing signals into the conductor of the underground object.

6. A locator according to claim 5, having means for generating a display showing the spatial relationship of the probe and the object, based on the electromagnetic signals.

7. A locator according to claim 6, wherein the analyzing means is arranged to predict the electromagnetic signals detectable by said antennae corresponding to a different separation of the locator and object.

8. A locator according to claim 7, further including a tilt sensor.

9. A locator according to claim 8, wherein the analyzing means is arranged to compensate for perturbations or asymmetries in the electromagnetic signals in determining the separation of the locator and the object.

10. A locator according to claim 9, wherein each antenna comprises at least two mutually perpendicular coils.

11. A locator according to claim 10, wherein each antenna comprises three mutually perpendicular coils.

12. A locator according to claim 11, wherein the axes of the coils intersect.

13. A locator according to claim 11, wherein the axes of any two coils do not intersect and the analyzing means is arranged to compensate for the relative displacement of the coils in determining the separation of the locator and the object.

14. The combination of a locator according to claim 13 and an object, the object having at least one active marker forming said conductor, said active marker being arranged to generate a coded signal, said locator having means for generating an input signal to said active marker for triggering said coded signal and means for detecting said coded signal from said active marker.

15. A locator according to claim 6, wherein the means for generating the display is a head-up display for an operator of the probe.

16. The combination of a locator according to claim 15 and at least two objects, each object having a conductor and each conductor generating electromagnetic signals, the electromagnetic signals of each conductor being different, wherein the means for generating a display is arranged to show the spatial relationship of the two objects.

17. A method of locating an object using a locator having at least two antennae, comprising the steps of:

(a) detecting electromagnetic signals from a conductor of the object using said antennae when the locator is in a first position;

(b) moving said locator from said first position to a second position; and

(c) detecting the electromagnetic signals from the conductor of the object using said antennae when the locator is in the second position;

wherein;

the electromagnetic signals from the conductor of the object detectable by said antennae when said locator is in the second position are predicted on the basis of the electromagnetic signals detected in the first position; and

the predicted electromagnetic signals and the electromagnetic signals detected when the locator is in the second position are compared.

18. A method according to claim 17, wherein the locator is tilted from the first position to the second position, and the tilt is measured by a tilt sensor, and the measured tilt is used in the predictions of the electromagnetic signals detectable by the locator in the second position.