Method and system for reducing interference

• US 6,825,775 B2
• Filed: 08/01/2001
• Issued: 11/30/2004
• Est. Priority Date: 08/01/2001
• Status: Expired due to Fees

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Fling, Richard W., Hillman, Nicholas C.
• Primary Examiner(s): WONG, ALBERT KANG
• Application Number:
  US09/918,714
• Publication Number:
  US 20030058126A1
• Time in Patent Office: 1,217 Days
• Field of Search: 340/853.8, 340/856.3, 340/572.4, 324/326, 324/345, 733/82.R, 175/45, 175/50, 702/6, 702/104, 702/189, 702/194, 702/199
• US Class Current: 340/856.3
• 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: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

Method and systems for reducing effects of magnetic field interference that may interfere with a magnetic field signal generated at or near an underground object, where the magnetic field signal is used to monitor the location of the underground object. At least two different moving averages of a plurality of samples that are representative of a detected magnetic field signal strength are produce. Each of the different moving averages is a moving average of a different number of the plurality of samples. A respective quality metric (e.g., variance) is then determined for each of the different moving average. One of the moving averages is selected based on the determined quality metrics. Further signal processing is then performed using the selected moving average. For example, the selected moving average is used to monitor the location of the object.

Claims

1. A method for reducing effects of magnetic interference that may interfere with a magnetic field generated at or near an object with a device, comprising:

(a) producing at least two different moving averages of a plurality of samples that are representative of a detected magnetic field signal strength, wherein each of the different moving averages is a moving average of a different number of the plurality of samples;

(b) determining a respective quality metric for each of the different moving averages;

(c) selecting one of the moving averages based on the determined quality metrics;

(d) reducing the effects of the magnetic interference based on the selected moving average; and

(e) determining the location of the object with the device based in part upon the selected moving average.

2. The method of claim 1, wherein the magnetic interference that may interfere with the magnetic field generated at or near the object is periodic magnetic field interference, and wherein the moving average selected at step (c) is indicative of the magnetic field generated at or near the object.

3. The method of claim 1, further comprising the step of:

performing further signal processing using the selected moving average.

4. The method of claim 1, wherein each of the moving averages corresponds to a respective moving average length that is representative of the time interval during which the samples within the moving average were produced, each of the moving average lengths being different from one another, and wherein the moving average lengths collectively span the range of expected interference cycle periods.

5. The method of claim 4, further comprising the step of:

producing additional moving averages of additional samples representative of the magnetic field signal, the additional moving averages having a moving average length equal to the moving average length corresponding to the moving average selected at step (c).

6. The method of claim 5, further comprising the step of:

performing further signal processing using the selected moving average.

7. The method of claim 6, wherein step comprises using the selected moving average to monitor the location of the object.

8. The method of claim 1, wherein:

step (b) comprises determining a respective variance for each of the different moving averages, the quality metric for each of the moving averages comprising its respective variance; and

step (c) comprises selecting the one of the moving averages associated with the lowest variance.

9. The method of claim 1, wherein:

step (b) comprises (b.

     1) determining a respective maximum and minimum of each of the moving averages, and (b.2) determining a difference between the maximum and minimum of each of the moving averages, the quality metric for each of the moving averages comprising the difference between its respective maximum and minimum; and

step (c) comprises selecting the one of the moving averages associated with the lowest difference.

10. The method of claim 1, wherein:

step (b) comprises (b.1) determining a respective maximum and minimum of each of the moving averages, and (b.2) determining a ratio between the maximum and minimum of each of the moving averages, the quality metric for each of the moving averages comprising the ratio between its respective maximum and minimum; and

step (c) comprises selecting the one of the moving averages associated with the lowest ratio.

11. The method of claim 1, wherein step (a) comprises:

(a.1) producing a first moving average of the plurality of samples, the first moving average being a moving average of 60 of the plurality of samples;

(a.2) producing a second moving average of the plurality of samples, the second moving average being a moving average of 75 of the plurality of samples;

(a.3) producing a third moving average of the plurality of samples, the third moving average being a moving average of 90 of the plurality of samples; and

(a.4) producing a fourth moving average of the plurality of samples, the fourth moving average being a moving average of 105 of the plurality of samples.

12. The method of claim 11, wherein step (b) comprises determining a respective quality metric for each of the first, second, third and fourth moving averages.

13. The method of claim 12, wherein step (c) comprises selecting one of the first, second, third and fourth moving averages based on the determined quality metrics.

14. The method of claim 1, wherein step (a) comprises concurrently producing that at least two different moving averages.

15. The method of claim 1, wherein step (a) comprises serially producing that at least two different moving averages.

16. A subsystem for use in a device that monitors the location of an underground object based on an magnetic field generated at or near the object, the subsystem for reducing effects of magnetic interference that may interfere with the magnetic field generated at or near the object, the subsystem comprising:

means for producing at least two different moving averages of the plurality of samples that are representative of a detected magnetic field signal, wherein each of the different moving averages is a moving average of a different number of the plurality of samples;

means for determining a respective quality metric for each of the different moving averages;

means for selecting one of the moving averages based on the determined quality metrics;

means for reducing the effects of the magnetic interference in response to the selected moving average; and

means for determining the location of the object at least in part on the selected moving average.

17. The subsystem of claim 16, further comprising:

means for performing further signal processing using the selected moving average.

18. The subsystem of claim 17, wherein the means for performing further signal processing uses the selected moving average to monitor the location of the object.

19. The subsystem of claim 17, wherein each of the moving averages corresponds to a respective moving average length that is representative of the time interval during which the samples within the moving average were produced, each of the moving average lengths being different from one another.

20. The subsystem of claim 19, wherein the moving average lengths collectively span an operating bandwidth of the system.