Method of determining distance to a ferrous material

• US 8,314,608 B2
• Filed: 06/30/2010
• Issued: 11/20/2012
• Est. Priority Date: 06/30/2010
• Status: Active Grant

• Current Assignee: Caterpillar Sarl (Caterpillar Incorporated)
• Original Assignee: David R. Hall
• Inventors: Hall, David R., Wahlquist, David C., Hall, Huntington Tracy
• Primary Examiner(s): Aurora, Reena
• Application Number:
  US12/827,525
• Publication Number:
  US 20120001621A1
• Time in Patent Office: 874 Days
• Field of Search: 324/207.13, 324/207.15, 324/207.16, 702/104
• US Class Current: 324/207.13
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01R 33/028 Electrodynamic magnetometers

Abstract

In one aspect of the present invention a method of determining a distance to a ferrous material comprises providing a plurality of magnetometers spaced at varying distances from a ferrous material, detecting a ferrous material with each of the plurality of magnetometers individually, establishing one of the plurality of magnetometers as a primary magnetometer, obtaining sensor readings from each of the plurality of magnetometers, forming a first ratio of the differences in the sensory readings of the primary magnetometer to the sensory readings of the other magnetometers, forming a second ratio of the differences in inversely cubed distances to the ferrous material from the primary magnetometer to inversely cubed distances to the ferrous material from the other magnetometers, setting the first ratio and the second ratio equal to each other, and calculating the distance to the ferrous material from the plurality of magnetometers.

Claims

1. A method of determining a distance to a ferrous material comprising:

providing a plurality of magnetometers spaced at varying distances from a ferrous material;

detecting a ferrous material with each of the plurality of magnetometers individually;

establishing one of the plurality of magnetometers as a primary magnetometer;

obtaining sensor readings from each of the plurality of magnetometers;

forming a first ratio between the difference in the sensor reading of the primary magnetometer and a sensor reading from a first magnetometer of the plurality of magnetometers and the difference in the sensor reading of the primary magnetometer and a sensor reading from a second magnetometer of the plurality of magnetometers;

forming a second ratio between the difference of a distance to a ferrous material from the primary magnetometer inversely cubed and the distance to a ferrous material from the first magnetometer inversely cubed and the difference of the distance to a ferrous material from the primary magnetometer inversely cubed and the distance to a ferrous material from the second magnetometer inversely cubed;

setting the first ratio and the second ratio equal to each other; and

calculating a distance to the ferrous material from the plurality of magnetometers.

2. The method of claim 1, further comprising determining a relative strength of a magnetic field of the ferrous material.

3. The method of claim 1, further comprising determining a relative strength of an ambient magnetic field.

4. The method of claim 1, wherein the spacing of the plurality of magnetometers is vertical with respect to one another.

5. The method of claim 4, wherein providing a plurality of magnetometers comprises providing a plurality of horizontal arrays of pluralities of vertically spaced magnetometers.

6. The method of claim 5, wherein the providing the plurality of horizontal arrays comprises positioning the horizontal arrays side by side.

7. The method of claim 5, wherein the providing the plurality of horizontal arrays comprises positioning the horizontal arrays overlapping each other.

8. The method of claim 5, wherein providing a plurality of magnetometers comprises providing a virtual magnetometer from two horizontally adjacent magnetometers on a horizontal array.

9. The method of claim 8, wherein providing a virtual magnetometer comprises obtaining a sensory reading for the virtual magnetometer by summing the sensor readings from the two horizontally adjacent magnetometers and then dividing the sum by the total number of sensor readings that are being summed.

10. The method of claim 8, wherein providing a virtual magnetometer comprises obtaining a sensory reading for the virtual magnetometer by summing each of the sensor reading from the two horizontally adjacent magnetometers multiplied by the total distance between the adjacent magnetometers minus the distance to the virtual magnetometer from that magnetometer and then dividing the entire sum by the total distance.

11. The method of claim 8, wherein providing a virtual magnetometer comprises obtaining a sensory reading for the virtual magnetometer by forming a cubic function based on restrictions that the cubic function passes through the sensory reading of a first magnetometer of the two horizontally adjacent magnetometers, has a slope at the sensory reading of the first magnetometer equal to a slope passing through the sensory readings of a magnetometer horizontally adjacent to the first magnetometer and a second magnetometer of the two horizontally adjacent magnetometers, passes through the sensory reading of the second magnetometer, and has a slope at the sensory reading of the second magnetometer equal to a slope passing through the sensory readings of a magnetometer horizontally adjacent to the second magnetometer and the first magnetometer.

12. The method of claim 5, further comprising determining a size of the ferrous material from the plurality of horizontal arrays.

13. The method of claim 5, further comprising determining a location of an edge of the ferrous material from the plurality of horizontal arrays.

14. The method of claim 1, wherein the spacing of the plurality of magnetometers is such that each magnetometer of the plurality of magnetometers detects at least 10 percent of the sensor reading due to a magnetic field from the ferrous material of a magnetometer disposed closest to the ferrous material.

15. The method of claim 1, wherein the obtaining sensor readings from each of the plurality of magnetometers comprises obtaining sensor readings of an absolute magnetic field which comprises the sum of readings from the magnetic field of the ferrous material and readings from an ambient magnetic field.

16. The method of claim 1, wherein calculating the distance to the ferrous material from the plurality of magnetometers comprises calculating the distance to the ferrous material from a magnetometer of the plurality of magnetometers disposed closest to the ferrous material.

17. The method of claim 1, wherein the providing a plurality of magnetometers comprises providing at least one magnetometer with a single metallic coil.

18. The method of claim 1, wherein the providing a plurality of magnetometers comprises providing at least one fluxgate magnetometer.

19. The method of claim 1, wherein the providing a plurality of magnetometers comprises disposing the plurality of magnetometers on a printed circuit board.

20. The method of claim 1, further comprising disposing a magnetic shielding device partially around the plurality of magnetometers.