MAGNETIC DETECTION SYSTEM FOR DETECTING MOVEMENT OF AN OBJECT UTILIZING SIGNALS DERIVED FROM TWO ORTHOGONAL PICKUP COILS

• US 3,644,825 A
• Filed: 12/31/1969
• Issued: 02/22/1972
• Est. Priority Date: 12/31/1969
• Status: Expired due to Term

• Current Assignee: Halliburton Company
• Original Assignee: Paul D. Davis Jr, Thomas E. Mccullough
• Inventors: Davis, Paul D. Jr., McCullough, Thomas E.
• Primary Examiner(s): Rolinec, Rudolph V.
• Assistant Examiner(s): Corcoran, R. J.
• Application Number:
  US04/889,574
• Time in Patent Office: 783 Days
• Field of Search: 324/41,43,8,3,4 340/38L,258C,195,197 33/204,204.4,204.43
• US Class Current: 324/207.26
• CPC Class Codes: G01V 3/081 the magnetic field is produced by the objects or geological structures characterised by the method of magnetic field measurement G01R33/00
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

A pair of magnetic field sensors are disposed perpendicular to one another for sensing, at a single location, different directional components of a magnetic field. The output signals from the magnetic field sensors are vectorally combined to provide vector representations of the varying magnetic field. The direction of movement of the vector representations is then determined in order to indicate either the direction of movement of the object creating the variations in the magnetic field or the relative position of the object with respect to the sensors.

Claims

1. A system for detection of varying magnetic fields at one location, said varying magnetic fields being caused either by movement of an object through a fixed external field, or by movement of an object carrying a source of magnetic fields relative to said one location, said system comprising:

a plurality of magnetic field sensors each generating output signals representative of a different directional component at said one location of a magnetic field, means responsive to the output signals from said sensors for generating time derivative signals, and means for combining said output signals with said time derivative signals to produce resultant signals representative of the direction, speed and magnetic moment of said object causing the varying magnetic field.

2. The system of claim 1 wherein the sign of said resultant signals is dependent upon the direction of movement of the object causing the varying magnetic field.

3. The system of claim 1 wherein said field sensors generate output signals representative of perpendicular magnetic field components.

4. The system of claim 1 wherein said magnetic field sensors comprise magnetometers including means for removing steady state magnetic field components from the output thereof.

5. The system of claim 1, wherein said means for combining comprises circuitry for multiplying each said output signal by the time derivative of the other output signal.

6. The system of claim 5 and further comprising:

means for subtracting one multiplication product from the other product to generate a signal having a polarity dependent upon the direction of movement of the object.

7. A system for detection of varying magnetic fields at one location comprising:

means fOr generating a pair of output signals representative of two directional components of a varying magnetic field at said one location, means for differentiating each of said output signals, means for generating multiplication products by multiplying each said output signal by the differential of the other output signal, means for subtracting one multiplication product from the other multiplication product, and means for sensing the polarity and magnitude of the remainder of the subtraction operation.

8. The system defined in claim 7 wherein said means for generating a pair of output signals comprises a pair of coils responsive to orthogonal magnetic field components.

9. The system defined in claim 7 wherein said means for generating a pair of output signals comprises a magnetometer having coils disposed perpendicular to one another.

10. The system defined in claim 7 wherein said means for multiplying comprises a gate controlled by said means for differentiating.

11. The system defined in claim 7 wherein the varying magnetic field results from an object moving relative to said one location, said object either carrying a source of magnetic fields or passing through a fixed external field, and the polarity of said remainder of the subtraction operation is dependent upon the direction of travel of said object causing the varying magnetic field.

12. A method for detecting a varying magnetic field at one location comprising:

generating output signals representative of two directional components of a varying magnetic field at said one location, differentiating each of said output signals, generating a pair of multiplication products by multiplying each said output signal by the differential of the other output signal, subtracting said multiplication products from one another, and detecting the polarity and magnitude of the remainder of the subtraction.

13. The method of claim 12 wherein said two directional components are perpendicular.

14. The method of claim 12 wherein the varying magnetic field results from an object moving relative to said one location, said object either carrying a source of magnetic fields or passing through a fixed external field, and the polarity of the remainder of the subtraction is dependent upon the direction of travel of said object causing the varying magnetic field.

15. The method of claim 12 and further comprising:

eliminating from said output signals steady state portions resulting from the earth'"'"''"'"'s magnetic field.