System for ascertaining magnetic field direction

• US 4,267,640 A
• Filed: 04/30/1979
• Issued: 05/19/1981
• Est. Priority Date: 04/30/1979
• Status: Expired due to Term

• Current Assignee: General Dynamics Defense Systems Incorporated (General Dynamics Corporation)
• Original Assignee: RCA Corporation
• Inventors: Wu, Chin T.
• Primary Examiner(s): Martin, Jr., William D.
• Application Number:
  US06/034,743
• Time in Patent Office: 750 Days
• Field of Search: 33/361, 33/362, 324/244, 324/247, 324/260, 324/263, 324/253
• US Class Current: 33/361
• CPC Class Codes: G01C 17/30 Earth-inductor compasses
• CPC Class Codes: G01R 33/04 using the flux-gate principle

Abstract

A system for detecting magnetic field direction comprising a pair of orthogonally positioned rods each having a rectangular shaped BH curve, a switching winding, and detectors for detecting the switching of magnetic polarity of each rod to either of its remanent states. A switching current having a triangularly shaped waveform is supplied through said switching windings to drive said rods between their remanent states at times depending upon their angular relationship with the external magnetic field. Counters record the difference in time, measured from the immediately preceding zero current crossover points between the switching of each rod first to one of its remanent states and then to the other of said states. The time difference in one rod is proportional to the sine of the angle between the external field and said one rod and to the cosine of the angle between the external field and the other said other rod. The arc tangent of the ratio of the sine function to the cosine function is the angular relation of the external field to the rods.

Claims

1. Magnetic field direction indicating means comprising:

first and second orthogonally positioned rods, each having a rectangularly shaped BH curve and a switching winding wound therearound;

sensing means for individually sensing a change in polarity of magnetization of said rods;

second means for supplying an alternating current having a triangularly shaped waveform through said switching windings to switch the polarity of magnetization of said rods between their upper and lower levels; and

third means for determining the arc tangent of the ratio of the differences in positive and negative currents required to switch each of said rods between its upper and lower levels.

2. Magnetic field direction finding means as in claim 1 in which said third means comprises:

first time measuring means for determining a first time difference between the time intervals required to shift said first rod to its upper level and to its lower level measured from the immediately preceding zero current crossover points of said alternating current;

second time measuring means for determining a second time difference between the time intervals required to shift said second rod to its upper level and to its lower level measured from the immediately preceding zero current crossover points of said alternating current; and

calculating means for determining the arc tangent of the ratio of said first time difference to said second time difference.

3. Magnetic field direction indicating means as in claim 1 in which said third means comprises:

first logic means comprising first counter means responsive to the magnitude of the positive current required to switch said first rod to its upper level to register a first count proportional to said positive magnitude, and further responsive to the magnitude of the negative current required to switch said first rod to its lower level to register a second count proportional thereto, and further comprising means for producing a first resultant count equal to the difference between said first and second counts;

second logic means comprising second counting means responsive to the magnitude of the positive current required to switch said second rod to its upper level to register a third count proportional to said positive magnitude, and further responsive to the magnitude of the negative current required to switch said second rod to its lower level to register a fourth count proportional to said negative magnitude, and further comprising means for producing a second resultant count equal to the difference of said third and fourth counts; and

means for determining the arc tangent of the ratio of said first resultant count to said second resultant count.

4. Magnetic field direction indicating means as in claim 1 in which said sensing means comprises first and second sensing windings wound one each on said first and second rods to sense a change of magnetization from either level to the other level of each rod.

5. Magnetic field direction indicating means comprising:

a pair of orthogonally positioned rods each having a rectangularly shaped BH curve and a switching winding wound therearound;

sensing means for individually sensing a change in polarity of magnetization of said rods;

means for supplying an alternating current waveform through said switching windings to switch the polarity of magnetization of said rods between their upper and lower levels; and

means for determining the ratio of the differences in positive and negative currents required to switch each of said rods between its upper and lower levels.

6. Magnetic field direction indicating means as in claim 5 in which said means for determining the ratio comprises:

first logic means comprising first counter means responsive to a first magnitude of the positive current required to switch said first rod to its upper level to register a first count having a known relationship to said first magnitude of positive current, and further responsive to a first magnitude of the negative current required to switch said first rod to its lower level to register a second count having a known relationship to said first magnitude of negative currents, and further comprising means for producing a first resultant quantity proportional to the difference between said first magnitudes of positive and negative currents;

second logic means comprising second counting means responsive to a second magnitude of the positive current required to switch said second rod to its upper level to register a third count having a known relationship to a second magnitude of positive current, and further responsive to a second magnitude of the negative current required to switch said second rod to its lower level to register a fourth count having a known relationship to said second magnitude of negative current, and further comprising means for producing a second resultant quantity proportional to the difference between said third and fourth second magnitudes of positive and negative currents; and

means for determining the arc tangent of the ratio of said first resultant quantity to said second resultant quantity.

7. Magnetic field direction indicating means as in claim 5 in which said sensing means comprises first and second sensing windings wound one each on said pair of rods to sense a change of magnetization from either level to the other level of each rod.

8. Means for detecting the direction of a given magnetic field comprising:

first and second rods having rectangularly shaped BH curves and positioned at right angles to each other;

first and second driving windings joined together at first ends thereof and wound around said first and second rods, respectively;

first and second sensing windings wound around said first and second rods, respectively;

means for supplying an alternating current through said first and second windings to switch the magnetization of said rods to their first level during the positive portion of said current and to switch the magnetization of said rods to their lower level during the negative portion of said current;

means for measuring the difference in current magnitudes, measured from the immediately preceding zero voltage crossover points, to shift the magnetization of each of said first and second rods from its upper to its lower level and then back to its upper level again; and

comparing means for comparing the magnitudes of the current differences of each rod to determine the angular relationship between the said given magnetic field and the direction of a selected one of said rods.

9. A system for ascertaining the direction of a particular magnetic field comprising:

first and second orthogonally positioned magnetic rods located in said field, each rod capable of assuming two remanent magnetization states;

means responsive to a common alternating drive current for individually applying to each rod an alternating magnetic field for switching the respective rods between their remanent states;

sensing means for individually sensing the switching between remanent states of each rod;

means for indicating each passage of said common drive current through zero;

means for measuring the time intervals Δ

t₁ and Δ

t₂ between an indication that the drive current has passed through zero in one sense and the respective times t₁ and t₂ that the first and second rods switch to one of their remanent states, and the time intervals Δ

t₃ and Δ

t₄ between an indication that the drive current has passed through zero in the opposite sense and the respective times t₃ and t₄ that the second and first rods switch to their other remanent state, this time difference being indicative of the direction of said particular magnetic field.

10. Magnetic field direction indicating means comprising:

a pair of orthogonally positioned rods each having a rectangularly shaped BH curve and a switching winding wound therearound;

sensing means for individually sensing a change in polarity of magnetization of said rods;

means for supplying an alternating current waveform through said switching windings to switch the polarity of magnetization of said rods between their upper and lower levels; and

means for determining the ratio of the difference in positive and negative currents required to switch each of said rods from its lower level to its upper level.