US 5,297,065 AGranted

Magnetic transient detection and calibration technique for an auto-calibrating compass

AssigneeChrysler Corporation

InventorsRussell E. Cage, John A. Wilke, Rafi A. Al-Attar

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Abstract

A magnetic transient detection technique which alerts a microcomputer of an auto-calibrating compass when electrical transients which produce magnetic transients have occurred. The technique employs an electronic compass control circuit having a sampling rate high enough to isolate electrical transients from transients produced by normal motion of the vehicle. Accelerations in data values defined as the difference between two changes in the coordinates for the center of the earth's magnetic field circle, are calculated and compared to predetermined threshold accelerations. Previous acceleration values and their associated vehicle magnetic field vectors can be stored in the microcomputer. After a magnetic transient is detected, its associated vehicle magnetic field vector is subtracted from the resultant magnetic field to yield vehicle heading. Once detected, magnetic transients are also used to initiate auto-calibration.

Claims5

Dependent claims

In an electronic compass system for a vehicle operating within a resultant magnetic field made up of the earth's and vehicle's magnetic field wherein said vehicle's magnetic field periodically includes electrical transients, a technique for calculating heating comprising:

(a) orienting first and second sense coils of a flux-gate sensor perpendicular to each other in the earth's magnetic field;
(b) saturating said sense coils with a drive signal;
(c) measuring an induced voltage in said sense coils induced by said resultant magnetic field;
(d) sensing, calculating and storing in a memory unit of a processing unit a first heading data value related to said induced voltage for a resultant magnetic field for a given vehicle heating;
(e) sensing, calculating and storing a second heading data value related to said induced voltage for the resultant magnetic field for said given vehicle heating;
(f) calculating and storing a first heading data velocity by subtracting said first stored data value from said second stored data value;
(g) sensing and storing a third heading data value related to said induced voltage for the resultant magnetic field for said given vehicle heading;
(h) calculating and storing a second heading data velocity by subtracting said second stored data value from said third stored data value;
(i) calculating and storing a heading data acceleration by subtracting said first stored data velocity from said second stored data velocity;
and
(j) comparing said heading data acceleration with a predetermined data acceleration representing the minimum acceleration caused by electrical transients;
(k) calculating and storing a vehicle magnetic field vector;
(l) calculating and storing a vector change in said vehicle magnetic field vector when the heading data acceleration exceeds said predetermined heading data acceleration;
(m) calculating a new vehicle magnetic field vector by adding said stored vector change to said stored vehicle magnetic field vector;
(n) recalling calibration values associated with said stored vehicle magnetic field vector when said new vehicle magnetic field vector corresponds to said stored vehicle magnetic field vector;
(o) adding said calibration values to said new vehicle magnetic field vector;
and
(p) making said new vehicle magnetic field vector available for communicating heading information to a vehicle user.

15 more elements

An electronic compass control circuit comprising:

(a) a flux-gate having two sense coils and a primary coil;
(b) a flux-gate drive coupled to said primary coil for periodically saturating the flux-gate;
(c) a multiplexer having at least first and second inputs coupled independently to said two sense coils of the flux-gate;
(d) a bandpass filter coupled to said multiplexer;
(e) a first synchronous detector coupled to said bandpass filter for detecting a first filtered signal from one sensed coil of said flux-gate;
(f) a second synchronous detector coupled to said bandpass filter for detecting a second filtered signal from the other sense coil of said flux-gate;
(g) a first integrator coupled to said first synchronous detector for producing a first direct voltage containing heading information;
(h) a second integrator coupled to said second synchronous detector for producing a second direct voltage output containing heading information;
(i) an analog-to-digital converter coupled to the output of said first and second integrators for converting said first and second direct voltage outputs into digital codes;
and
(j) a microcomputer coupled to said analog-to-digital converter for controlling said flux-gate driver, said multiplexer, and said synchronous detector, and for determining compass headings as a function of said digital codes, the rate of change of said digital codes and the rate of change of the rate of change of said digital codes;
said first direct voltage output remaining constant while said second integrator is producing said second direct voltage output and said second direct voltage output remaining constant while said first integrator is producing said first direct voltage output.

9 more elements

Dependencies are inferred from the claim text.