US 6,282,803 B1 · Self calibration circuit for determining an accurate zero compensation for a fluxgate compass

Abstract

A self calibrating zero compensation circuit for a fluxgate compass comprising a toroidal core; a drive winding coupled to said core, and at least one and preferably two secondary sensing windings coupled to said core comprises a continuously operating demodulator coupled to the sensing windings and an intermittently operated drive signal fed to the drive winding. A microprocessor is coupled to the demodulator output through an analog to digital converter. The microprocessor provides alternatingly to the drive winding a drive signal for a first period of time and prevents transmission of the drive signal for a second, preferably equal period of time. During the second period of time, the sensing windings and the demodulator provide an output signal to said microprocessor representing the zero signal reference. The demodulator output during the first period of time represents the magnetic field signal from the compass. The output signal during the second period of time is used by the microprocessor as a zero reference or base for processing the demodulated output signal during the first period of time to self correct for drift and internal changes within the compass sensor over time.

Claims23

Dependent claims

A self calibration method of zero compensation for a fluxgate compass, said fluxgate compass having a ferromagnetic core, a drive coil positioned around the core and at least two secondary sensing coils spaced around portions of said core, said method comprising the steps of:

generating and passing a drive signal through the drive coil for a first period of time, the drive signal selected to alternately drive the core into saturation in a first direction and drive the core into saturation in a direction opposite the first direction;
sensing a first sensor signal using at least one of the secondary sensing coils, where the first sensor signal includes a first portion sensed while the core is saturated in the first direction and a second portion sensed while the core is saturated in the opposite direction;
sensing a second sensor signal during a second period of time from at least one of said sensing coils while the drive signal is removed;
and
using said second sensor signal to determine a zero reference;
and
determining a magnitude of said first sensor signal using the first and second portions of the first signal and the zero reference.

4 more elements

A self calibrating zero compensation circuit for a compass sensor wherein the sensor comprises a ferromagnetic core, a drive coil around the core, and at least two secondary sensing coils around separate portions of said core, said circuit comprising:

an oscillator operably connected to a square wave generator;
a microprocessor to generate a drive signal coupled to said drive coil to drive said drive coil into saturation in a first direction and into saturation in a second direction opposite the first direction during a first period of time, said microprocessor capable of removing said drive signal from said drive coil during a second period of time, said microprocessor adapted to receive and use an output signal from said secondary sensing coils during said second period of time to determine a zero reference, said microprocessor capable of processing said output signal from said secondary sensing coils received during said first period of time with the zero reference;
a demodulator adapted to be connected to each of said secondary coils and operably connected to said square wave generator, said demodulator having at least one anti-phase switch capable of demodulating the output signal from said secondary sensing coils generated from the positive saturation drive signal and capable of separately demodulating the output signal from said secondary sensing coils generated from the negative saturation drive signal, said demodulator providing an output signal to said microprocessor.

Dependencies are inferred from the claim text.

Self calibration circuit for determining an accurate zero compensation for a fluxgate compass

Life of this patent

Self calibration circuit for determining an accurate zero compensation for a fluxgate compass

Life of this patent

Abstract

Claims23