Compass fluxgate

The principle of a Magnétomètre fluxgate is to measure the Projection Terrestrial magnetic field on an axis, thanks to a magnetic material presenting a “Saturation”. One adds to the measured component of the Terrestrial magnetic field, a alternate Magnetic field, created by a sinusoidal current which traverses a reel (a Solénoïde). The terrestrial field behaves a little as if one superimposed on the running Sinusoïdal a D.C. current. There is thus an imbalance between the passage to the Saturation when the terrestrial field “helps” the exiting field, and the opposite passage where the terrestrial field “opposes” the exiting field. This imbalance is measured, by an electronic method , and gives a measurement of the value of the Projection of the terrestrial field.

To have the direction (Azimuth) of the terrestrial field, it is advisable to have two devices fluxgate whose axes are directed with 90° one of the other. One thus measures the Projection S of the terrestrial field on two axes Perpendiculaire S, and a simple calculation of Trigonométrie (a “arctangente”) makes it possible to calculate the Azimut. The advantage compared to a traditional magnetic compass is that one frees oneself from the slope of the magnetic field compared to the vertical. They is also very precise and insensitive with the Accélération S create by the movements of a Bateau. For a Autopilot, it is thus the ideal.

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