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    Re: Fluxgate compass
    From: George Huxtable
    Date: 2002 Jan 29, 4:17 PM

    Brian Whatcott said, about fluxgate compasses-
    >There are some compass errors associated with the physical interaction
    >between a tiltable compass card, and a tilted geomagnetic field, such as
    >acceleration and turning (properly rolling) errors. These are abolished
    >with a bolt down sensor.
    Response from George Huxtable
    I would like to understand what Brian is saying a bit better. What exactly
    is a bolt-down sensor? And what errors does it "abolish"?
    As I understand it, a fluxgate compass, like any other compass, needs to
    establish the direction of the horizontal component of the Earth's field,
    with respect to the direction of the vessel. For this to happen, somehow
    the fluxgate compass, just like any other compass, has to be aware of the
    direction of the horizontal. In a magnetic compass, this is achieved by the
    gimballing, and by the needle pivot which allows the card to remain roughly
    horizontal under all conditions of tilt of the vessel.
    Doesn't the fluxgate-component within a fluxgate instrument need to be kept
    horizontal by gimballing in just the same way, even if that part of the
    works is concealed within a bolted-down box? Has a fluxgate system been
    invented that needs no internal gimballing?
    If a fluxgate were bolted down with no such gimballing, wouldn't it have to
    assume that the deck of the vessel always maintained a horizontal attitude?
    That would be an absurd assumption for a sailing vessel, and a doubtful one
    for a powered craft in rough weather.
    Perhaps someone can explain further.
    George Huxtable.
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.

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