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    Re: Fluxgate compass
    From: Lu Abel
    Date: 2002 Jan 29, 10:58 AM

    It is true that most newer fluxgate units (really the electronics and not
    the compass sensor itself) will automatically generate a deviation
    table.  One does two or three constant speed 360 degree turns and the unit
    compares (pretty exactly) the readings it sees throughout the circle versus
    the assumption that true magnetic direction is changing at a uniform rate
    during the turns.
    I took Craig's question differently, however:  Before even starting to
    develop a deviation table for a compass, a good compass adjustor first
    tries to minimize the compass's deviation though use of the compensating
    magnets within the compass and even external devices such as quadrential
    balls and Flinders sticks (the latter two are used mostly on steel vessels
    since, as one might imagine, it's quite difficult to get a compass to read
    correctly when surrounded by a big lump of iron).  Is this sort of
    compensation also done for fluxgate compasses?  Is it the same as or
    different from the way it is done for traditional compasses?
    As a practicing electrical engineer, my first guess would be that they
    would be done the same.  But I also realize that fluxgate compasses work
    quite differently than conventional compasses -- internally, they have two
    sensors and compare the fore-and-aft component of the earth's magnetic
    field to the athwartships component to determine magnetic direction rather
    than actually swinging a magnetized needle.  This might require different
    compensating practices (especially on a steel vessel).
    At 10:34 PM 1/28/2002 -0500, Rodney Myrvaagnes wrote:
    >The most recent mounted fluxgate compasses will adjust themselves if you
    >make a circle at constant speed, I am told. The old Sailcomp which came on our
    >boat and was destroyed by lightning did not, but it was 1989 or earlier.
    >On Mon, 28 Jan 2002 19:38:50 -0500, Craig wrote:
    > >In referring to Bowditch chapter 6 concerning compass adjustment, I would
    > >like to know if this applies to electronic fluxgate compasses.  Does anyone
    > >here have any experience with this or could refer me to other references?
    > >
    > >Thank you,
    > >
    > >Craig
    >Rodney Myrvaagnes                   J36 Gjo/a
    >"Win98 ate my sig block."

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