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Subject: Re: Fluxgate compass
From: Lu Abel (lunav@XXX.XXX)
Date: Tue Jan 29 2002 - 12:58:27 EST
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).
Lu
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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