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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics,rec.ham-radio
Subject: Re: Flux Gate Compass
Summary: A few comments...
Keywords: Direction, Flux Gate, Compass
Message-ID: <4346@kitty.UUCP>
Date: 24 Jan 91 16:07:40 GMT
References: <541@cow.ecs.oz>
Organization: Recognition Research Corp., Clarence, NY
Lines: 47

In article <541@cow.ecs.oz>, bmp@cow.ecs.oz (Bruce Paterson) writes:
> A friend is attempting to build (from scratch) a flux-gate compass
> for use in a vehicle mounted dead-reckoning navigation system. 

	You might have a difficult time in the design and winding of the
flux gate itself, which is not a trivial undertaking if you hope to achieve
any reasonable accuracy and linearity!  While there are single-phase
rectilinear flux gates wound on a straight core, it is more common to see
two-phase and three-phase flux gates wound on toroidal cores.  I cannot
give you any practicable details for winding your own flux gate, however.

> We can't really use other methods of navigation like Omega or Nav-Star
> since 1) Neither are very well covered here
>       2) We need information about the current heading of the vehicle as well.

	You should be aware that even the best quality military grade
flux gates (commonly called a "north seeker", btw) have an accuracy of
no better than +/- 1 degree of azimuth, with lesser quality military
grade models having accuracies of +/- 3 degrees of azimuth.  Commercial
devices degrade from there... :-)  I point this out because some people
incorrectly believe that flux gate devices have greater accuracy than
the above.

> Has anyone had experience with these beasts ? Likely problems/ shortcomings
> etc.
> In particular
> 	1) How do you negate the magnetic effects of the vehicle itself ?
> 	   (bearing in mind we have overhead tram lines here !)

	Using small adjustable compensation magnets, which are internal to
some flux gate devices.  A traditional marine approach is to use the
large ferrous mass of a binnacle, but that is not to practicable for
a car. :-)

> 	2) How do you negate the effects of vehicle tilt (That is, the
> 	   verticle component of magnetic field biassing the readings ?

	Many military and commercial aircraft flux gates are mounted on
gimbals to provide pitch and roll tolerance of up to 45 degrees.

	For further information on flux gate devices, you might wish
to try a flux gate manufacturer, such as Humphrey, Inc. or Sperry
Navigation Systems.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231       {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635   [note: ub=acsu.buffalo.edu] uunet!/      \aerion!larry