Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Fluxgate compass
    From: Lu Abel
    Date: 2002 Feb 1, 13:16 -0800

    At 09:29 AM 1/30/2002 -0500, Chuck Griffiths wrote:
     >   But, how does making constant rate turns help the fluxgate find
     > magnetic north if it sensed it incorrectly [didn't read 0 degrees when
     > boat was heading 000M] to begin with?  
    If one plots deviation as a function of compass direction it should look
    like a sine wave (for fiberglass and wood boats at least, not sure about
    steel).  If the sine wave is "off center" (ie, the plot shows more westerly
    deviation that easterly or vice versa) it is an indication that the lubber
    line of the compass is not aligned with the ships keel.
    After I learned this fact I plotted the deviation table for my 36' sailboat
    and -surprise- it was uneven.  Even though it's a high quality boat, the
    compass had been fastened to the steering pedestal with the lubber line of
    the compass pointing about 2 degrees to starboard.  Hard to discover, easy
    to fix once I had done so.
    What I suspect that any decent deviation-determining software does is
    simply to even out the deviation readings so the sine-wave is "balanced."
    >Now, I can imagine that after the compensating program is run, the fluxgate
    >could compare the rate of turn indicated during the compensating turns and
    >adjust indicated headings such that they match headings as they should have
    >appeared during the turns. To continue my example, the fluxgate could
    >sense the
    >rate of turn and know that 90 degrees of turn have been completed so the
    >should indicate east, the previous error between 80 and 90 degrees could be
    >corrected. Of course, I checked
    >it after I corrected it by comparing headings to sun bearings so I know it
    >works, I'm just wondering if someone can explain how it works.
    >____________________Reply Separator____________________
    >Subject:    Re: Fluxgate compass
    >Author: Brian Whatcott 
    >Date:       1/29/02 6:33 PM
    >At 05:16 PM 1/29/02, you wrote:
    > >... 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. ...
    > >George Huxtable.
    >George, the comments I posted were on the basis of examining the
    >constructional details of a fluxgate.   In view of your praiseworthy
    >efforts in describing the Lunar, I'll try to return the favor by taking
    >   a look at what the commercial fluxgate offerings provide.
    >It may be that for a 2-axis fluxgate, a pendulous mount might be adopted.
    >This would retain the pendulous errors associated with a compass card
    >   of the conventional kind. I'll get back to the list, if I find useful
    >engineering input.
    >A three axis fluxgate can be mounted rigidly. This is sometimes called a
    >'bolt-down' sensor.
    >This e-mail and any files transmitted with it are confidential and may
    >be legally privileged or otherwise exempt from disclosure under
    >applicable law. This e-mail and its files are intended solely for
    >the individual or entity to whom they are addressed and their content
    >is the property of Smiths Aerospace.  If you are not the intended
    >recipient, please do not read, copy, use or disclose this communication.
    >If you have received this e-mail in error please notify the e-mail
    >administrator at postmaster@si.com and then delete this e-mail, its
    >files and any copies.
    >This footnote also confirms that this e-mail message has been scanned
    >for the presence of known computer viruses.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site