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    Re: RIP the [Fluxgate compass /benefits of 3 axis] ?
    From: George Huxtable
    Date: 2002 Feb 4, 14:22 +0000

    Jared Sherman said-
    
    >George, with all this talk about the uncorrectable problems inherent in
    >fluxgate compasses it seems that there is a point going unspoken.
    >
    >Perhaps if these errors are all so damaging, the fluxgate compass is an
    >obsolete artifact that should be abandoned along with the sunstone and the
    >astrolabe.
    
    ==================
    
    Reply from George-
    
    Well, let's keep a sense of proportion about all this.
    
    What I was trying to get over to members is that there is nothing magic
    about fluxgate instruments that makes them immune from the disturbances
    that affect other magnetic sensors (needle compasses).
    
    I didn't maintain that those disturbances were "uncorrectable" (I hope).
    What I tried to point out was that they could be corrected, but it needed
    several extra transducers to go with the fluxgate. Fast-responding sensors
    of tilt-change, insensitive to linear accelerations, to determine the
    short-term changes in the vessel's attitude, and slow-responding
    gravity-sensors to establish the mean values of those tilts. Those sensors
    do not need to be very expensive ones. A kit which combined a strap-down
    3-axis fluxgate with those sensors could do a good job in measuring the
    magnetic azimuth of the vessel's fore-and-aft line, with little
    perturbation from the sea conditions.
    
    Even without such electronic complications, however, a simple gimballed
    fluxgate transducer does a reasonable job in steering most craft.
    Performance gets worse as the sea gets rougher, as we all know. It gets to
    the point where an experienced helmsman can do much better, partly because
    he can see the plane of the horizon, but also because he can observe the
    waves and steer the best path amongst them. Whereas even the best
    self-steering system can only try to maintain, blindly, a constant magnetic
    course.
    
    But that experienced helmsman loses much of his advantage when it gets
    dark. A single-hander has to sleep sometimes.
    
    There is a requirement for improved magnetic steering systems, and the
    technology to do it. My hope is that for self-steering, strap-down fluxgate
    instruments, properly corrected for dynamic tilt changes, will come within
    our reach before long.
    
    But nothing is going to persuade me to leave my old Sestrel compass at home.
    
    George Huxtable.
    
    
    ------------------------------
    
    george---.u-net.com
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.
    ------------------------------
    
    
    

       
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