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    Re: Fluxgate compass /benefits of 3 axis
    From: George Huxtable
    Date: 2002 Jan 30, 4:20 PM

    Brian Whatcott's last mailing said-
    
    >> >I expect this offering from
    >> >Crossbow at San Jose will be the wave of the future:
    >> >
    >> >
    >> >[sample text]
    >> >The CXM544 sensor detects the Earth's magnetic field using a 3-axis
    >> >magnetometer. The sensor computes a continuous measure of orientation using
    >> >the 3-axis accelerometer as a gravitational reference field. The product
    >> >uses the SoftSensor� architecture to compensate for temperature drift,
    >> >alignment, and other errors. The CXM544 finds applications in old well
    >> >logging, marine systems, and magnetic compassing. ...
    >> >Download CXM544, Micro Orientation Sensor, Datasheet (PDF)
    >>
    >>A 3-axis accelerometer is a fancy sort of pendulum device.
    >...
    >>George Huxtable.
    >
    >Let me write it again for your review:
    >     A 3 axis fluxgate of this kind computes
    >        "....a continuous measure of orientation."
    >
    >This means it can sense pitch, roll, and yaw, and process the magnetic input
    >accordingly.   That's why it is the wave of the future!
    >
    >
    >Brian Whatcott
    >   Altus OK                      Eureka!
    
    ================================
    
    
    Response from George Huxtable.
    
    
    Brian Whatcott and I seem to disagree thoroughly about this question, but
    we need more information about the device in question to resolve it.
    
    All there is to go on is what the blurb states-
    
    "The CXM544 sensor detects the Earth's magnetic field using a 3-axis
    magnetometer. The sensor computes a continuous measure of orientation using
    the 3-axis accelerometer as a gravitational reference field."
    
    The phrase "using the three-axis accelerometer as a gravitational reference
    field" is presumably a fancy way of saying that it's used to determine
    which way is up. And that is presumably done by measuring the three
    components of the acceleration due to gravity. That's what an accelerometer
    does: it measures accelerations.
    
    But on a surface craft there are all sorts of random accelerations taking
    place, in unpredictable directions, of a magnitude comparable with that of
    gravity, depending on the sea state. These get hopelessly jumbled up with
    the acceleration due to gravity. Can a three-axis accelerometer somehow
    unscramble these accelerations? Brian seems confident that it can.
    
    I have severe doubts. In the past, many instruments have been "hyped" up to
    appear different, and better, than their competitors. We need to collect
    more information before we can settle the matter. Who is going to be brave
    enough to buy one of these instruments and fit it to his boat?
    
    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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