question on magnetic compasses

Discussion in 'Off-Topic' started by count_volta, May 11, 2010.

  1. count_volta

    Thread Starter Active Member

    Feb 4, 2009
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    I just bought a really cool looking compass from Harbor Freight Tools. This baby. http://www.harborfreight.com/sundial-compass-96734.html

    It looks really nice, like something from the 19th century. Even says West London on it. But there is a small problem.

    I tried the compass and its very inaccurate. It points in different directions, and I tried it in a spot where I know the real direction of North, and it pointed in every direction on earth but North. What gives?

    I used a magnet to test it and it reacts to the magnet just like a compass is supposed to. So why doesn't it work? I know its cheap, but so what? In theory you can make a compass from a cork with a magnetized needle in a bowl of water and it will point north. This device is supposedly made to be a little more accurate than the bowl of water, and yet it doesn't work.

    Has anyone else bought this compass, or has any idea why it wouldn't work? I already started thinking that heck it might be all the insane amounts of electromagnetic waves surrounding us in the modern world and interferring, but that can't be the reason why.
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    The needle may have either been poorly magnetized or the magnetic field has been retarded by close proximity to stronger fields.

    If you can open the top, you can drag your magnet from tip to tip a few strokes, always in the same direction and re-magnetize the pointer.

    And WOW, thats a beauty for $10! Im going to have to buy one.
     
  3. count_volta

    Thread Starter Active Member

    Feb 4, 2009
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    Ah so maybe when I was testing it with my magnet (pretty powerful magnet), that may have messed up the needle. Hmmm. I will see if I can open it.

    Btw this is my new favorite store ever!!! I bought this very nice multimeter there. http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html

    I tested it and its very accurate for such a low price. Its no Fluke, but still very accurate. At least it gave me the same results I got with my lab multimeter in college.
     
    Last edited: May 11, 2010
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    Quite (most) likely. Its an easy fix, especially it isnt a liquid filled compass.
     
  5. count_volta

    Thread Starter Active Member

    Feb 4, 2009
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    Do I really have to open it to do this? I can open the cover with the sundial you see there in the picture, but it has another glass cover over it. Can I do it through the glass?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    no.
    You have to keep the needle still and rub the magnet over it in the SAME direction a few times.

    Preferably touching the magnet to the needle.

    If the needle is flailing all around, you are not lining up the magnetic moments properly. they need to be lined up for the compass to work.
     
  7. bundick

    Active Member

    Dec 19, 2007
    97
    1
    Practice that 'rubbing' on a flat piece of steel before you tackle your pretty sundial.
     
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