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Magnet measurement

Discussion in 'Electronic Basics' started by Ken O, May 31, 2006.

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  1. Ken O

    Ken O Guest

    Hi,

    Anyonw knows the best way to measure a magnet strenght? either permament or
    electromagnet.
    would it be with a galvanometer or is there anything else on the market.
    thanks

    Ken
     
  2. Zak

    Zak Guest

    Nuclear magnetic resonance is very accurate I think...


    Thomas
     
  3. John Fields

    John Fields Guest

     
  4. Ken O

    Ken O Guest

    ya thats what i figured,
    I am thinking of building one, I found this site
    http://my.execpc.com/~rhoadley/magmeter.htm

    I am finding out that hall effect sensors are very hard to find... its not a
    hot item.


    kenO
     
  5. Chris

    Chris Guest

    Hi, Ken-O. The reason you're having trouble finding the part is that
    Radio Shack really doesn't carry very much in the way of components
    these days, and also that the manufacturer is obsoleting the part.

    The cross-reference is the Allegro A1321LUA-T. It operates on the same
    voltages, same pinout, and has the same sensitivity (5mV/G). It's
    available in stock at Digi-Key for $1.45 USD. And it has a working
    temperature range from -40C to 150C, so it can be just about as hot an
    item as you please.

    http://www.allegromicro.com/datafile/1321.pdf
    http://www.allegromicro.com/datafile/3515.pdf

    Hope that helps. Book 'em.

    Good luck
    Chris
     
  6. Guest

    Ken, generally it's measure using a Gauss meter. Modern instrument
    uses Hall Effect semiconductors for the purposes.

    Harry C.
     
  7. Ken O

    Ken O Guest

    ya , gauss meter at 500$, a little too steap for me. I thought of building
    one.
    looking into it

    ken
     
  8. Ken O

    Ken O Guest


    thats exactly it, thanks a lot,
    i did go on digikey website, I put hallsensor as a search keyword, and it
    showed me the another ' apply filter page' i was never successful to get
    those parts..
    ken
     
  9. Jamie

    Jamie Guest

    go there.
    your looking at a Gauss meter.
    http://www.trifield.com/
    http://www.trifield.com/gauss_meter.htm

    in short, you can use Webers (Wb) as the
    unit to measure with and that is.
    1 weber = the magnetic flux that produces an
    electromotive force of 1 volt in a 1 turn loop
    circuit as the flux changes from max to 0 in
    one second time.
     
  10. Don Taylor

    Don Taylor Guest

    You didn't say how accurate you needed the measurement to be.
    If you don't need terrific accuracy and you like cheap...

    How about using a compass? Put the magnet far away from your compass
    and let the compass settle down.

    Then bring the magnet closer but keep the magnet's field at right
    angles to the direction your compass is pointing. Bring it close
    enough that you see the compass needle deflect 45 degrees. At that
    point you know that at that distance the field from your magnet is
    approximately equal to the earth's magnetic field at your location.
    (You can get values for the strength of the earth's magnetic field
    near you from library references, or probably google, it seems to
    have everything else)

    This is lots cheaper than buying a gaussmeter, probably quicker to
    get you an answer too. And it is easy to get an estimated value.
    (but this trick isn't going to work for AC driven magnetic coils)
     
  11. Stumpy

    Stumpy Guest

    http://www.cy-sensors.com/Hall-IC.htm
     
  12. Chris

    Chris Guest

    OK, Ken. Just for reference, if you're having trouble finding a
    semiconductor, the first thing to do is go to the manufacturer's
    website, and punch in the part number. Sometimes you get really bad
    news, but sometimes you get some help. If you'd waited another year to
    do the project, the part would have been gone, and the recommended
    cross might not have been so easily found.

    Worse comes to worst, you can always email or call the manufacturer's
    sales engineers. They will recommend a cross (and frequently recommend
    competitors' parts.

    Good luck with your project -- it looks pretty straightforward. Feel
    free to post again if you get hung up.

    Cheers
    Chris
     
  13. Guest




    Really cheap Hall sensors (but SMT package):

    Linear Hall sensor, two for $1.00
    http://www.allelectronics.com/cgi-bin/item/SS-19T/search/HALL-EFFECT_MAGNETIC_POSITION_SENSOR_.html



    Here's my list of more. (Old list, so those available from surplus
    companies have changed.)

    http://www.amasci.com/maglev/hall.html



    For measuring less than a Gauss, here's an interesting circuit:

    Sensitive geomagnetic detector

    http://www.geocities.com/CapeCanaveral/Lab/5185/circuit1.html#SENSITIVE

    ((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
    William J. Beaty Research Engineer
    UW Chem Dept, Bagley Hall RM74
    Box 351700, Seattle, WA 98195-1700
    ph425-222-5066 http//staff.washington.edu/wbeaty/
     
  14. Jasen Betts

    Jasen Betts Guest

    you could try Hall effect ?
    a lump of iron and a strain gague?

    "best way" really depends on the expected strength
    a micrometer is great for measuring he thickness of a pcb but not much
    use mountains.


    Bye.
    Jasen
     
  15. Ken O

    Ken O Guest

    Actually I want to do different typr of coils, i need something to compare
    strenght. So i do not really need the absolute value, but just an
    indication what works best.

    ken
     
  16. Mike

    Mike Guest

    I have quit doing it now but, I have been building a little Guass
    meter for several years that slotcar (remember those?) racers use to
    test and match the little magnets in their motors. Yeah, a lot of
    those guys are very serious about their racing. Anyway, I was able to
    wholesale it for $150 so you should have no problem building one
    yourself on the cheap. The units I made used a ratiometric sensor
    similar to the ones that have been recommended. My earliest versions
    used opamps to shift and scale the sensor output that fed a panel
    meter module. The last ones I made used a sigma delta A/D and a PIC
    driving a standard LCD. Either works just fine. All have used the same
    sensor built into a traverse probe. The sensor cost me about $13 ea
    and were never in stock so I always ordered 25 at a time. Whatever
    sensor you use, make sure it stays linear throughout the range of the
    field you expect to encounter. Most of those sensors will run out at
    anywhere from +- 100-2500 Gauss. I don't know if repeatability is all
    that important to you, but keep an eye on the temperature specs for
    sensitivity, offset, and linearity.

    Mike
     
  17. Jasen Betts

    Jasen Betts Guest

    use some sort of bridge, or balance, then.
     

  18. If by "strength" you mean "lifting strength", then field strength
    doesn't necessarily tell you everything. A solenoid can have a strong
    field, but it picks up nothing. The core is important.

    The best way is probably an empirical one. Put a block of steel on a
    scale and note its weight. Attach your magnet to it and lift up.
    Watch closely and see what the scale reads just as the magnet breaks
    loose. Subtract this number from the initial weight and this is how
    much the magnet was lifting. Note that you may get a different amount
    of lift using the side of a magnet than using the end, too.

    Hope this helps.

    Don
    Kansas City
     
  19. ian field

    ian field Guest

    There's a couple of folders of datasheets at these links.

    http://www.allegromicro.com/datafile/archive/
     
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