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Shielding against magnetic fields.

pierre smith

Well Known Member
We flew to the Bahamas in February and my D-100 was 40 degrees off...usually spot on so I asked the other three passengers what they had packed.

Turns out that my buddy had packed his C-Pap machine and it has a motor in it, apparently with fixed magnets in it.

After we landed and unpacked, the D-100 was spot on again.

On the return trip, we changed the location of the C-Pap and were off 20 degrees.

I wonder if wrapping it in aluminum foil would shield the interference to my magnetometer.

Any ideas/suggestions.

Thanks,
 
No, aluminum foil won't work ... you'll need something ferrous (iron based) to put it in. The performance of the shield is a function of the magnetic permeability of the material and its thickness; a stronger magnet needs more material and/or greater permeability to keep the material from magnetic saturation to keep all those magnetic field lines in the box. "mu-metal" is an excellent magnetic shield can be ordered in various configurations, but its expensive. And, heavy.

For your c-pap case, you can experiment. Try putting it in a steel box (maybe a surplus ammo can of the right size?) and see what effect it has on your system.
 
Mu-metal more like conduit than a barrier

I had to research mu-metal a bit and some of the products the company I work for use it in really sensitive RF sections. That info/those guys tell me mu-metal is more like a conduit than a energy absorbing barrier. The mu-metal provides a favorable flux path, but what magflux goes in must come out, hopefully around whatever it is you're trying to shield. This idea seems to ring true with how shielding my compass worked out. A big permanent magnet motor might require cocooning it, I don't know if that would work or not. I do know it would be $$$$ to try!
 
A lunch box maybe?

Thanks guys,

Yes, a Lunchbox like one of these.
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tumblr_mjkmlv65rG1s5y6kto1_500.jpg


:D
 
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Precision Aviation Inc. PAI-700 Recommends

My PAI-700 Magnetic Compass Compensation INFO:

"Magnetic shielding material, a nickel alloy, may be used effectively to contain the magnetic field generated by permanent magnets"

Not sure if there is a special metal they are talking about or just any nickel alloy will work.

I know that my old computers used to use some kind of chrome looking spray paint inside for shielding. It was painted onto plastic parts that was completely enclosed around the internal computer board.

Wonder if the spray cans of chrome paint might work?
 
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Well, remove the sandwich first

Pierre's metal lunchbox suggestion actually shows, in principle, what is needed. So, yes, moving the sensor to the wingtip like the big boys do will reduce any future hazard. We don't need another Bermuda triangle story.

Mu metal (a special nickel alloy) is good for shielding weak fields, but it will saturate easily under strong fields like near a permag motor. These high permeability materials are very "conductive" magnetically, but it will only carry about half the lines of force that ordinary steel will.

So, use soft steel for close in shielding of strong magnetic sources.
 
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