Where to scavenge mu-metal?



http://www.germes - online.com/direct/dbimage/50068769/Power_Supply_Transformer.
Not necessary to ground it?
Is wider (as wide as the windings) best? Dimension confusion...
Thanks,
--
Sparky


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wrote:

Not if your problem is magnetic field leakage.

Think of it as a single, shorted secondary turn but *outside* the laminations. Any field that leaks out of the transformer induces a current into the strap, and it in turn generates a field that fights the excitation. It should be thick, wide, and well-shorted, which means well soldered. Copper is best.
John
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No need to ground, I presume...
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Gave us:

Have you formed the leads going to your project into twisted pair yet? I guarantee that will reduce injected noise a LOT.
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http://www.germes-online.com/direct/dbimage/50068769/Power_Supply_Transformer.jpg
That transformer in the picture is a ferrite cored one from a switch-mode power supply, and is designed to run at a frequency of around 100kHz. A copper band around such a tranny, is a whole different kettle of fish to putting one around a low frequency power transformer. Some such trannies have a copper shield right around the windings, inside the lamination limbs, but if I recall correctly, this is more for electrostatic shielding purposes, than magnetic. The first thing I would try, before getting all complicated with mumetal shields, is to rotate the tranny through 90 degrees in the horizontal, and if that doesn't work, doing the same in the vertical, or any combination. I've found that this will often reduce or even eliminate stray field pickup by adjacent circuitry. The tranny mounting holes may even still line up in the best case, but even worst case, it's only a case of drill 4 more, or make up a right-angle bracket.
Arfa
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Gave us:

Make sure you simply twist your output lines from the banana jacks, right up to the circuit under test. Your noise figure should drop a lot on that act alone. A couple turns per inch... not too damn loose or it does no good.
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You might try your local recycling center to see where thay tear down old CRT monitors and TV's. Maybe if they let you come by you can spot some.
SparkyGuy wrote:

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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Isn't moo metal what they make cow magnets from!
SparkyGuy wrote:

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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I used to think so, but when I went to college, I learned that it's made from cats!
Tim
-- "Librarians are hiding something." - Steven Colbert Website @ http://webpages.charter.net/dawill/tmoranwms

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SparkyGuy wrote:

As soon as you cut it or otherwise stress it, mu metal becomes worthless.
--
Many thanks,

Don Lancaster voice phone: (928)428-4073
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wrote:

High MU metal is not a particularly rare material. I assume you are attempting to shield something from a low frequency magnetic field. You may find the cast-iron door of an old stove or wood furnace will be all you need.
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Now *there's* a mental picture that deserves framing!
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Don Lancaster wrote:

That is a completely garbage overstatement. Just the same, any tight bend (bending r less than 10 thicknesses) will require annealing in a reducing atmosphere. It is really quite intolerant of cold working if you wish to maintain the magnetic properties. Do not even flex it unnecessarily.
--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
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