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PICList Thread
'High gauss magnetic material'
1998\11\17@234109 by STEVE TOMES

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Picsters....

     I am curently working with high gauss miniature magnets.....
     I know that they can destroy a hard drive and floppy disk..but how      
do they effect a pic...and eprom????  Can they be shielded as you       would
shild an RF design??  Also would they create a problem in       close
proximity to a Switcher type circuit?
            Thanks for any input..STEVE TOMES

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1998\11\18@001618 by Dave VanHorn

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STEVE TOMES wrote:
>
> Picsters....
>
>       I am curently working with high gauss miniature magnets.....
>       I know that they can destroy a hard drive and floppy disk..but how
> do they effect a pic...and eprom????  Can they be shielded as you       would
> shild an RF design??  Also would they create a problem in       close
> proximity to a Switcher type circuit?

Yes.

Too many questions in too many directions.
They can't affect a pic, it's memory is stored differently. Eprom is
same.
You can shield magnetic fields, although what you really do is more akin
to shorting them out rather than reflecting or absorbing. Mu-Metal is
used here, because it provides an excellent path for flux lines to
complete through.

They can kill a switcher, or help it operate(!)  If you saturate a
switcher's core with the magnet, it will fail, usually catastrophically.
However, you can use a magnet to bias a switcher's inductor in the
opposite direction to the current flux, and double the power handling
capability of a given inductor at a given frequency.

1998\11\18@043316 by Joe McCauley

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Steve,

There is a material called Mu metal which is a magnetic shield material. I
think it is used on the outside of oscilloscope tubes. I have no idea where
to get it from (or even if I have spelled the Mu part correctly) so this
info may be not so useful. Prehaps someone else knows what I am talking
about. If anyone has any info on this I'd also like to know.

I don't believe the magnets will affect a PIC or E2PROM (unless they are
moving quite close to the circuit, in which case you might induce some
voltages in the circuit) I work with such magnets a lot and have never had
any trouble. I have built a system using several PICs and a DS5000 talking
to a PC to control a 25 Tesla pulsed field system. The only effect I see
from the field pulse ( at a distance of 1.5M) is distortion of the picture
on the monitor when the field is triggered.

As to the switcher circuit is it an SMPS? If so it is in theory possible
that your magnets
could partially saturate the core of the transformer. I imagine this could
cause problebs, but I am not a switching power supply expert.

Hope this helps,

Joe

At 23:40 17/11/98 EST, you wrote:
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1998\11\18@120634 by Peter L. Peres

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On Tue, 17 Nov 1998, STEVE TOMES wrote:

>       I am curently working with high gauss miniature magnets.....
>       I know that they can destroy a hard drive and floppy disk..but how
> do they effect a pic...and eprom????  Can they be shielded as you       would
> shild an RF design??  Also would they create a problem in       close
> proximity to a Switcher type circuit?

A sufficiently high gauss magnet can induce enough voltage in a simple
wire to disturb attached circuits, if it moves fast enough against it (for
example while flying towards a magnetic metal part on an operating P.C.B.

The newer magnets are capable to generate voltages in excess of 1V when
moved by hand over a single conductor (use a scope as read-out and a sheet
of transparency to put the wire under, and slide the magnet over).

Strong magnets can move a loaded ferrite core into saturation and reduce
or upset switchers but this requires quite close proximity.

Shielding static magnetic fields completely is hopeless, but they can be
reduced to amounts tolerable by equipment using a set of shields to form
a magnetic circuit (and essentially move a high-field gap away from
equipment).

Peter

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