Post by thread:High gauss magnetic material

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 ____________________________________________________________________ More than just email--Get your FREE Netscape WebMail account today at http://home.netscape.com/netcenter/mail

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.

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: {Quote hidden}>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 > >____________________________________________________________________ >More than just email--Get your FREE Netscape WebMail account today at http://home.netscape.com/netcenter/mail > >

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