Re: Backup media in stray fields
G. Pearson (gpearson@blue.weeg.uiowa.edu)
Mon, 12 Jun 1995 16:52:45 -0500
Steve Philson <philson@nmr.chem.umn.edu> wrote
> ... In your situation the people directly below will probably be working
> close to the 5G line, and you may have to have someone make measurements if
> the room is to be general access. They will certainly see distortions in
> their computer monitors, and may need to be made aware of field effects. I
> usually don't worry about having a floppy disk or a magnetic tape in a 5G
> field, but you have to be careful of other things. Steel tools and other
> objects become magnetized. The local fields from these objects may be much
> greater than the steady stray field that magnetized them, so you can create
> a whole army of harmless-looking things that can damage data if floppy
> disks or tapes are set next to them. I have never seen warnings about
> this, and would be happy to learn that my fears are groundless, if someone
> has better information. That is why I am posting this back to the ammrl
> too.
Steve, you might be interested in some parts of my answer to Charlie Fry:
> 1. _DO_ _NOT_ use desktop computers, but get everything in tower cases,
> and make sure the cases are on the floor. Since far-field dipolar field
> strength varies as inverse _CUBE_, every little bit of additional distance
> helps.
> 2. Steel filing cabinets (and presumably also other steel office furniture
> such as desks) concentrate the fields, and should be avoided. Use wood,
> plastic, etc. I had a steel filing cabinet close to the monitor of my PC
> for a while. Funkidelic monitor colors became _much_ less of a problem
> after I moved that filing cabinet.
> 3. We have several monitors at roughly 5-gauss field strength, and we
> shield them. Mild steel (1/16" sheet metal) cubes open at the front and
> back surround the monitors, with at least an inch of "breathing room" for
> ventillation top & sides. Fairly cheap to make. Arc weld or spot weld,
> then spray paint.
> Monitor screen recessed about 1 or 2 inches into the cube. Degauss
> after the monitor is in place inside its shield. You'll have to degauss
> again if you move anything. Buy a degaussing coil from some TV electronics
> supply place. Should cost maybe $30. When degaussing, move the coil
> around not only the front of the monitor, but also the sides & top.
-- Gerry
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Gerald A. Pearson INTERNET: gerald-pearson@uiowa.edu
Chem. Dept., Univ. of Iowa VOICE: 319-335-1336
Iowa City, IA 52242-1219, USA FAX: 319-335-1270
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