Re: Bulk erase methods

On Wed, 13 Jul 2005 16:57:58 +0000, Guy Macon wrote:

>
>
>
> Naveed wrote:
>>
>>"Guy Macon" <_see.web.page_@xxxxxxxxxxxxxxxxxx> wrote...
>>>
>>> Barry Lennox wrote:
>>> >
>>> >On 11 Jul 2005 15:45:50 -0700, bigcat@xxxxxxxxxxx wrote:
>>> >
>>> >>What methods can be used to bulk erase a lot of floppies? I dont have
>>> >>one of those nice big electromagnets, and was wondering if anything
>>> >>else to hand could be used. I presume 2 seconds in a microwave with a
>>> >>load to prevent sparking is too risky, though I should try one.
>>> >>
>>> >>Cant think of anything else that causes a strong enough mag field...
>>> >>any ideas?
>>> >
>>> >Old magnetron magnets will do the job very nicely.
>>>
>>> Magnets do indeed destroy data, but if that's all he wants to do
>>> a bonfire is even better. If he wants to re-use the floppies he
>>> would be better off with something that creates an alternating
>>> magnetic field.
>>
>>If the magnet was attached to a drill running at low speed then that would
>>cause an alternating magnetic field.
>
> Excellent point.
>
> Which brings up the question, what is the optimal frequency?
> With an electromagnet you get 50/60 Hz unless you go to a lot
> of effort to get another frequency - and it works well - but
> with a motor/magnet it's easy to pick a frequency.

The frequency is irrelevant. The point is to have a strong enough
magnetic field to line up all of the little magnetic thingies in
the media, and then turn them all around on the next half-cycle.

A permanent magnet will line up all the little thingies, but then
you've got a magnet bias that could introduce confounding factors
when re-using the media.

Anyway, with the AC field (hey, there's a usage of AC that we
didn't consider in the "Tastes Great-Less Filling" ACDC thing!),
just twirl the magnet fast enough that it can sweep the field
over the media once or twice.

Then, the secret is, slowly move the moving magnet ( or half
a transformer, or whatever) away from the media, and as the
alternating field gets weaker and weaker, reversing fewer
and fewer thingies, until on the average, there's no
residual magnetism in the media.

It's the same principle with CRT degaussers, but they use
a PTC thermistor in series with the coil. Press the degausser
button on your monitor - see the pretty patterns? And how
they decay? That's the principle that ends up with
negligible residual magnetization. I know there's a whole
nother jargon here, but, come on! :-)

Anyway, Hope This Helps!

Cheers!
Rich


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