[Beowulf] A Cluster of Motherboard.

Jim Lux James.P.Lux at jpl.nasa.gov
Thu Nov 10 22:52:28 EST 2005


At 04:19 PM 11/10/2005, Vincent Diepeveen wrote:


>At 07:10 AM 11/10/2005 -0500, Robert G. Brown wrote:
> >On Sat, 5 Nov 2005, oxylabtech at gmail.com wrote:
> >
> >> Hello
> >
> >could conceivably get some electrical oddities that destabilize things.
>
>Isn't shielding 50Hz fields pretty expensive, or do we speak of other type
>of shielding here, so not getting rid of the electro magnetic field?

Shielding for processor clock rate kinds of fields: tens or hundreds of MHz.

You can get problems with noise from one machine coupling into an adjacent 
one.  Very flaky, very hard to track down, very hard to predict.  Power 
supply isolation is also an issue.  You get clock rate transients on the 
power supply line, which couple into another board, where it moves the 
signals around a bit, just enough to cause problems, sometimes, when the 
phase of the moon is right, or the temperatures are just right and the 
board is running right at the ragged edge of the timing limits.


>I tend to remember mu-metal is one of the metals that gets used, as it
>completely eliminates 50Hz fields. One of problems is it that not much of
>it gets made, so a square meter thin mu-metal is already a couple of
>hundreds of euro.

Yep.. but hopefully, you're not shielding low frequency magnetic fields.

For what it's worth, steel works fairly well.  It just takes more steel 
than mu metal, so in a mass limited or space limited situation, mu metal is 
used (example.. shielding the CRT in an analog oscilloscope or shielding a 
photomultiplier tube where you are sensitive to stray fields).

As you noted, mu-metal is pricey.. you'd only use it if steel wouldn't fit.

>What other ways are there to get rid of the EMF?
>
>I mean *solutions where with a tesla meter i can measure there is not much
>of the radiation left*, i do not mean methods where one must believe on the
>blue eyes of the salesman that it shields;

Why Vincent, I have a bridge I'd like to sell you.... You seem such a 
trusting sort. The bridge is right near some prime land just east of Miami, 
Florida.



Jim Lux 

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