Re: Electronic Box Shielding ?

On 27 Nov, CAD_CAM_EDM_DRO@egroups.com wrote:

> SO, if I build a box for my electronics and ground this
> box will it supress electromagnetic energy escaping the box?
> I'm sure it can so now for the real questions, does the box
> need to be steel, i.e. magnetic, or will aluminum work as
> well??

The single biggest source of RADIATED EMF, by far, is all the
transmitting antennas you have coming out of the box.

Antennas ?

Yes, the wires running from the box to the steppers are a form of
longwire antennas, and longwires are most efficient. If you are in
fact concerned about radiation, you certainly want to shield those
connections inside some conduit.

Now, I have my doubts about how much noise will actually be radiated
by your stepper system, but as these leads need some protection anyway
against hot chips and whatnot, encasing them in flexible conduit is
just good common sense.

A much more troublesome area is noise travelling along the power line.
This is best handled by a GOOD quality line filter .. may be two of
them .. and proper grounding techniques inside the box.

Again, a stepper based system is unlikely to create enough energy to
cause some other device problem, but put one in anyway.

The reverse is not true. Other devices putting energy on the line CAN
cause problems for the stepper electronics and/or the CPU. One such
source that I'm intimately familiar with is VFD controllers. There,
the energy IS large, both radiated and induced.

As far as materials go, any metal box will trap a lot of the RF energy.
Trapping it all is impossible and even trapping most sends strong men to
tears. Just ask anyone who's had to deal with FCC Certification issues.

> Then if I connect the ground from this box to a step up
> transformer and plug it into the wall, can I make my electric
> meter go backwards? Only kidding in this paragraph. :-)

Don't laugh - capacitive flourescent ballasts are illegal because
they'll do exactly that. Some phase relationship thing with the
inductance of the meters.

Alan

--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta