[SI-LIST] Re: Chassis and Signal ground

What if the design has a serial port that could connect to a laptop or
PC that could have a much different chassis ground reference (difference
of several volts)?  Connecting chassis ground to signal ground could
crash the board, right?

-Chris


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=20
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir
> Sent: Wednesday, December 15, 2004 12:38 PM
> To: leeritchey@xxxxxxxxxxxxx; Peterson, James F (FL51);=20
> si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Chassis and Signal ground
>=20
>=20
> Lee, DC single pointing can work under the right conditions=20
> and may be=20
> required for safety in circumstances as I outlined to Jim.
>=20
> That said, DC single point connection does not eliminate AC=20
> paths, and can=20
> greatly reduce the SRF of the resulting structures.  For example, the=20
> proximity of a big signal ground plane near a chassis pan=20
> makes a nice big=20
> resonant cavity.  More often than not, a low cavity SRF is a=20
> bad thing that=20
> makes for efficient radiation / efficient reception across a=20
> broad range of=20
> frequencies.  This makes the folks who sell ferrite cable=20
> clamps happy, but=20
> not usually the poor compliance guy.
>=20
> Regards,
>=20
> Steve,
> At 08:46 AM 12/15/2004 -0800, Lee Ritchey wrote:
> >If I connected them at all, and I usually don't, it would be in only=20
> >one place, so that the opportunity for inceased EMI is held to a=20
> >minimum.
> >
> >Lee W. Ritchey
> >Speeding Edge
> >P. O. Box 2194
> >Glen Ellen, CA 95442
> >Phone- 707-568-3983
> >FAX-    707-568-3504
> >
> >I just used the energy it took to be angry to write some=20
> blues. Count=20
> >Basie
> >
> >
> > > [Original Message]
> > > From: Peterson, James F (FL51) <james.f.peterson@xxxxxxxxxxxxx>
> > > To: <si-list@xxxxxxxxxxxxx>
> > > Date: 12/15/2004 8:26:04 AM
> > > Subject: [SI-LIST] Chassis and Signal ground
> > >
> > > Chassis and Signal ground, what happens to our noise=20
> susceptibility=20
> > > if we connect them together on our cards (some of them are analog=20
> > > cards)?
> > >
> > > We've always kept chassis ground and signal ground=20
> separate on our=20
> > > cards
> >and
> > > connected them together on our backplanes. The reason we=20
> even have a
> >chassis
> > > ground on a board is because we use them as thermal=20
> layers that are=20
> > > used
> >to
> > > remove heat from boards (that need to operate in the vacuum of=20
> > > space).
> > >
> > > We are currently evaluating connecting our signal ground on the=20
> > > boards to the "card guides" of the chassis. The benefit=20
> is we don't=20
> > > need thermal layers anymore. The signal ground layers can now=20
> > > conduct the heat out through the guides and onto the=20
> chassis....but=20
> > > what have we done to our radiated noise levels and to our=20
> > > susceptibility to incoming noise?
> > >
> > > Regards,
> > > Jim
> > >
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