RE: [SI-LIST] : Single versus multiple point grounding ...

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From: Grasso, Charles (Chaz) (GrassC@LOUISVILLE.STORTEK.COM)
Date: Wed Oct 27 1999 - 19:25:19 PDT


Excellent response
Thank you
Charles Grasso
StorageTek
2270 Sth 88th Street
Louisville CO 80027
Tel: (303)673-2908
Fax(303)661-7115

> ----------
> From: D. C. Sessions[SMTP:dc.sessions@vlsi.com]
> Sent: Wednesday, October 27, 1999 5:15 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Single versus multiple point grounding ...
>
> Douglas McKean wrote:
> >
> > From: Denomme, Paul S. [mailto:Paul.Denomme@viasystems.com]
> > >
> > > Regarding comment 2, he was stating that grounding in
> > > multiple locations is a bad idea. This can create some
> > > ground loops within the chassis. There will be some type
> > > of potential difference from one chassis connection
> > > point to another and this will create some current
> > > in the chassis. This is very bad from an EMI perspective.
> > > He believes one Solid connection to the ground plane is sufficient.
> > >
> > > I would like to hear a take from an EMI person.
> >
> > Well, personally I'd like to see some measured
> > results from testing that prove this opinion.
> > I've used multiple point grounding in real system
> > design with great success for not only EMI but
> > for ESD robustness. The fact that I instituted
> > multiple point grounding from a former design
> > single point grounding that had sufficient problems
> > to warrant a redesign and that such redesign worked
> > was proof enough for me.
>
> In many ESD situations multipoint grounding is a Good Thing
> because it minimizes the net local change in potential for
> strikes far from the groundpoint. OTOH it can cause problems
> in extreme cases if the chassis is relatively high impedance.
>
> For EMI the same tradeoff applies. A multipoint connection
> to the chassis will be good if the chassis itself is low
> impedance and the contacts are relatively high impedance.
> A single-point ground *can* be a problem if the enclosure
> impedance is high enough that internal fields can induce
> potential differences across it; in that case shunting the
> induced currents through internal conductors may be better
> than leaving the skin to flap around.
>
> --
> D. C. Sessions
> dc.sessions@vlsi.com
>
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