[SI-LIST] Re: Chassis and Signal ground
- From: steve weir <weirsp@xxxxxxxxxx>
- To: Ron Matthews <rmatthews@xxxxxxxxxx>, leeritchey@xxxxxxxxxxxxx, "Peterson, James F (FL51)" <james.f.peterson@xxxxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Fri, 17 Dec 2004 08:11:16 -0800
Ron, thanks for the kind thoughts. I always enjoy Dr. Archambeault's
presentations on the telegraphy origins of the term ground, and the
frequent fallacies held with regard to returns.
Regards,
Steve.
At 08:20 AM 12/17/2004 -0500, Ron Matthews wrote:
>That's an excellent point, Steve. So many times engineers think that their
>single-point "ground" is applies from DC-to-daylight.
>The coupling paths that we can't see will often negate the notion of
>single-point-"ground" at higher frequencies.
>
>In addition to Henry Ott's book, Bruce Archambeault of IBM also gives an
>excellent treatment of this topic in his book "PCB Design for Real World
>EMI Control".
>
>Regards,
>
>Ron
>
>
>Ron Matthews, NCE
>Principal MTS
>Signal Integrity/EMI
>Charles Stark Draper Laboratory
>555 Technology Square, MS 62
>Cambridge, MA 02139
>Voice: 617-258-2519
>Fax: 617-258-1998
>Email: rmatthews@xxxxxxxxxx
>
>
>
>At 09:37 AM 12/15/2004 -0800, steve weir wrote:
>>Lee, DC single pointing can work under the right conditions and may be
>>required for safety in circumstances as I outlined to Jim.
>>
>>That said, DC single point connection does not eliminate AC paths, and can
>>greatly reduce the SRF of the resulting structures. For example, the
>>proximity of a big signal ground plane near a chassis pan makes a nice big
>>resonant cavity. More often than not, a low cavity SRF is a bad thing that
>>makes for efficient radiation / efficient reception across a broad range of
>>frequencies. This makes the folks who sell ferrite cable clamps happy, but
>>not usually the poor compliance guy.
>>
>>Regards,
>>
>>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 one
>> >place, so that the opportunity for inceased EMI is held to a 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 blues.
>> >Count 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 susceptibility
>> if we
>> > > connect them together on our cards (some of them are analog cards)?
>> > >
>> > > We've always kept chassis ground and signal ground separate on our cards
>> >and
>> > > connected them together on our backplanes. The reason we even have a
>> >chassis
>> > > ground on a board is because we use them as thermal layers that are used
>> >to
>> > > remove heat from boards (that need to operate in the vacuum of space).
>> > >
>> > > We are currently evaluating connecting our signal ground on the
>> boards to
>> > > the "card guides" of the chassis. The benefit is we don't need thermal
>> > > layers anymore. The signal ground layers can now conduct the heat out
>> > > through the guides and onto the chassis....but what have we done to our
>> > > radiated noise levels and to our susceptibility to incoming noise?
>> > >
>> > > Regards,
>> > > Jim
>> > >
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