[SI-LIST] Re: Chassis and Signal ground
- From: "Derek Walton" <lfresearch@xxxxxxx>
- To: Charles.Grasso@xxxxxxxxxxxx
- Date: Wed, 15 Dec 2004 19:01:51 -0600
HI Jim,
I guess the answer is, it depends...
In a nutshell, if you have a typical aerospace metal enclosure, and your
interfaces are protected against Single and Multi Stroke lightning, then
this can work.
In my courses I try to convince folks to treat the chassis as the
"drain", the location to where undesireable signals are sent. Since most
aerospace boxes are designed with filters ( this means transient filters
too ) at the point signals enter the enclosure, the noise current on
the chassis is relatively well defined. It's a reasonably simple matter
to keep that away from sensitive areas of the circuits. There are pro's
and con's
On the pro side, the current on the inside of the enclosure as a direct
result of capacitive coupling from any point in the internal circuits
where dv/dt is occuring, has a very low Z return path. By being low Z
and internal to the enclosure, the emissions can be lower.
On the con side, if noise is allowed out on interconnect wiring, then
the loop formed between the wiring and the ground plane is huge, and
even though current may be small, the radiating effiency is high.
As Chas said, the overall design philosophy is critical. When well
thought out, there are many effective ways to skin a cat.
Good job they have 9 lives!
Cheers,
Derek.
Grasso, Charles wrote on 12/15/2004, 4:45 PM:
> Be very careful here. I suggest you contact a EMC consultant
> to review the overall design.
>
> Best Regards
> Charles Grasso
> Senior Compliance Engineer
> Echostar Communications Corp.
> Tel: 303-706-5467
> Fax: 303-799-6222
> Cell: 303-204-2974
> Email: charles.grasso@xxxxxxxxxxxx;
> Email Alternate: chasgrasso@xxxxxxxx
>
>
>
> -----Original Message-----
> From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx]
> Sent: Wednesday, December 15, 2004 9:16 AM
> To: si-list@xxxxxxxxxxxxx
> 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
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
