[SI-LIST] Re: Chassis Ground connected to Signal Ground

Alan,

It depends on how your system is powered.  If you have a low voltage system 
that powers through cables, and logic ground ties to battery return, then 
you need to be aware of regulatory requirements on 
electrification.  However, if the external power return is isolated from 
the logic ground, then this is not an issue and the quietest and most 
robust EMC results from frequent bonding between chassis and logic 
ground.  The smaller the loops, the less efficient the antennae that form.

 From an SI standpoint, if you have multiple boxes tied together, and you 
bond the grounds then you can get circulating currents that affect 
low-level analog, like audio.  One way around that is a saturable reactor 
in series with the green wire.

Regards,


Steve.
At 09:22 AM 6/17/2004 -0600, Pfeifer, Alan wrote:
>Hi Experts,
>I am using a metal cage that protrudes through the bulk head of a product.
>In the past, we connected the pins of that cage to ground through 1000 pF
>caps.  While monitoring this list a few months ago, there was a long
>discussion on the connection of logic and chassis grounds.
>
>My question is this:  Is it better to use the 1000 pF caps to tie the
>chassis ground to the logic (signal) ground or better to tie the two grounds
>directly together?  I am interested in both SI issues and EMI issues.
>
>Thanks,
>Alan
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