[SI-LIST] Re: Chassis ground
- From: "Rich Peyton" <p2rich@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 21 Jun 2001 14:56:17 -0400
I was ordering McGraw -Hill "Handbook of Essential engineering information &
Data"- By Ganic & Hicks (Anyone have it?) and stumbled across this which may
have info your looking for:
"Electrical Grounding: Bringing Grounding Back to Earth"
by Ron O'Riley, Ronald P. O'Riley
Rich
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of S. Weir
Sent: Thursday, June 21, 2001 1:25 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Chassis ground
Alex,
There is a good explanation of the effects in Mark Montrose's book "EMC and
the Printed Circuit Board", as well as some others. If you consider that
the return path(s) from digital ground to chassis is an antenna, then the
more connections, and more closely spaced you have, the poorer the antenna
gain, and the better the EMI performance.
As to the DC currents, this is a safety issue. You do not want to
electrify the frame. Make sure that your power system is such that if any
of the external power leads are cut, the frame does not complete the path.
Regards,
Steve.
At 09:28 AM 6/21/01 -0700, you wrote:
>I know most SI engineers work at the board level but I am often asked if
>digital signal ground should be connected to the chassis ground at the
board
>(normally through standoffs). It seems to me that the chassis would be a
>very high impedance signal path so in effect only DC currents would flow
>thus becoming part of the power supply return. Is there any advantage to
>keeping the chassis ground isolated from digital ground and connecting them
>at a single point with the green AC wire? I'm asking from the point of view
>of reducing EMI.
>
>I'm talking about your typical high speed digital systems with multiple
>boards in a large chassis. Also, assume no conductive connections to the
>outside world (optical only, or unshielded Ethernet).
>
>
>
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