From: firstname.lastname@example.org (carltons)
Subject: Re: Grounding advice
References: <3D9DFA4D.email@example.com> <3DA726DB.firstname.lastname@example.org> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sun, 13 Oct 2002 02:26:30 GMT
Date: Sun, 13 Oct 2002 02:26:30 GMT
In article , John Larkin
> On Fri, 11 Oct 2002 23:19:50 -0400, Keith R. Williams
> >In article <firstname.lastname@example.org>,
> >jjlarkin@highSNIPlandTHIStechPLEASEnology.com says...
> >> On Fri, 11 Oct 2002 19:30:47 GMT, Ryan Gammon
> >> wrote:
> >> >I happened to come across the following in AoE (pp853):
> >> >
> >> >"... we suggest as many redundant ground connections as possible...
> >> >... Don't worry about about "ground loops" in a digital or RF circuit;
> >> >that's a microvolt audio circuit issue"
> >> >
> >> >
> >> Now *that* is one of the few sensible statements ever made on the
> >> subject.
> >I took a course (professional, rather than academic) in EMI
> >abatement, measurement, and standards a couple of years ago (I'm
> >now an official EMI Guru (tm) ;-). One of the points was that
> >ground loops are meaningless above audio frequencies. At RF
> >frequencies the induced currents will cause loops even if
> >connections don't. The theory then was to maximize ground
> >connections, even in metal parts (unconnected gaps in metal,
> >a.k.a. slots are antennas as much as wires are).
> > Keith
> I may have to hire you to say that in front of one of my customers.
> They're building a pulsed-power widget, and I'm doing the timing box,
> and their Pointy-Haired-Boss (tm) insists that we ground nothing
> because 'it would create ground loops'. He thinks cable shields should
> be grounded at the source end only! By deftly (mis)managing a couple
> of design reviews, I managed to ground *everything* to my metal case
> and present a fait accompli (French for 'fooled you, Jack!')
> prototype, which we don't have time to change.
> Vision: a couple of dozen metal boxes, all isolated from the nice
> solid-metal baseplate, connected by a spider's nest of crisscross
> cables carrying power, logic, and low-level analog signals, all
> ringing like the Bells of Saint Mary's every laser shot... nightmare!
I've been doing rf design for 25 years now and I'm still no guru on
grounding. One thing is true, however, the only thing better than lots of
ground is more ground! Also, depending on freq, ground is not always
ground. This fact drives the new engineers crazy. I even worked on the
APCOR medical radio where one of the board schematics had a capacitor
showing it going from ground to ground. Explain that one to one of your