Chassis Ground layout for better ESD and EMI compliance

Why isolate the PCB ground from the chassis? The best thing to do is bolt the (single!) PCB ground plane to the chassis as many places as possible, and ground the connector shells to the chassis, too.

John

Thanks John. Isolated the chassis and signal grounds for better ESD immunity.

-M

But you're making it worse!

The pattern is familiar: isolate grounds for some reason, then get cold feet and add networks between the isolated ground and the chassis ground to try to make them the same potential.

I have a customer who is doing that to me now: insisting on isolation, and insisting on a network to bypass the isolated ground to chassis ground. The details are even worse. Makes no sense.

This same customer insists on shielding all cables, but grounding the shields at one end only! Nominally the source end; but the cables have signals going in both directions!

I tried to give them an analogy they could understand:

Imagine the end of a garden hose. Imagine a bunch of twigs sticking out the end. Grab the end of the hose and shake it. What happens to the twigs?

John

try using a small choke, it provices DC path, but limits AC noise.

Best place is near PS, and one only if you can to prevent ground loops

The 1 meg are more for static bleed.

The areas where the screws are should be compliantly plated. Nickel, gold, whatever reduces dissimilar metal effects and thus corrosion. And _no_ solder, a very common mistake. Solder tends to creep under pressure and the mechanical force gradually sags. Worst case the screw works itself out during a lengthy and rough transport.

Another common mistake is to have the clearance too small. Then a washer may partially ride on the soldermask, not a good thing.

They grow roots into the hose?

Recognize this?

ftp://jjlarkin.lmi.net/Zeit.jpg

John

Ground early and often! ...except where you can't. :-(

BTW, John, what's your take on this (I have the problem, in spades):

Can't read the upper word but this is funny. They had to cancel one day of the Amgen tour. This Sunday we had snow here in the foothills, at elevation 1400ft. In the middle of May!

Oh, yeah, how could I forget. Hot is global warming and cold is always just weather. Right?

Of course not! Hot is "global warming" and cold is "global climate change".

If you must use these for safety reasons: Capacitive stitching has about the same effect at the test lab as a super-loud muffler has on the sheriff who just stopped a kid for speeding ;-)

Then one also has to worry about the reverse path. What if some large EM spike gets in?

No way to use optocouplers instead? It'll be cheaper, too.

The sticker says Zeitgeist Racing Team. Or maybe Zeitgeist Drinking Team. It was kinda hard to photograph.

"Warm Beer * Cold Women"

They had to cancel one day

Lots of snow, and some rain, in Truckee last few days.

ftp://jjlarkin.lmi.net/CABIN.JPG

I just got an email from Alpine Meadows. They are re-opening for skiing for the 4th of July weekend. They got 72 feet of snow this year.

All the reservoirs are full, and the melt has just begun. Long, hot showers. So much for the idiot climate predictions.

John

Some day we'll have to meet there for a burger and Chimay Triple.

A few years ago that was different but today I couldn't name one person in this whole neighborhood who still believes AGW is true. Bill Sloman could go door to door and stomp his feet on the ground, it won't change their minds. Ok, this ain't San Francisco but it's still California.

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Aren't we near the bottom of the 11 year solar cycle? In five or six years there will be a different tune again.

We're having record rains, here in Western NY. So muddy, that driving the tractor means leaving 6" (15cm) tracks in the yard.

George H.

Maybe next time you should try actually reading the post.

Apparently huge places, like lots of India and China, are feeding their people from agriculture based on over-pumping aquifers. And they are running out. If anything ever revives our balance-of-trade fiasco, it will be food.

John

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Hmmm, Isn't there some aquifer in the mid-west that our farmers are pumping dry?

Too much water in the Mississippi and not enough in Texas.

George H.

No, it increases noise.

Ground loops are good. It means you're keeping everything grounded.

John