Hi Ian,
Hans makes some great points. I installed a grid system under my entire
building and all metal building structure is bonded to that around the
periphery. The shield room is bonded all four corners to this mesh. Power for
the chamber is supplied from a dedicated power supply, which itself is
Transformer isolated from grid power.
The goals were:
1) to make sure all metal stayed at the same potential in the event of a
lightning strike for safety.
2) to make all RF potentials on and near the shield room effectively zero. All
emissions instrument green wires use the room ground.
I have seen a number of cases where noise on the building structure ingresses
to the measurement through a ground connection. In thoese cases an inductor
has helped.
There are loads of compromises to be worked out. You may want to seek advice
>from a facilities guy, I suggest Wally Pilat of EMC Lab Services, but he's
located in the USA.
John Dearing of Teseq (UK) may know of someone local.
Cheers,
Derek Walton
L F Research
On 2/26/2010 12:44 PM, Hans Mellberg wrote:
It depends if you want a single point ground or a distributed ground.
For
some applications there is a recommendation to use a “ufer” grounding
scheme which is essentially a buried grounding grid.
At our building, we were able to drill through our concrete floor and
install
grounding rods about 8feet or about 2.5m deep into earth. No need to place the
shield room near the building’s side (unless you are above ground on a
multi-story building)
Our EMC semi-anechoic chambers were intentionally isolated from ground
and
only grounded at key locations per the manufacturer’s instructions. It would
seem that a multiple distributed grounding scheme might have been better.
Best Regards
Hans T Mellberg
Vice President of Engineering
Bay Area Compliance Laboratories
www.baclcorp.com
1274 Anvilwood Avenue
Sunnyvale, CA 94089, USA
(408)732 9162 x 3601
fax: (408) 732 9164
________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Ian
White (UK)
Sent: Friday, February 26, 2010 1:24 AM
To: IEEE Forum ([email protected])
Subject: Screened room move.
We are due to move our EMC screened room within the next year to a new
site.
It is planned to be placed in a much larger building of steel and
concrete
construction. We have planned it to be placed close to an outside wall so we
can pick up an outside earth which will be bonded in to the mass of the earth
for safety reasons
Could l hear your ideas on the best solution for earthing the screened
room
as l feel the present arrangement may be far from ideal. For example is it
better to use a number of rod earth electrodes or some sort of steel mesh
arrangement buried in the earth for a good RF performance.
Thanks for your help.
Regards
Ian White
(Project Engineer - Electronics)
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