-----Oorspronkelijk bericht-----
Van: Cefalo, Lisa <[email protected]>
Aan: [email protected] <[email protected]>
Datum: donderdag 26 maart 1998 3:25
Onderwerp: any insight appreciated
Hello all,
I was wondering if any of you may have some insight or experience
or recommendations about the following dilemma: We use a rather
complex keypad/front panel on one of our pieces of equipment. This
panel, in it's manufacture, consists of several different layers,
polycarbonate, adhesive. etc.. One of these layers is a shielding
material spec'd at 10ohms per square.
This is very high compared to a metal enclosure: you can expect that it does
not contribute
very much to total screening fo EMI. From EMI point of view this is almost an
opening.
We would like to go to a 20
ohms per square material but are cautious about the potential effects
on the EMC characteristics (emissions, esd, etc.).
For ESD this is not bad too. Goal in ESD is to get rid of fieldstrength
esp. for LCD displays, and to reduce discharge current. Both are met for 10 and
20 ohms
per square, the latter even better. Immunity is always better when no direct
discharge
can take place on the conductive part of the foil.
The window itself
is grounded by contact with a silver mesh which in turn is grounded
via conductive cement to studs that attach to the metal bezel. I
expect in comparison with the actual resistance of the ground path
the change from 10 to 20 ohms is small.
In the interest of time and money, the debate is to re-test or not,
and which tests... Any comments or help would be appreciated.
Thank you,
Lisa
If you EMI performance is close to the limit (say within 6 dB), you better
re-test. Consider ESD retesting too if direct discharge on the conductive part
can take place.
If you want to be safe, or follow the EMC-directive: RE-TEST everything.
Hope i've been of any service to you.
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