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From: "Tom Faloon"
Subject: Re: Bypass RS-485 shield--ESD problem??
Date: Tue, 1 Oct 2002 21:17:51 +0100
NNTP-Posting-Date: Tue, 1 Oct 2002 20:12:48 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Are you certain that the problem is due to RF getting in via the shield?
It may well be, but are you sure?
What have you used for common between devices.
A separate 'third wire'?
Is it grounded anywhere?
I don't like the shield connected to 'common' via 100 Ohms.
I know that's what the data sheet says, but I'm not impressed.
Tell us a bit more.
Jim H wrote in message
> I am getting RF leakage into my controller (Maxim 1480B based) from
> the shield of the signal cable on my 8 node 1200 Meter Rs 485 network.
> Shield is grounded thru 100 Ohms per datasheet. I will add a ferrite
> bead at the control end to try to keep the unwanted RF (80-130
> Mhz)energy out. If that doesn't work - I would like to bypass the
> shield at the other nodes with a 100 nf cap - but won't this become a
> part of the ESD picture? I need to preserve my 15 KV ESD rating for
> CE compliance.
> BTW I have read the datasheet, App Notes and especially the relevant
> posts in this forum. Thanks in advance for your help.
> Jim Harris
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