The severity of the test using a CDN is much more repeatable compared to the
EM-clamp. With a clamp test, how the auxillary end of the cable is terminated
has a profound affect on the test since it affects the total circuit
impedance. It could make the test either less or more severe. This is where
subclauses 7.3 and 7.4 of 61000-4-6 come into play.
If I were to test a shielded cable using an EM-clamp, I would short the cable
shield to the ground plane on the AE side. This would lower the overall
circuit impedance, making it a more severe test in most cases. Then I would
use a feedback probe on the EUT side to measure the induced current and limit
the induced level based on that measurement, according to subclause 7.4 of the
standard.
Obviously, when allowed, the preferred method is to use a CDN for shielded
cables.
Bob Richards, NCT
--- On Wed, 1/7/09, Sterner, David (NY80) <david.ster...@honeywell.com> wrote:
From: Sterner, David (NY80) <david.ster...@honeywell.com>
Subject: RE: EN61000-4-6: coupling to shielded cable
To: "Charles Blackham" <charles.black...@sulisconsultants.com>,
emc-p...@ieee.org
Date: Wednesday, January 7, 2009, 11:10 AM
Charlie -
The immunity document for security systems, EN 50130-4, specifies a CDN
for screened cable; we use the Fischer CDN on video cable. EN 55024
(ITE) does not specify a test procedure for screened cable. Our
comparative results on the same 75-ohm cable link indicate that the
CDN-75 provides a much more severe stress than the (Fischer) E-M clamp.
Outlook:
Products that 'pass' using the E-M clamp on sccreened cables are very
likely to fail if retested, i.e. by an agency or an OEM customer.
E-M results on video products are likely to give one a false sense of
security; image degradation will be more severe with the CDN.
_ Honeywell
David W. Sterner
Quality Assurance Engineering
2 Corporate Center Drive Suite 100
P.O. Box 9040
Melville, NY 11747
Phone: (516) 577-2321
Fax: (516) 577-3540
david.ster...@honeywell.com
<http://www.honeywell.com>
-----Original Message-----
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Charles
Blackham
Sent: Wednesday, January 07, 2009 1:49 AM
To: emc-p...@ieee.org
Subject: EN61000-4-6: coupling to shielded cable
Group
We have a unit with a 2-wire shielded signal cable that falls under
EN61326-2-3 and also requirements of NAMUR (automation technology in
process industries).
We have been performing EN61000-4-6 Conducted Immunity tests on the
shielded cable using a coupling clamp as the injection method, however
client is requesting we use a CDN
Does anyone perform such testing using a CDN?
regards
Charlie
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