Gents,
You might be happy to know, that according to the
USB 1.1 & 2.0 Specification standard,
http://www.usb.org/developers/docs/
the defined shield coverage for 1.1 & 2.0 USB cable is:
a minimum of a 65% tinned copper braided + aluminum
metalized polyester inner shield.
I can't help asking "what were the USB developers
thinking when they spec'ed such a thin cable shield
coverage?" Performing the 61000-4-6 test (on the
5M length USB cable) to an external box connected
to our product has certainly caused me gas! (New
product is tested to 60601-1-2 Rev 2.)
dave garnier
David Garnier
e GE Medical Systems
___________________________________________
David S. Garnier
Senior Technician
PET Engineering
3000 N. Grandview Ave - M/S W-1250
Waukesha, Wi. 53188
Tel: 262.312.7246
From: [email protected]
[mailto:[email protected]]On Behalf Of Ken Javor
Sent: Tuesday, November 18, 2003 9:32 PM
To: Ton Bouw; [email protected]
Subject: Re: Conducted immunity of a USB port
I can only answer parts of this question. You should test for the maximum
length the USB interface could attain, but since that length is 5 meters in
this case, the limit lower frequency should be tailored upwards to account for
that. There is no use testing at 150 kHz on such a short cable. This is
right out of IEC 61000-4-6.
If CDN design presents obstacles to testing high speed USB, I think an EM
clamp is a better approach. In fact, I believe an EM clamp is a better
approach for any shielded cable. The point of a CDN is to inject a signal
into an equipment connector pin. When a cable is shielded, the mechanism for
getting the rf signal on a pin is the transfer impedance of the shield. In
order to test that, you need to get current flowing down the length of the
shield. I think an EM clamp is a better mechanism for achieving that.
From: Ton Bouw <[email protected]>
Reply-To: Ton Bouw <[email protected]>
List-Post: [email protected]
List-Post: [email protected]
List-Post: [email protected]
List-Post: [email protected]
Date: Tue, 18 Nov 2003 23:51:07 +0100
To: [email protected]
Subject: Conducted immunity of a USB port
Dear group,
I have the following questions on testing a USB port for conducted immunity
1) USB extension cables are available in the consumer market. The USB 1.0 spec
limits the cable length to 5.0m. Therefor I believe that the conducted
immunity test is required even if the cable length of the DUT is less than 3m,
unles a restriction is made in the user manual.. Is that correct?
2) I tested conducted immunity using a CDN-S9 with home-made adaptors from DB9
to USB using 4 pins of the DB-9 and the screen connection. I assume that this
should give a representative result?
For information: this does not work for hi-speed USB because of the LPF in the
CDN.
3) Are CDN's for USB available? Or is it better to use an EM clamp?
kind regards,
Ton Bouw
