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Dave, I agree the USB spec didn't take into account the more strict industrial applications and immunity tests. We use the USB interface to communicate with an instrument that can be used in a light industrial environment. The interface will not function during a Level 3 Fast Transient Burst test (2KV) with an off the shelf cable. So we have to make what we call a "Super USB Cable" by cutting off the jacket of a standard cable, running the cable through a heavy braid, then soldering the braid to the metal shell at each end. With this modified cable, we get good results for all immunity tests.
Making this cable is a pain so if anyone knows of a manufacturer of a better quality USB cable please let us know. Best regards, Brian Kunde LECO Compliance Testing Center "I'm pull for ya, we're all in this together" (Red Green) ____________________Reply Separator____________________ Subject: RE: Conducted immunity of a USB port Author: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: 11/19/03 12:30 PM Gents, You might be happy to know, that according to the USB 1.1 & 2.0 Specification standard, http://www.usb.org/developers/docs/ <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 This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: with the single line:Title: Re:RE: Conducted immunity of a USB port
Dave,
I agree the USB spec didn't take into account the more strict industrial
applications and immunity tests. We use the USB interface to communicate with an
instrument that can be used in a light industrial environment. The interface
will not function during a Level 3 Fast Transient Burst test (2KV) with an off
the shelf cable. So we have to make what we call a "Super USB Cable" by cutting
off the jacket of a standard cable, running the cable through a heavy braid,
then soldering the braid to the metal shell at each end. With this modified
cable, we get good results for all immunity tests.
Making this cable is a pain so if anyone knows of a manufacturer of a better
quality USB cable please let us know.
Best regards,
Brian Kunde
LECO
Compliance Testing Center
"I'm pull for ya, we're all in this together" (Red Green)
____________________Reply Separator____________________
Subject: RE: Conducted immunity of a USB port
Author: [email protected]
Date: 11/19/03 12:30 PM
Gents,
You might be happy to know, that according to the
USB 1.1 & 2.0 Specification standard, http://www.usb.org/developers/docs/
<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
-----Original Message-----
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]>
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
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