"rafts of disagreement" ?? Not here, almost never, on occasion. Most equipment with a USB interface will require the EMC tester to rely on external equipment. For a USB port, the EMC standard would have to define both the hardware layer and the data layer, or the report must define these test conditions. The only thing that comes to mind is to connect the host port to a defined 'data LISN' that would support max data rate, and then put the external equipment in a steel box so that the only think 'exposed' is the UUT.
There are problems with defining USB test conditions at both the hardware and data layers (as with some other data ports). There is no single standard data rate, no standard frame rate, hosts are both differential and single ended, variable sync word length, variable data packet size, a hub or other connected device may or not be isochronous to the host channel, and there are at least four different data transfer types - some are bursty and some are periodic. Etc, etc. And there are multiple configs at the hardware layer. The attach detection protocol will only work if the host sees at least 1uF on the power line at a physical port, but does not define the host port output Z; anything on a USB host channel can be either powered thru the bus or self-powered; a hub may or may not be self-powered; etc, etc. But, when I wear my code-monkey hat, I luv that damn USB port. Brian -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: Monday, May 09, 2011 1:19 AM To: [email protected] Subject: Re: [PSES] Opinion regarding USB and EMC testing In my opinion, it seems inappropriate to rely on equipment, external to the test subject, to determine emissions performance. i.e. the attenuating effect of whatever your USB device is connected to, which will be highly variable between various hosts. The test subject should be assessed in its own right. In the absence of a conducted emissions test in the directly applicable standards, I would be tempted to ‘borrow’ or apply an appropriate test from another EMC standard. e.g. Conducted Emissions DC Emissions from, say, EN 301 489-1. This uses the method and limits from EN 55022 but using a DC power source. I would feel I’ve done all I should to determine the USB device’s emissions. Awaiting rafts of disagreement…… Tony - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
