Hello All, In my opinion the length shall always be as the standard dictates and there are good justifications for the differing lengths in differing standards (even though the standard in question may not explain, but simply instruct).
For disturbance power, the length shall be around 6m. This is to pick up all standing waves from 30 MHz upwards. 30 MHz having a wavelength of 10m, so a length of >5m ensures that at least a half wave is present on the cable, meaning a peak (positive or negative) is measured. For CI, the test can be done up to 230 MHz and therefore the impedance of the cable between the CDN/clamp and the EUT must be limited to 0.3m max in order that the EUT receives the lion's share of the applied stress, rather than having a voltage drop across a relatively high cable impedance. For EFT, I would always cut the cable (to 0.5m or 1.0m, depending on which referenced basic standard is used, though the standard doesn't demand cutting the cable and states that bundling is fine). Again there are components in the EFT waveform that are in the many 100's of MHz. The attenuation of a 5.0m cable would severely round off the peak of the EFT waveform as seen at the EUT port. The surge waveform does not contain the high frequencies that EFT does and therefore lengths up to 2.0m are stated as acceptable. I don't think it's possible to standardise on a cable length for all EMC tests. It would cause huge disruption, and no single length fits all tests. Just to emphasise I have always cut down or made up lengths of cables to meet with the standard. It's a pain, but in my view it needs to be done, even when the standard permits bundling. If the customer doesn't want us to cut his cable, then it's a deviation from the standard and all deviations must be judged on an individual basis as to whether or not they are technically justifiable to demonstrate compliance with the standard. We may be able to test with long lengths but that doesn't mean we are testing to the standard. Best Regards, John -----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: 09 February 2011 07:20 To: [email protected] Subject: Re: [PSES] EUT power cord length In message <65d779430d6eb3468529ec67fa4a85510ce7fd4...@suspedu01001.us001.itgr.net>, dated Tue, 8 Feb 2011, "Schaefer, David" <[email protected]> writes: >If you think that is bad, try automotive standards for electronic >sub-assemblies. There are at least four different cable lengths you >need for a standard suite of tests. If it's not justified, we should campaign for change. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK Plural: data, criteria, phenomena. Singular: datum (different meaning: use 'data element' for a single item), criterion, phenomenon. 'Effect' is a noun, 'affect' is a verb (except in psychiatry). - ---------------------------------------------------------------- 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]> -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. - ---------------------------------------------------------------- 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]>
