In message <9d04b979323dcd428297dda95108893e03557...@bb-corp-ex2.corp.cubic.cub>, dated Fri, 6 Nov 2009, "Price, Edward" <ed.pr...@cubic.com> writes:
> >When "millions of products that operate without any problem" suddenly >become non-compliant with a standard, doesn't that mean that the >adjustment should be made to the standard and not the products? It isn't as simple as that. However, the 'grandfather' clause in IEC/EN 61000-4-7:2002 does just that, which is why throwing doubt on its validity is reprehensible. The trouble with low-frequency conducted EMC is that when an EMC problem crops up, it can be extremely difficult and costly to fix it. And the *potential* to cause a problem has to be considered, as well as the current position. For example, there seems to be no product in use at present that produces a significant interharmonic emission current within a certain band between 200 Hz and 250 Hz. But if such a product appears, it could disrupt automatic electricity meter tariff switching in a European country, affecting millions of people as well as the electricity suppliers. Many of these EMC problems that do occur are very localized, so wide-area surveys report that 'all is well', but smoke is coming out of the system in just a few places. The situation worsens at higher frequencies, because of the high voltages that can be developed across inductors, in the supply system and in load equipment, and the high currents that can flow in capacitors in load equipment. The emission spectrum of large variable-speed drives can extend well beyond 9 kHz, and for smaller 'switching' products, 10 MHz is not the limit. In summary, we DO need interharmonic emission control, it's getting there that is so 'fascinating'. -- 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 Help stamp out intolerance! - 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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 <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
