I read in !emc-pstc that Muriel Bittencourt de Liz <[email protected]> wrote (in <[email protected]>) about 'physics behind EMI powerline filter', on Mon, 3 Dec 2001: > > >Hello Group, > >I have a "long-time" question, concerning the energy issues in a EMI powerline >filter. > >I'll put a case, and ask the question after. > >This is the case: > >- When trying to minimize the conducted emissions from a electrical equipment >/ >circuit, one of the things to do is to put a EMI filter at the power entrance. >This filter can be from a manufacturer (ready filter) or you can make one >(with >common mode inductors, capacitors, inductors). > >This are the questions (they arearelated, i.e., complete each other): > >- What, physically speaking, happens to the EMI energy that leaves the >equipment >when I add a filter??? When there is no filter, I understand that the energy >goes to the mains?? Does the filter reflect the EMI energy, keeping it >"arrested" inside the equipment?
Some is dissipated in resistive losses in the filter, some is indeed reflected back into the equipment, where it is also eventually dissipated in resistive losses. > >- Thinking under the light of the principle of energy conservation, what >happens >to the EMI energy when I add a filter?? It cannot be lost... > >- ... And, supposing that the energy keeps arrested inside the equipment, >isn't >it worse for radiated emissions?? i.e., it can increase the level of radiated >emissions?? That might occur, but generally conducted emissions are stronger at low radio frequencies, which are not radiated efficiently because the equipment is physically smaller than a half-wavelength. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
