Hello Muriel, If you add a reactive filter in a line what you conceptualy do is a short circuit (if paralel capacitor) or an open circuit (if serial inductor) at certain frequencys (the frequencys you want to regect). This transforms the line in a sort of dipole (if open) or loop (if short) that can radiate the energy of the interference. That sort of antenna will be far in general from being adapted to the interference generator so you will have reflections as well.
So I thing you are right, a filter can increase radiation and can increase internal noise. Solutions: 1_ Disipative filters (with ferrites) are not reactive but resistive at the frequency of the interference so you can minimize reflections and antena behave. 2_ Mounting the filter in a way that minimizes the lengh of cables carrying interference. But, ... The filters regect between 100kHz to 30MHz and no more (the ones I've seen) and the radiations are measured between 30MHz and 1GHz. So whith filter or without the radiations of interest (the ones that can make you fail the test) are the same. I'm talking theory and I know real live have surprises. If someone out there have had an experience of increasing radiation when adding a filter I'm sure will say something. And a little reflexion to think over: You can have a 10.000 V generator. No energy will flow out if you let it open circuit. Can't you apply the same concept to the energy of the interference? Regards, Joan Castell UPC University Catalunya. En/Na Muriel Bittencourt de Liz ha escrit: > 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? > > - 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?? > > Thanks in advance for your attention. > > Regards, > > Muriel Bittencourt de Liz > Ph.D. Student > Interest Areas: EMC for power electronics, RF measures, EM interference > Federal University at Santa Catarina State > Florianópolis, Santa Catarina, Brazil > > ------------------------------------------- > 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: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: pstc_ad...@garretson.org > Dave Heald davehe...@mediaone.net > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > 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. ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
