This can be a little confusing. In a previous post: < < Magnetic fields tend to build up low value EMF sources in series with loops and have extremely low impedances. When any electronic circuit contains loops, at a low impedance level, this circuit will almost certainly be affected by the test's field. You may think of low impedance wheathstone bridges,< < If we are talking about the susceptibility of a given (VICTIM) circuit to external magnetic fields, then circuits with HIGH impedance loads are most susceptible. See Ott 's "Noise Reduction Techniques...." page 40, Paul's "Intro. to EMC", page 522. If the focus is on the SOURCE (or aggressor) circuit, then it is reasonable to say that low impedance circuits with their associated, (and assumed) large di/dt create crosstalk problems dominated by inductive coupling. But from the discussion I assumed that the focus was on the VICTIM circuit during immunity testing, where an Mdi/dt voltage is induced into a victim circuit. In this case circuits with LARGE load impedances are most susceptible. For circuits that are large compared to the noise wavelength, it may be better to talk about far end and near end coupling, rather than simply "low impedance" or "high impedance" loops. All of these discussions presume that the victim circuit uses voltage signaling to convey information. If the discussion is about circuits that use current signaling (a 4-20 mA loop,or a transimpedance amplifier), then it may be better to talk about the effect of source or load impedance of the victim circuit on the induced noise current level in the victim circuit.
Regards Lee Hill Silent Solutions LLC EMC & RF Consulting and Training lh...@silent-solutions.com www.silent-solutions.com -----Original Message----- From: Gert Gremmen : ce-test, qualified testing [mailto:g.grem...@cetest.nl] Sent: Wednesday, March 27, 2002 2:32 AM To: Jim Ericson; emcpost Subject: RE: Scope of EN 61000-4-8 (Power Frequency Magnetic Testing) Hi Chet, There are many other standard electronic equipment that qualify them for these tests; possibly not in the phase of compliance seeking, but at least when looking for simple quality. Magnetic fields tend to build up low value EMF sources in series with loops and have extremely low impedances. When any electronic circuit contains loops, at a low impedance level, this circuit will almost certainly be affected by the test's field. You may think of low impedance wheathstone bridges, audio output amplifiers; virtual ground sink input in opamps and many other applications. Also, in high end, low level or high dynamic range equipment , the EMF value induced by the field may directly cause performance issues . For this to happen one does not need a low impedanc e path. Finally any equipment containing air coils, or any other non closed magnetic field loop coil may pick up EMF voltages from this test. If these EMF source that buil up in the coil cause a performance problem is entirely dependent of the design, of course. It's for this reason that for professional audio systems EN 55103 the application of a magnetic field source test is prescribed for the full audio frequency range. Looking just at VDU and Hall sensors is a bit restricted, although i definitely agree that for power frequency issues they are the vast majority. Regards, Gert Gremmen Ing. ce-test, qualified testing ce-marking & more http://www.cetest.nl ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com 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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
