Did adding phase requirements: - Narrow the LISN performance characteristics, taking into account component parasitics & component tolerances? - Address the possibility of interaction between LISNs & system EMI filters? - Justify publication of a new edition of the standard that we have to buy?
Pat Lawler EMC Engineer SL Power Electronics Corp. [email protected] wrote on 04/20/2011 10:56:42 AM: > Don, I still can't see what additional characterisation phase > response check would provide for a simple passive network (like a LISN). > For example, if the LISN amplitude response rolls at constant > 20dB/decade, doesn't that imply a constant phase shift? > And, doesn't the rate of change of phase-shift predict a unique > amplitude response? I thought it must. > > I can't shake the feeling that an amplitude-response and phase- > response go hand-in-hand. I didn't think it mathematically possible to > have anything else. > _____________________________________ _______________________________________________ > > Ralph McDiarmid | Schneider Electric | Renewable Energies Business | > CANADA | Regulatory Engineer > > > From: [email protected] > > To: [email protected] > > Date: 04/20/2011 07:09 AM > > Subject: Re: [PSES] LISN Phase angle, why? > > Ralph- > > The answer is, yes you can have the same amplitude response with different > phase responses. A simple example is a circuit called an all-pass network. > It has flat frequency response, but the phase response goes from 0° at low > frequencies to 180° at high frequencies. > > Don Borowski > EMC Compliance Engineer > Schweitzer Engineering Labs > Pullman, WA, USA > > From: [email protected] > To: [email protected] > Cc: [email protected], Derek Walton <[email protected]> > Date: 04/19/2011 04:24 PM > Subject: Re: [PSES] LISN Phase angle, why? > Sent by: [email protected] > > I'm left wondering whether any passive network has a unique > amplitude-response for any given phase-response. In other words, can two > or more > phase responses yield identical amplitude response in the frequency > domain. I don't immediately see how that could be true. > _____________________________________ _______________________________________________ > > Ralph McDiarmid | Schneider Electric | Renewable Energies Business | > CANADA | Regulatory Engineer > > From: > [email protected] > To: > [email protected] > Cc: > [email protected], Derek Walton <[email protected]> > Date: > 04/19/2011 03:36 PM > Subject: > Re: [PSES] LISN Phase angle, why? > > I suppose the correct measurements-based answer is to preserve the proper > impulse response. After all, the makers of EMI receivers go through some > trouble to make sure that the IF filters they use are within certain > specified limits for both impulse bandwidth and group delay. Using a LISN > with weird phase characteristics could mess up measurements where you have > > multiple correlated sidebands/harmonics inside the measurement bandwidth. > > Having said that, at least for my (pre-compliance) measurements (150 kHz - > > 30 MHz using 9 kHz IF bandwidth), I think it hardly matters. All I am > seeing are harmonics of the switching power supply frequency, which around > > here are designed to place the fundamental frequency somewhere around 125 > kHz. With this wide spacing of harmonics relative to the measurement > bandwidth, phase and impulse bandwidth don't matter too much. I say 'not > too much' because I do see 120 Hz modulation of the lower order harmonics > as the diodes of the input bridge rectifier turn on and off (I deal almost > > exclusively with low wattage switchers for use in industrial environments, > > thus no harmonic/power factor correction). So there are the 120 Hz > modulation sidebands, and the exact impulse bandwidth and phase probably > do make some difference. Even then I wonder how much they matter when I > turn on the average and quasi-peak detectors, as opposed to what I see > when I do the initial peak measurement. > > Don Borowski > EMC Engineer > Schweitzer Engineering Labs > Pullman, WA, USA > > From: [email protected] - ---------------------------------------------------------------- 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]>
