Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the time constant of a CISPR filter on the spectrum analyzer. - connection to the source makes a big difference. I assume when you calibrated the reading with a sine wave, a coaxial cable with coax connectors at both ends was used. Presumably the product does not have a coaxial connector on the Vcc plane, so you have to make your own connection or use a hand-held probe. This is very extra noise usually gets in the path, and the scope reading becomes unrealistically high. I have found no active scope probes so far, which would give a correct reading in a noisy environment. We hopefully should not see noise on the Vcc planes more than a few hundred mV. In contrast, many scope probes can pick up spikes as big as volts from the environment. If you want to measure noise levels below 100mVpp, double-shielded coax is necessary in noisy environments. Here the 'noisy environment' refers to the close vicinity of the point you test. The simplest test is: take your present probe, and hook up a good double-shielded coax to the same points. Check both readings on the same scope at the same time, and compare.
I hope this helps. Best regards, Istvan Novak SUN Microsystems From: "Charles Grasso" <cgrassospri...@earthlink.net> To: "Ken Javor" <ken.ja...@emccompliance.com>; "Emc-Pstc" <emc-p...@ieee.org> Sent: Saturday, July 26, 2003 9:11 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser > > Hi all, > > Actually I was using a good ole Spectrim Analyser > so I sidestepped the windowing issue/software issues > altogether. > > What I was(am)trying to do was match the max voltage > as measured on a scope with the value as measured > on a SA. > > I first calibrated myslef using a known source - a sine wave. > The amplitudes fell in just as theory predicted. Encouraged, > I then probed the Vcc plane on a product I was working on > and was not so happy!! > > Any ideas? > > -----Original Message----- > From: Ken Javor [mailto:ken.ja...@emccompliance.com] > Sent: Saturday, July 26, 2003 4:19 PM > To: Charles Grasso; Emc-Pstc > Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser > > > I presented a paper on that very subject about a decade ago at one of the > EMC T&D magazine EMC symposia. I used a Fluke Scopemeter and some FFT > software that came with it. The Fluke interfaced to the PC through an > optically isolated RS-232 protocol. It worked quite well from a > pre-compliance or troubleshooting point-of-view. You could use time > windowing to separate the signals deriving from leading and falling edges > from the signals deriving from the pulse itself. I used LISNMATE and > LISNMARK mode separation devices to show that the rising/falling edge > signals were common mode, while the pulse itself generated differential mode > signals. > > > From: "Charles Grasso" <cgrassospri...@earthlink.net> > > Reply-To: "Charles Grasso" <cgrassospri...@earthlink.net> > > Date: Sat, 26 Jul 2003 16:18:36 -0700 > > To: "Emc-Pstc" <emc-p...@ieee.org> > > Subject: Q on Correlation of Votage ripple with a Spectrum Analyser > > > > > > Hi All, > > > > > > Has anyone tried correlating the voltage ripple > > as seen on a scope with the amplitudes measured > > on a Spectrum Analyser? > > > > I tried doing that the other day with ..umm. minimal > > success. I think that due to the comples convoltions > > that would have to occur when FFT'ing an irregular > > voltage shape. > > > > Charles Grasso > > Echostar Communications. > > > > ------------------------------------------- > > 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: emc_p...@symbol.com > > > > For policy questions, send mail to: > > Richard Nute: ri...@ieee.org > > Jim Bacher: j.bac...@ieee.org > > > > Archive is being moved, we will announce when it is back on-line. > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > > > > ------------------------------------------- > 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: emc_p...@symbol.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > 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: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
