Works for me. > From: John Woodgate <[email protected]> > Reply-To: John Woodgate <[email protected]> > Date: Fri, 19 Dec 2003 13:29:14 +0000 > To: [email protected] > Subject: Re: CISPR 25 Conducted Emissions (Current Method) > > > I read in !emc-pstc that Ken Javor <[email protected]> wrote > (in <bc07af0f.88f0%[email protected]>) about 'CISPR 25 > Conducted Emissions (Current Method)' on Thu, 18 Dec 2003: > >> It is true that the unit dB Ohm has to be interpreted in context. >> However that does not change its utility. Current probe transfer >> impedance and shielding transfer impedance both have units of dB Ohm. >> What would be a better substitute? > > Decibels ref 1 volt per amp would be unambiguous and mathematically > defensible. Abbreviation dB(V/A). This also has the advantage that the > abbreviation immediately explains what the quantity means. If I see a > current probe transfer impedance expressed as '20 dB(ohm)', I'm not sure > what that means, but if its '20dB(V/A)', then I know immediately that 1 > A through it gives 10 V out. Similarly for shield transfer impedance. I > can see straight away that 100 mA of shield current gives 1 V from end > to end (poor shield or a very long cable!). > > Formally, the decibel is a power ratio, so P = I^2R applies and thus the > only possible legitimate 'dB(ohm)' is 10logR. But that is hardly ever > what it means in these EMC standards. > -- > Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk > Interested in professional sound reinforcement and distribution? Then go to > http://www.isce.org.uk > PLEASE do NOT copy news posts to me by E-MAIL! > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ieee-pses.org/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [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: > 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.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc
