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?
> From: John Woodgate <[email protected]> > Reply-To: John Woodgate <[email protected]> > Date: Thu, 18 Dec 2003 22:58:02 +0000 > To: [email protected] > Subject: Re: CISPR 25 Conducted Emissions (Current Method) > > > I read in !emc-pstc that [email protected] wrote (in > <of227b3f0b.4367e65e-on85256e00.0056b9fa-85256e00.0056d...@jci.com>) > about 'CISPR 25 Conducted Emissions (Current Method)' on Thu, 18 Dec > 2003: >> Please read the attached document that he assembled for the details. > > Not relevant to the question, but I'm very disappointed to see > 'dB(ohm)'. The point is that this concept is mathematically nonsense. > > Consider V = IR > > 20logV = 20log(IR) = 20log I + 20log R > > Now consider > > P = I^2R > > 10logP = 10log(I^2) + 10logR > > So is the 'dB(ohm)' 20logR or 10logR? > > The UK national EMC committee has pointed this out to CISPR committees > on several occasions, but the mistake keeps being made. > -- > 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
