In terms of power change in the system as a fuction of resistance (or scalor of impedance), then I expect it should be 10logR "dB(Ohms)"
Why not use dB(ohms) if dB(V) is considered a valid unit? Ralph McDiarmid, AScT Compliance Engineering Group Xantrex Technology Inc. From: John Woodgate [mailto:[email protected]] Sent: December 18, 2003 2:58 PM 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
