I don't believe Ed was wrong at all, in most any case I can think of he was precisely correct. Whether you use 10 log () or 20 log () depends upon whether the ratio that is the argument of the log function is power or something related to power by a square-law relationship. The most obvious of these are voltage and current. But when impedance is used to get from a voltage to a current or vice versa, then the basic equation is V = IR and since both V & I are 20 log quantities, impedance must be as well. Hence any equation in which capacitance or inductance are used to get at reactances must also follow a 20 log dependency. This is the basis of impedance paper, and also any of you who have ever used a current probe characterized by transfer impedance also know that the impedance of the probe in dB Ohms is 20 log (Impedance in Ohms).
on 6/27/02 9:54 AM, Price, Ed at ed.pr...@cubic.com wrote: > > I proposed the capacitance unit of dBF with tongue firmly planted in cheek. > And yes, maybe 10 Log is more proper than 20 Log (hey, 44.5 dB error is as > close as I get sometimes). > > OTOH, the more I think about it, resistance, inductance and capacitance > values in practical circuitry exist over such a wide numeric range that > perhaps a logarithmic scale would be appropriate. 470 k Ohms, 0.47 M Ohms, > 470,000 Ohms are all 113 db Ohm. > > Not to mention that the US national debt is currently only about 128 dB$ > (yes, I did use 10 Log here, because everyone agrees that money is power) > at: > http://www.brillig.com/debt_clock/ > > Ed > > > Ed Price > ed.pr...@cubic.com > Electromagnetic Compatibility Lab > Cubic Defense Systems > San Diego, CA USA > 858-505-2780 (Voice) > 858-505-1583 (Fax) > Military & Avionics EMC Services Is Our Specialty > Shake-Bake-Shock - Metrology - Reliability Analysis > > > >> -----Original Message----- >> From: Wan Juang Foo [mailto:f...@np.edu.sg] >> Sent: Wednesday, June 26, 2002 7:00 PM >> To: emc-p...@majordomo.ieee.org >> Subject: RE: case of units >> >> >> >> >> Dear all, >> >> I wonder if dBF is 20 log C or 10 log C ? >> >> My personal guess is that if VA= V² Z and Z=sC then I suppose >> dBF should >> carry a 10 log tag. Could Ed be 44.5 dB off the mark? >> Just my 2 ¢ worth. (On an aside, I must say this hidden >> character thingy >> is rather fascinating , cents is [Num Lock] <Alt-0162>) >> :-) >> Tim Foo >> >> > SNIP >> >>> -----Original Message----- >>> From: Nick Rouse [mailto:nick.ro...@btopenworld.com] >>> Sent: Wednesday, June 26, 2002 1:14 PM >>> To: emc >>> Subject: Re:case of units >> <snip> >>> Millifarad sized capacitors are now common >>> and I have seen one instance of one marked mF. >>> With the new double layer supercaps multifarad >>> rated capacitors are also available and >>> someone is marketing a 28kF capacitor >>> or if you prefer 0.028MF >>> >>> Nick Rouse >>> >> >> >> Wow, an 89 dBF capacitor! >> >> ED >> <snip> >> > > ------------------------------------------- > 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: davehe...@attbi.com > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > -- Ken Javor EMC Compliance Huntsville, Alabama 256/650-5261 ------------------------------------------- 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: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
