For myself, I have found it a whole lot less confusing to work in voltage
and current as linear units, then at the end converting back to dB if
necessary.
Don Borowski
Schweitzer Engineering Labs
Pullman, WA
Ken Javor <[email protected]> wrote on 12/18/2003 05:22:55 PM:
>
> 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!
> >
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