[SI-LIST] Re: How they measure true RMS
- From: Juergen Hannappel <hannappe@xxxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 17 Dec 2003 16:31:27 +0100
Paul Levin <levinpa@xxxxxxxxxxxxx> writes:
> Dear Andrew,
>
> Perhaps you are thinking of the watt meter style. I still own a Weston
> meter that has the voltage applied to the field coil and a sample of
> the current (i.e., voltage across a shunt resistor) going through the
> moving coil. In this way, the deflection is proportional to the
I always thought it was the other way round, i.e. moving voltage coil
and static current coil, which would be more useful as for small
currents the need for a shunt goes away.
> average value of volts x amps. If you were to apply the voltage to
> both coils (through appropriate scaling factors, of course,) then the
> reading would be the average value of volts x volts, or RMS voltage.
Only MS voltage, because you don't get the R(oot)
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto:hannappel@xxxxxxxxxxxxxxxxxx Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23
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