On Mar 12, 9:05*pm, " wrote:
On Mar 12, 2:02*pm, "Josepi" wrote:

Careful. Variacs are known waveform distorters. The government would not let
us use them for precision power measurements as the waveform adopts many
harmonics in some units.

Which brings up a couple of points. *The temperature of the filament
in vacuum tubes does vary if you have AC applied to it. *So you will
get some distortion from that. *But most of the better DVM's are true
RMS meters, at least on Voltage. * I would suspect they would also
measure true RMS current. *But does anyone know for sure?

* * * * * * * * * * * * * * * * * * * * * * * *Dan

This says they do:
http://www.newportelect.com/manuals/ACGUIDE.htm

I think the RMS converter is after the current shunt that turns
current into voltage.

jsw