[volt-nuts] Dial-a-vider

[Charles Steinmetz]

Joe wrote:

>I know someone who has a General Resistance Dial-a-vider DV-4107   *   *   *
>
>The reason I'm interested in this is not so much for use with a DC
>reference, as I already have the VS330. I was thinking about using it for
>AC, if I can buy or make a reasonably accurate AC reference.

It's a basic 7-decade DC Kelvin-Varley divider.  The Fluke 720A is 
generally considered best-of-breed, both for its high quality and its 
self-calibration features.  To my knowledge, no manufacturer of these 
DC dividers rated them for AC use, and they were not generally built 
with non-inductive resistors.  So it might work OK at very low 
frequenceis, but everything you did with it would be an "off-label" 
application.  Furthermore, the 100k ohm input resistance demands an 
ultra-high resistance (impedance) load -- it is designed to be used 
with a DC null meter.  But there is no ultra-high impedance AC null 
meter, and if there were, stray fields of every sort would wreak 
havoc on any measurement you tried to make with it.

For accurate AC measurements or calibration, metrologists use a 
"thermal transfer standard" (or "AC/DC transfer standard"), in 
conjunction with an AC source and an accurate DC source.  See:

<http://download.flukecal.com/secure/792A____imeng0100.pdf?nvb=20130811035444&nva=20130811040944&token=0aa649a8db6274c6ae587>


Best regards,

Charles