[time-nuts] OT: AC voltage standard

WB6BNQ wb6bnq at cox.net
Tue Nov 6 13:08:51 EST 2007

To All,

Let me repeat what John De Armond stated.  It is most important.

A "standard cell," whether saturated or unsaturated, cannot be loaded under any
circumstances.  Any current draw will upset the cell chemistry and cause the cell
to change value and the odds are it will never return to its previous value.
Even with a 10 megohm load.

If you can come by any reasonable thermocouple made for measuring AC, even a
so-called RF amp meter, then you could, using a good deal of caution, apply an AC
signal and then apply a DC voltage to come to the same level.  Remember to feed
the DC voltage both ways to account for the "reversal" error in the thermocouple.

If you want to do the Flip-Flop reversal process then use a very well regulated
DC source.  This method was used by Tektronix in their older tube type
oscilloscopes.  Their method of calibrating that function of the scope was to
pull a tube out and set the DC voltage to some predetermined level.  He exact
procedure escapes me at the moment.

Within the ability of your EYE to see the same point, you could just use a scope
and compare the line shift using a DC source adjusted to the same level of the AC
signal on the scope screen.  With careful comparison you could do a little better
then 3 %.  That may be all you need to "check" yourself for sanity.

An old, used and tired EX-metrologist

Joe McElvenney wrote:

> Hi,
> Excuse the topic but is does push the same buttons as it were.
> After calibrating my old HP54502A 6-bit digitizing scope I'm left
> with an error I can't quite believe and so am trying to determine
> which of my instruments is telling me lies.
> Anyone know of a simple way of producing an AC voltage standard
> suitable for general workshop use without reference to another
> one? About one percent would be good enough, wave shape and
> frequency accuracy not important (wash my mouth out). I have a
> Weston Cell for DC voltage calibration, a Rb one for frequency but
> nothing for AC volts. Perhaps there is a chip out there that
> clocks between accurate limits that I could use as a source?
> Thanks - Joe
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