[volt-nuts] AC calibration

[Dave M]

Well, you sort of answered your own question.  The equipment is called a 
Thermal Transfer Standard, but instead of thermistors, it uses a 
thermocouple.  Look at the manual for the Fluke 540B 
(http://bama.edebris.com/manuals/fluke/540b/) and you'll see how it's done.
Basically, the AC source is input into the transfer standard, and the 
standard's internal reference voltage is adjusted for a null on the 
galvanometer.  Leaving the reference voltage setting alone, a DC voltage is 
input into the unit, and the DC source is adjusted for a null on the 
galvanometer.  At that point, the AC voltage source is equal to that of the 
DC voltage source.

Ther are thermocouple-type thermal converters used for RF voltage 
measurements with the transfer standard.  They aren't cheap, and you have to 
have a converter for each range of voltages that you need to measure.  The 
thermal converters used with this type of transfer standard isn't great (50 
MHz or so typical), but their accuracy far surpasses that of the thermistor 
type sensors.

There are other brands and models of thermal transfer standards, but I have 
a Fluke model 540 and a few thermal converters.  That's why I referred you 
to the manual for it.

Cheers,
Dave M


pa4tim at gmail.com wrote:
> Is there a way to link an AC voltage to a DC source for compare. I
> can check my calibrators (like a Fluke 332, 760 , 731 and a Philips)
> against standardcells. But for AC I can not do that. I have two AC+DC
> TRMS 7,5 digit meters but the last calibration was 2 years ago.
>
> My idea is in theory simple. It is based on the thermal converters
> used in RF powermeters. Two resistors, two high resolution
> temperature meters. AC on the first en DC on the second. If both are
> the same temperature the AC voltage is the same as the DC voltage.
> But I'm sure some people here have done this in the past. I would
> like to use it for 50 to 100 kHz (or less) and something like for 1V,
> 10V and 100V (and use several resistors/heaters.)
>
> Or mabey there is an other way to convert AC (for RF it can be done
> with lightbubs but I never tryed that)  I do not mind if it is slow
> etc, I like this sort of experiments. You can learn a lot from it.
>
> Fred, pa4tim