[volt-nuts] AC Voltage Measurement Standards

Fri Jul 11 09:25:28 EDT 2014

Fellow Volt Nuts,

The ultimate standard of AC Voltage is still primary sets of Thermal
Converters that are characterised in terms of their thermal models and the
modelled lumped elements ( inductive and capacitance effects). The
programmable AC JJA's are very stable and reproducible AC sources cannot be
primary references in themselves because their frequency response (although
modelled) is still calibrated against other standards mostly TVC's.

To those who have requested a copy of the paper on calibrating thermal
converters against other converters please be patient and I will try and get
my response over the weekend.

Kind Regards,

Stephen Grady
Sydney Australia

-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Tom Knox
Sent: Friday, 11 July 2014 9:47 AM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] AC Voltage Measurement Standards

The ultimate AC standard would be NIST's AC Josephson junction array. Sam
Benz and his team continue to make advances, pushing the accuracy and output
level. They have also substantially reduced the needed electronics placing
much of the peripheral electronics in a custom built two-U enclosure. NIST
has also recently introduced a fully programmable JJA that automates most of
the set up and operation. It won't be long before we need 10 1/2 digit DMM's
Cheers; Thomas Knox

> From: acbern at gmx.de
> To: volt-nuts at febo.com
> Date: Fri, 11 Jul 2014 01:13:44 +0200
> Subject: Re: [volt-nuts] AC Voltage Measurement Standards
> 
> in a nutshell, what i am doing is that I first establish the dc (+/-)
output of the ref. TVC at nominal and then determine the ac voltage from a
precision, highly linear (datron 4808) ac source that generates that default
output voltage at the key frequencies. that establishes a set of ac voltage
settings. for these the deviations of the TVC are known from the
calibration. then I do the same with the TVC to be calibrated. (factor of 2
nom. voltage is important to stay within allowable range). that way you can
link both.
> sure, sending all to cal is more precise, if you get the right lab at
least, but also very expensive.
> 
> would sure be interested in your tech paper
> 
> 
> 
> > Gesendet: Donnerstag, 10. Juli 2014 um 13:27 Uhr
> > Von: "Stephen Grady" <grady.steve at gmail.com>
> > An: "'Discussion of precise voltage measurement'" <volt-nuts at febo.com>
> > Betreff: Re: [volt-nuts] AC Voltage Measurement Standards
> >
> > Todd and anyone else would is interested,
> > 
> > Measuring a Thermal Converter against another Thermal Converter is a bit
of
> > a black art. The main problem is thermal converters are a square law
device
> > that is if you change the input voltage by a factor of 2 the output
voltage
> > will change by a factor of approximately 4. Now I say approximately
because
> > for most thermal converters like the Fluke 540B, A55, Ballantine and
Holts
> > the actual factor can be anywhere from 1.4 to 1.8 due to losses in the
> > thermal converter. In the literature you often see this factor refer to
as
> > the N factors. Each thermal converter will have its own N factor which
must
> > be measured to make sense of the measurements.
> > 
> > It even becomes more difficult in that the AC-DC difference of a thermal
> > converter is defined as (Vac-Vdc)/Vdc where Vac and Vdc are the inputs
to a
> > thermal converter which give an equal output from the converter. Also
Vdc is
> > the mean of the forward and reverse DC voltages. The problem is that
when
> > you have two converters connected in parallel you cannot balance both
> > converters AC and DC inputs to produce equal voltage out of the
converters
> > at the same time because each converter has its own AC-DC difference and
its
> > own N factor.
> > 
> > It anyone is interested I can send them a technical paper that describes
> > this process and the appropriate math to use but I cannot send it to the
> > list due to copyright issues.
> > 
> > Kind Regards,
> > 
> > Stephen Grady
> > Sydney Australia
> > 
> > 
> > -----Original Message-----
> > From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
> > Behalf Of Todd Micallef
> > Sent: Thursday, 10 July 2014 2:36 AM
> > To: Discussion of precise voltage measurement
> > Subject: Re: [volt-nuts] AC Voltage Measurement Standards
> > 
> > I would like to know more about your setup. Which source(s) are you
using
> > for the input and which nanovoltmeter(s) are you using to transfer the
10V
> > TVC to your other converters? I remember you asking on PMEL forum about
the
> > accuracy of using a 34420A nanovoltmeter. I did not see a response as to
> > whether you opted for an alternative like Keithley 2182(A) or a low
noise
> > preamplifier connected to a 3458A.
> > 
> > I have done some reading about how NIST transfers their calibrations
using
> > two TVC's in parallel and I am guessing that is what you are doing.
> > 
> > http://www.nist.gov/pml/div684/acdc/tcs.cfm
> > 
> > To transfer the accuracy up/down to other TVC's at different rated
voltages
> > appears to be a difficult task since they typically need at least half
the
> > rated max voltage to be within spec. It would be similar to starting
with a
> > SR104 standard and transferring its value through a set of SR1010 and
> > SR1050 resistors using an ESI 242.
> > 
> > I have a few AC sources, and I would like to be able to verify my TVC's
> > without sending all of them out for cal. Ballantine quoted $600+ per TVC
and
> > I haven't checked what Fluke would charge for each A55.
> > 
> > Todd
> > 
> > 
> > I personally did the following: I got a Ballantine 1605A transfer
> > > voltmeter. This is comparable to the 792A in a way, except it was much

> > > cheaper. It is automatic, much easier to use than the Fluke 540 and 
> > > goes up to I think 100MHz. This can be used for percision calibrations

> > > as a working standard. The calibration of this meter as well as others

> > > (e.g. the 3458A in its AC mode) I am doing with a set of thermal
> > converters (0.5V to 100V).
> > > One of which (10V) has been externally calibrated up to 30MHz, cal of 
> > > the others are derived from it. That way I am deriving everything from

> > > a very precisely (few ppm) calibrated 10V TVC. Overall, this saves 
> > > cost on the calibration side, allows for high accuracy and measurement
> > speed is good.
> > >
> > >
> > >
> > >
> > >
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