[volt-nuts] Advise to Junior Member Regarding Acquisition of Fluke 5XXX Series Calibrator

[Stan Katz]

Gentlemen,

I concede that:
The need for an HP3458a is imperative.
The need for a Fluke 5440b or better is imperative.
As a minimum, a self constructed Hammon Divider is imperative and will
eliminate the need for a 720a to calibrate cardinal points down to the
100mv level.

However, with my limited metrology knowledge, it appears that a Kelvin
Varley divider is still imperative if one wishes to take a freshly
calibrated/certified 732a or 731b (call it standard "A") 1v "raw"  output
and create 1v +/- 2ppm on a second transfer standard.  If I'm correct, the
only means of converting the raw calibrated 1v output of standard "A" to 1v
+/- 2ppm on standard "B" is to lash up a configuration wherein the KV
divider is set to the reciprocal of the certificate value of the raw 1v on
calibrated "A". I may be somewhat lacking in the precision of my
description so I am including a procedure given in the HP740a manual (see
attached) which accomplishes the above.

Of course, if the primary, or secondary calibration laboratory performs an
*adjustment* on the traveling standard, setting its 1v output to 1v +/-2ppm
(e.g "cooked") the above procedure can be eliminated.  I suspect that
requesting adjustment by a manufacturer, such as Fluke, of a 732a/b would
be only by special arrangement, and probably fetch a fee close to the
purchase price of the instrument.

I hope to hear that I'm wrong, and that the above calibration can be
accomplished without a KV divider.

Stan


On Thu, Apr 23, 2015 at 5:47 PM, <acbern at gmx.de> wrote:

> A few things to keep in mind:
> - the 720A (and the 752A) are self-calibrating, i.e. you can (easily)
> calibrate it yourself before use. The 3458A, using its external artifact
> self-cal procedure based on only 10v and 10k, requires a performance
> verification therafter (at least every second time, see some military docs
> concluding this, I don't recall the link but easy to find; i would actually
> say, to comply with GUM, every time).
> -the linearity of the 3458a is excellent and not beatable up to a 1:10
> ratio, beyond that (e.g. if you want to calibrate an instruments 1000v or
> 100mV range form a 10V reference), it is not usable, again the 720a or 752A
> are superior.
>
> So to summarize, if you want to be selfstanding, and do your calibrations
> with reference to an externally calibarted 10v and 10k resistor only, you
> need a good voltage source (5440 is hard to beat even by the 5720A, and can
> replace, with some compromises, also a 732a if need be), a 3458A but also
> some type of self-cal 1:10 and 1:100 divider (720A or 752 or similar). You
> could build a hammon divider (1:10 and 1:100) yourself, for much less than
> a 720A costs, and since it is self-cal, if you do it right, you do not need
> to compromise on accuracy. what you really need is just the decade divide
> ratios to do all the 3458A validation, and then go from there. all the
> gazillion other ratios that the 720a offers are really not needed then.
>
> Adrian
>
>
>
> > Gesendet: Donnerstag, 23. April 2015 um 21:19 Uhr
> > Von: "Frank Stellmach" <frank.stellmach at freenet.de>
> > An: volt-nuts at febo.com
> > Betreff: [volt-nuts] Advise to Junior Member Regarding Acquisition of
> Fluke   5XXX Series Calibrator
> >
> > Hi Stan,
> >
> > the 720A can easily be replaced by an HP3458A, which is superior to the
> > KV divider in several aspects.
> >
> > First, the 3458A has 3-10 times better linearity, 0.02ppm (typ.) of F.S.
> > compared to 0.1ppm of input for the 720A.
> > Therefore, a 10:1 transfer is accurate to 1ppm for the 720A only,
> > whereas the 3458A manages 0.1 to 0.3 ppm.
> >
> > The self calibration is much easier on the 3458A, as are all these
> > calibration measurements, you mentioned.
> > (Fluke has published a good application note, how to replace their own
> > old style equipment as KV, Null VM, etc. by their own 8 1/2 digit 8508A).
> >
> > And you may get a very reasonable and recent instruments for 3000$/€,
> > maybe much less for older ones.
> >
> >
> > A calibrator is limited in use, as it needs a Null VM at least.
> >
> > Anyhow, I recommend the Fluke 5440A / 5442A DCV calibrators.
> >
> > They are ultra stable, having 2 stacked SZ263A references inside, good
> > for 732A stability.
> >
> > Their D/A is also extremely linear, I measured something like 0.2ppm INL
> > against my 3458A, and they are spec'd to 0.5ppm of output, also superior
> > to the 720A in some volt areas.
> >
> > They also have this handy autocal function (like the 3458A) for the 4
> > higher volt ranges ( 11, 22, 220, 1000V),  once that they are externally
> > calibrated, and because their internal component drift is low, after
> > these years.
> > That means, as their internal reference is very stable, you may bring it
> > near 24hr. specification, every time you do the autocal.
> > I could not measure any deviation to that, using my 3458A, plus a self
> > built precision Hammon divider for 1kV.
> >
> > Their autocal feature is not explicitely promoted, but you will find
> > that description "between the lines" in the addendum of the user manual.
> >
> > Only the 1V and 100mV range have to be externally calibrated quite often.
> >
> > These instruments may cost about 2000$/€.
> >
> > So you better have both, the 5440 and the 3458A.
> >
> > Frank
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