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, <[email protected]> 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" <[email protected]> > > An: [email protected] > > 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 > > _______________________________________________ > > volt-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >
2ppmtransfer.pdf
Description: Adobe PDF document
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