[email protected] writes: > 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).
Hi Adrian I don't think that this point is a fair comparison, 3458a calibration is only required for absolute measurements which the 720A is incapable of anyway. John > -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. > -- John Devereux _______________________________________________ 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.
