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

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@freenet.de> > An: volt-nuts@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 > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

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@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@freenet.de> > > An: volt-nuts@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 > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

acbern@gmx.de 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" <frank.stellmach@freenet.de> >> An: volt-nuts@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 >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- John Devereux

Hi John, sure, seems I should have been more clear. What I wanted to say is that in order to have traceability starting from just a calibrated 10V (and 10k) standard, which is sufficient to adjust a 3458A, you still need some type of self-calibrating divider to validate the 3458A (which then, once validated, can be your working unit). Or, if one e.g. wants to calibrate a 5440 voltage calibrator from a 10V standard, you also need a divider. Assuming a non-calibrated 3458A, because of its highly linear ADC, can be used transferring the 10V into other voltage ranges, is not valid, the 3458A has a performance validation point that checks (within the testable limits) that the linearity is ok. So no way around a divider unfortunately. In the end, what we talk about is how do we get traceable volts measurement capabilities (to the 10V standard that has been calibrated, if one has a calibrated 1V too (of the 732A or whatever), less work, but the basic problem remains). Adrian > Gesendet: Freitag, 24. April 2015 um 11:43 Uhr > Von: "John Devereux" <john@devereux.me.uk> > An: volt-nuts@febo.com > Betreff: Re: [volt-nuts] Advise to Junior Member Regarding Acquisition of Fluke 5XXX Series Calibrator > > acbern@gmx.de 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 >

Hi Adrian Oh I see... But... I seem to recall the 720A also, similarly, requires linearity validation unless you just "assume" it is inherently linear? The manual shows a test using a second 720A! And that is "only" good to 0.2ppm. John acbern@gmx.de writes: > Hi John, > > sure, seems I should have been more clear. What I wanted to say is > that in order to have traceability starting from just a calibrated 10V > (and 10k) standard, which is sufficient to adjust a 3458A, you still > need some type of self-calibrating divider to validate the 3458A > (which then, once validated, can be your working unit). Or, if one > e.g. wants to calibrate a 5440 voltage calibrator from a 10V standard, > you also need a divider. Assuming a non-calibrated 3458A, because of > its highly linear ADC, can be used transferring the 10V into other > voltage ranges, is not valid, the 3458A has a performance validation > point that checks (within the testable limits) that the linearity is > ok. So no way around a divider unfortunately. > In the end, what we talk about is how do we get traceable volts > measurement capabilities (to the 10V standard that has been > calibrated, if one has a calibrated 1V too (of the 732A or whatever), > less work, but the basic problem remains). > > Adrian > > > >> Gesendet: Freitag, 24. April 2015 um 11:43 Uhr >> Von: "John Devereux" <john@devereux.me.uk> >> An: volt-nuts@febo.com >> Betreff: Re: [volt-nuts] Advise to Junior Member Regarding >> Acquisition of Fluke 5XXX Series Calibrator >> >> acbern@gmx.de 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 >> > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- John Devereux

Hi John, well, if one wanted to use a 720A, only the 0.1 and 0.01 settings are needed, so full linearity check over all decades is not needed. A second 720A to do that is not really precise enough, as the manual also states. But anyway, the preferred divider to use is the 752A. Adrian > Gesendet: Freitag, 24. April 2015 um 16:08 Uhr > Von: "John Devereux" <john@devereux.me.uk> > An: volt-nuts@febo.com > Betreff: Re: [volt-nuts] Advise to Junior Member Regarding Acquisition of Fluke 5XXX Series Calibrator > > > Hi Adrian > > Oh I see... > > But... I seem to recall the 720A also, similarly, requires linearity > validation unless you just "assume" it is inherently linear? > > The manual shows a test using a second 720A! And that is "only" good to > 0.2ppm. > > John > > > > acbern@gmx.de writes: > > > Hi John, > > > > sure, seems I should have been more clear. What I wanted to say is > > that in order to have traceability starting from just a calibrated 10V > > (and 10k) standard, which is sufficient to adjust a 3458A, you still > > need some type of self-calibrating divider to validate the 3458A > > (which then, once validated, can be your working unit). Or, if one > > e.g. wants to calibrate a 5440 voltage calibrator from a 10V standard, > > you also need a divider. Assuming a non-calibrated 3458A, because of > > its highly linear ADC, can be used transferring the 10V into other > > voltage ranges, is not valid, the 3458A has a performance validation > > point that checks (within the testable limits) that the linearity is > > ok. So no way around a divider unfortunately. > > In the end, what we talk about is how do we get traceable volts > > measurement capabilities (to the 10V standard that has been > > calibrated, if one has a calibrated 1V too (of the 732A or whatever), > > less work, but the basic problem remains). > > > > Adrian > > > > > > > >> Gesendet: Freitag, 24. April 2015 um 11:43 Uhr > >> Von: "John Devereux" <john@devereux.me.uk> > >> An: volt-nuts@febo.com > >> Betreff: Re: [volt-nuts] Advise to Junior Member Regarding > >> Acquisition of Fluke 5XXX Series Calibrator > >> > >> acbern@gmx.de 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 > >> > > > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > 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 -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

Stan, Just got this today, so not sure whats going on (seems this was sent on the 24th) and if response is too late, but here it is anyway (hope I understood your problem). I think you are well set with the three instruments you mention, no need for a 720 KVD. say you want to transfer 1v from a 732A (btw: you would actally have the 10V calibrated n this device, as it is more stable) to a 5440A. All you do is measure the 732A 1V output with your 3458A, record the value, connect it to the 5440A and adjust the output voltage until you have the same reading. accuracy is better than the 2ppm, just check the 3458A data sheet. Not sure this answers your question. Adrian > Gesendet: Freitag, 24. April 2015 um 08:04 Uhr > Von: "Stan Katz" <stan.katz.hk@gmail.com> > An: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > Betreff: Re: [volt-nuts] Advise to Junior Member Regarding Acquisition of Fluke 5XXX Series Calibrator > > 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@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@freenet.de> > > > An: volt-nuts@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 > > > _______________________________________________ > > > volt-nuts mailing list -- volt-nuts@febo.com > > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > > and follow the instructions there. > > > > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.