What are 6.5 Digit Multimeters Good For?
in [Design]
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From: D from BC on 11 Mar 2010 22:11 In article <hnc95i$82b$1(a)news.eternal-september.org>, Jon_Slaughter(a)Hotmail.com says... > > John Larkin wrote: > > On Thu, 11 Mar 2010 17:56:35 -0800, D from BC > > <myrealaddress(a)comic.com> wrote: > > > >> 6.5 digit multimeters sell around $1000.00. > >> For electronics development, are these $1000 multimeters really > >> necessary? > >> What are they good for? > > > > Measuring to PPM accuracy, and measuring microvolt-level voltages. And > > as a traceable standard for calibrating products. > > > > The Fluke 8845A is excellent. > > > > John > > What's the big deal? Can't they just switch to 24-bit ADC's on the cheap and > get the accuracy? Or is there some special techniques required to get that > resolution in practice? It's probably trouble to push the noise floor down with the front end electronics in the multimeter. 32 ADC http://focus.ti.com/lit/ds/symlink/ads1282.pdf $77 at Digikey I think that's 10 digit. 2^32 = 4294967296 Say full scale is 1V then 1st step is 232picovolts. uhuh.. I get 1mV fuzz just by shorting out my scope probe!
From: Jon Slaughter on 11 Mar 2010 23:06 Jon Kirwan wrote: > On Thu, 11 Mar 2010 20:33:16 -0600, "Jon Slaughter" > <Jon_Slaughter(a)Hotmail.com> wrote: > >> John Larkin wrote: >>> On Thu, 11 Mar 2010 17:56:35 -0800, D from BC >>> <myrealaddress(a)comic.com> wrote: >>> >>>> 6.5 digit multimeters sell around $1000.00. >>>> For electronics development, are these $1000 multimeters really >>>> necessary? >>>> What are they good for? >>> >>> Measuring to PPM accuracy, and measuring microvolt-level voltages. >>> And as a traceable standard for calibrating products. >>> >>> The Fluke 8845A is excellent. >>> >>> John >> >> What's the big deal? Can't they just switch to 24-bit ADC's on the >> cheap and get the accuracy? Or is there some special techniques >> required to get that resolution in practice? > > Measurement precision and accuracy aren't the same. You mix > "resolution," "accuracy," and "24-bit" in the same breath. > Your a freaken genius!
From: Jon Slaughter on 11 Mar 2010 23:16 D from BC wrote: > In article <hnc95i$82b$1(a)news.eternal-september.org>, > Jon_Slaughter(a)Hotmail.com says... >> >> John Larkin wrote: >>> On Thu, 11 Mar 2010 17:56:35 -0800, D from BC >>> <myrealaddress(a)comic.com> wrote: >>> >>>> 6.5 digit multimeters sell around $1000.00. >>>> For electronics development, are these $1000 multimeters really >>>> necessary? >>>> What are they good for? >>> >>> Measuring to PPM accuracy, and measuring microvolt-level voltages. >>> And as a traceable standard for calibrating products. >>> >>> The Fluke 8845A is excellent. >>> >>> John >> >> What's the big deal? Can't they just switch to 24-bit ADC's on the >> cheap and get the accuracy? Or is there some special techniques >> required to get that resolution in practice? > > It's probably trouble to push the noise floor down with the front end > electronics in the multimeter. I read that this is not difficult by paralleling ADC's or using averaging. Since the noise generally is symmetric(generally gaussian) by averaging it will cancel out. I guess it is more important that the ADC be stable but as long as any fluxuations are symmetric(such as clock jitter) then averaging should take care of most of the problems. > 32 ADC > http://focus.ti.com/lit/ds/symlink/ads1282.pdf > $77 at Digikey > I think that's 10 digit. 2^32 = 4294967296 > Say full scale is 1V then 1st step is 232picovolts. > uhuh.. > I get 1mV fuzz just by shorting out my scope probe! Yes, but maybe that is due to the scope not using that 32-bit ADC? ;)
From: John Larkin on 11 Mar 2010 23:30 On Thu, 11 Mar 2010 20:33:16 -0600, "Jon Slaughter" <Jon_Slaughter(a)Hotmail.com> wrote: >John Larkin wrote: >> On Thu, 11 Mar 2010 17:56:35 -0800, D from BC >> <myrealaddress(a)comic.com> wrote: >> >>> 6.5 digit multimeters sell around $1000.00. >>> For electronics development, are these $1000 multimeters really >>> necessary? >>> What are they good for? >> >> Measuring to PPM accuracy, and measuring microvolt-level voltages. And >> as a traceable standard for calibrating products. >> >> The Fluke 8845A is excellent. >> >> John > >What's the big deal? Can't they just switch to 24-bit ADC's on the cheap and >get the accuracy? Or is there some special techniques required to get that >resolution in practice? Who is "they"? An ADC needs a voltage reference and, generally, front-end differential amplifiers, filters, and attenuators. And to be a DVM, it needs a user interface, a display, and a data interface. Oh, power supplies too. If it does AC and ohms, it needs more stuff. John
From: Jim Yanik on 12 Mar 2010 00:25
D from BC <myrealaddress(a)comic.com> wrote in news:MPG.26034c831878edc69896e6(a)209.197.12.12: > In article <a69jp59q5nvmomn6rqobm4q4a3m0a4088k(a)4ax.com>, > jjlarkin(a)highNOTlandTHIStechnologyPART.com says... >> >> On Thu, 11 Mar 2010 17:56:35 -0800, D from BC >> <myrealaddress(a)comic.com> wrote: >> >> >6.5 digit multimeters sell around $1000.00. >> >For electronics development, are these $1000 multimeters really >> >necessary? >> >What are they good for? >> >> Measuring to PPM accuracy, and measuring microvolt-level voltages. And >> as a traceable standard for calibrating products. and they generally have better AC volt accuracies. >> >> The Fluke 8845A is excellent. the HP/Agilent 14401A is better. :-) >> >> John > > Ah.. the tool that sets the tools. > > Of course there's always something better.. :P > 8.5 Digit multimeter > http://www.home.agilent.com/agilent/product.jspx?nid=- > 536902435.536881781.00&cc=US&lc=eng > it's not how many digits in the display,it's how ACCURATE the meter is that matters. -- Jim Yanik jyanik at localnet dot com |