What are 6.5 Digit Multimeters Good For?
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From: D from BC on 12 Mar 2010 03:05 In article <kisjp5h1mmb1du7r5b37m07g8dcdbfq6ja(a)4ax.com>, OneBigLever(a)InfiniteSeries.Org says... > > On Thu, 11 Mar 2010 19:11:54 -0800, D from BC <myrealaddress(a)comic.com> > wrote: > > >I get 1mV fuzz just by shorting out my scope probe! > > > But have no clue as to why. That wasn't worth reading.
From: D from BC on 12 Mar 2010 03:10 In article <kisjp5h1mmb1du7r5b37m07g8dcdbfq6ja(a)4ax.com>, OneBigLever(a)InfiniteSeries.Org says... > > On Thu, 11 Mar 2010 19:11:54 -0800, D from BC <myrealaddress(a)comic.com> > wrote: > > >I get 1mV fuzz just by shorting out my scope probe! > > > But have no clue as to why. Want to explain it for me?
From: Archimedes' Lever on 12 Mar 2010 04:02 On Fri, 12 Mar 2010 00:05:48 -0800, D from BC <myrealaddress(a)comic.com> wrote: >In article <kisjp5h1mmb1du7r5b37m07g8dcdbfq6ja(a)4ax.com>, >OneBigLever(a)InfiniteSeries.Org says... >> >> On Thu, 11 Mar 2010 19:11:54 -0800, D from BC <myrealaddress(a)comic.com> >> wrote: >> >> >I get 1mV fuzz just by shorting out my scope probe! >> >> >> But have no clue as to why. > >That wasn't worth reading. The one millivolt, or the lack of a clue?
From: Fred Bartoli on 12 Mar 2010 04:57 Jon Kirwan a �crit : > 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. > > Jon If only that... -- Thanks, Fred.
From: Martin Brown on 12 Mar 2010 05:18
D from BC wrote: > 6.5 digit multimeters sell around $1000.00. > For electronics development, are these $1000 multimeters really > necessary? Depends what you are doing. In the 80's the kit I worked on used a bank of up to 8 Solartron 7060 DVMs to measure signals to ppm accuracy. Most people settled for 4 or 6 and there was an option to have just one DVM and multiplex the signals. We changed from Solartrons to the first high precision ADCs that were able to achieve the required precision in the early 90's, but a few 7060s (and their improved replacements) were needed for test and calibration. The new kit had to be provably better than the 7060 on the bench before the punters would even consider it. These days high precision DVMs tend to be used mostly to calibrate, test and correct the linearity, drift of secondary measurement devices and sensors. I can't imagine anyone building high precision DVMs into commercial kit today but I could be wrong. We stopped doing it in the early 90's. I can't remember the chip number but I think it was an AD part with dual slope integration and almost ppm accuracy out of the box. I did the calibration software to correct systematic errors and linearise it for our application. Obtaining true linearity is harder than it sounds. Integration periods had to be local mains synchronous and the linearity had to be spot on for the intended application to work at all. Users were looking for reproducible 4-5 figure accuracy on the ratio of feeble ion beam signals from Faraday detectors. Dating moon rocks and similar. > What are they good for? Things where you need excellent long term stability and linearity with genuine 6 digit accuracy after signals are averaged for long enough. Regards, Martin Brown |