9½ Digit Multimeter, feasible?

[dietert1]

I think there will be a step forward as soon as somebody makes a low noise, completely ovenized meter, similar to the Z10. I mean with constant temperature, humidity and pressure.
Nowadays we have those nice integrated sensors that didn't exist when the 3458A was designed. E.g. the Bosch BME680 sensor is specified with RMS noise of 0.12 Pa, equiv. to 1.7 cm height change! And when using those sensors inside an oven, they perform really well. My latest setup delivers relative humidity readings predictable to +/- 0.1 % over several weeks.
Also Peltier elements became a mainstream product. So we can have cooling without moving air. Tremendous progress has also been made with low power, yet fast programmable logic (cellular phone technology). It may take some more time, but sooner or later people will come up with something much better than a 3458A.

Regards, Dieter

[iMo]

Creating a super stable controlled environment (like temperature, pressure, humidity, emi, radiation, etc) is an essential prerequisite, indeed, but will not help much, imho. You have to come with entirely new devices, based on ie. sub nanometer technology, or new material's physics, etc.

[dietert1]

Creating a super stable controlled environment (like temperature, pressure, humidity, emi, radiation, etc) is an essential prerequisite, indeed, but will not help much, imho. You have to come with entirely new devices, based on ie. sub nanometer technology, or new material's physics, etc.

I don't have to. In my opinion there has been enough new technology to try and do better.

[nimish]

You also need a stable voltage source under test to measure.

Which... exists (a JJ). I always wondered what exact measuring system gets employed to evaluate a JJ. Or maybe it's always the physics behind it warranting the output and the data never "flows in that direction."

The Josephson effect is exact, so all you need is a precise enough time/frequency standard (easy). High speed serdes have made ultra stable time sources dirt cheap too.

[BrianHG]

8.5 digit meters already messes with my brain....
  9.5 digit?   What do you want me to do with that? 

It like trying to measure a 1k weight down down below the nano-gram, down to the pico-gram range.

I'm sure the moon orbiting above will mess with your measurements.

[Kleinstein]

.... I always wondered what exact measuring system gets employed to evaluate a JJ. Or maybe it's always the physics behind it warranting the output and the data never "flows in that direction."

The JJ is used for the definition and is thus exact. For evaluation before using it as the primary standard they still had to carefully check it against to old standards. Another test is checking 2 different JJ sources against each other. This was done with no detectable difference in the voltage, and they really looked hard. With a superconducting cicuit one can get very high accuracy, as there is not thermal EMF with superconductors. So no issue comparing mV voltages to the sub ppb level.

The actual use cases for a 9 digit DMM would be limited, mainly metrology and maybe a very few science experiments.  Anyway current 8 digit meters are not really accurate to the 8 th digit, it is just the noise and short time stabilty so that the 8the digit makes some sense. The stability and linearity are more good at the 7 th digit (or even worse with some types). One kind of needs the better noise to check the stability and linearity. The difficuly in making a much better meter is also more with the linearity and stability, not so much the noise.

[iMo]

Almost everybody plays with JJ these days.. 

[dietert1]

If 9.5 digits are realistic noise-wise and the voltmeter can be 0.01 ppm stable for a year, that would be a large improvement over the HP 3458A - a factor 100 or so. I'd guess linearity could then be handled numerically. The meter should include circuitry for linearity check and calibration (type of autocal).
As doctorandus wrote in another thread, the oven is a MCU plus some sensors and maybe 10 discretes. If you want a nice solution, add a W5500 web server. These things have become very easy nowadays and dirt cheap.

Regards, Dieter

[coromonadalix]

But in some labs, it was shown on the web ...    there was a 10 or 12 digit meter shown,  they where used in a lab to measure / generate mass by electricity etc ...

some kind of balance .. with equilibrium ...   they said it was more precise for mass reference than the called silicon sphere

sadly  can't recall the right name  i'm french ...

was something like this : https://radwag.blog/en/why-is-the-new-kilogram-better-on-the-revolution-in-the-international-si-system-of-units-and-the-redefinition-of-the-mass-standard--2021-08-24

[moerm]

I'm really excited about what one can learn here. For instance that 'x.y digits' has not to do with log(counts) but with digits! That's super-mega-cool because 7 segment LEDs (plus drivers) are dirt-cheap, cheaper by order of magnitude than the "famous standard HP3458".
Exciting proposition: Just glue 3 4.5 digit cheapo-meters to each other and have a 12 digits DMM (modest version), resp. a 13.5 digit one (marketing version)! Yay!
Or that a 1.2 mio counts meter actually is a 2.4 mio counts meter because it has the 1.2 mio counts twice, once positive and once negative Yeah, yeah, I know, you still get only 6 digits plus an imaginary 0.5 but let's not be picky. After all *no* '8.5 digits' DMM, not a single one I know of, actually has 300 mio (and a bit) counts and, in fact, the "famous standard HP3458" doesn't even have half of what real 8.5 digits would require.

And before anyone dares to talk about precision and accuracy, let me clearly state that those are not important. It's all about resolution, linearity, and ... wait a second and let me have a look at the HPilentsight marketing blabla ...

Now, yes, yes, I'll admit it, the word 'measuring' has (or once had?) a clear and concise meaning, and yes, that meaning was not "crudely guesstimate", but still, remember it's all about [insert HPilentsight marketing blurb like 'linearity']!

Whut? Precision and accuracy, pardon, of course I mean 'uncertainty', are 6.5 digits only (on a good day) at best? True, yes, but still: I call that heresy!

And now if you'll excuse me, someone needs to add some display digits to a 5.5 digit multimeter. After all, we'll need no less than a 10.5 digits DMM to verify that 9.5 digits DMM once it exists!