9½ Digit Multimeter, feasible? - Page 1
Forum section: electronics / general

author: laichh
author_rank: Regular Contributor
timestamp: August 28, 2024, 07:34:00 am
content: Saw this post on StackExchange.com, how would you answer?https://electronics.stackexchange.com/questions/450454/why-isnt-there-any-9-5-digit-multimeter-or-higherThe real puzzle could be:"How far away are we from the 9½ digit multimeter?"That's 10 nV resolution on 10 V range!

author: Kleinstein
author_rank: Super Contributor
timestamp: August 28, 2024, 08:09:33 am
content: For the noise it is a question one how long one averages / waits and how stable the zero is. With care the stability / LF noise may be kept low for a reasonable time, though this is not easy. One may can get the ADC close to the 100 nV per square root of Hz level. This would mean averaging/integration over some 100 seconds to get an RMS noise down to the 10 nV level.For my DIY solution, that is really low noise (e.g. slightly below 3458 for the ADC noise, but still a poor reference), I get an RMS noise just below 500 nV for 25 SPS for a +-25 V full scale. With a little averaging (e.g. 2 seconds) the 100 nV digit is OK, though the Allan variance hardly goes below 30 nV. An thus 250 milion counts or just a little more than what is normally called 8 1/2 digits - maybe 8 3/4 with a little stretch. Given enough time maybe a SNR corresponding to 9 digits.However for a good meter there is more than the noise, when looking at a short.Already the 8 digit meters are somewhat limited by the low frequency reference noise. E.g. a single LTZ1000 ref. hardly gets below the 50 nV level for the Allan deviation. The reference limitation at least is not that bad if one measures a relatively small voltage, like just a littler over 10% and thus just at the edge where the next lower range does not work. So the extra ADC resolution can still be of some use. Also some tests can use the same reference.Another limitation is linearity. It gets already tricky to get much better than some 0.1 ppm and especially to test that the linearity is really that good. This starts with the problem that there is just not enough time to test at every possible reading, so no 100% testing possible.For a high end lab and use as a differential voltmeter, a JJA can give more than 9 digit stable resolution. It just is expensive and a bit tricky to use with the protection. Such high resolution also only makes sense if the signal source is also that stable. At the high end it is not just the meter, but also the source noise and drift.

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 28, 2024, 09:04:41 am
content: Just use a binary display - then good ADCs give you 24 digits!Beside the technical reasons that Kleinstein has explained: If you need more than 8 digits of resolution, then you need to buy or build a whole customized measurement system. I suppose 8 1/2 digits are the upper limit that is reasonable in a multimeter - and even in these multimeters only some ranges can really make use of this resolution.If you look for frequency counters or for timers you easily get more than 10 digits of resolution. You can buy interferometers for distance measurements that go down to 100nm at 100m range - that equals 9 digits. It depends on the application - but I just don't know a standard application for a voltmeter that requires more than 8 digits.

author: macaba
author_rank: Regular Contributor
timestamp: August 28, 2024, 09:55:24 am
content: Actual digits: no, physics & reality pushes back.Marketing digits: yes, DMM vendors are known to place their products in an entire digit category above what they could truly be pragmatically considered to be.

author: m k
author_rank: Super Contributor
timestamp: August 28, 2024, 10:40:38 am
content: 25V over 50ohms is 500mA, 100nV less is 2nA difference.What kind of a practical happening creates 2nA?If HP 34401A is idling and human touches its bumper the voltage reading goes sky high.

author: EC8010
author_rank: Frequent Contributor
timestamp: August 28, 2024, 10:41:16 am
content: Quote from: macaba on August 28, 2024, 09:55:24 amYes. My Agilent 34410A claims to be a 6 1/2 digit meter, but 12 is the largest number it can display before changing range, strictly making it a 6.08 digit meter. And the last digit is generally dubious, making it a reliable 5 digit meter. But that doesn't sound so impressive.

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 28, 2024, 10:42:07 am
content: We discussed this subject on the recent Metrology Meeting 2024 in Stuttgart:The StD or the Allan Deviation is used in DCV metrology (as communicated by Mr. Luis Palafox from PTB) as the decisive parameter of stability.At first, you need a very quiet DCV source, e.g. a 10V JJ array, which would give about 2nv rms @ 10V, or 2*10-10noise, about 10 "digits".The HP3458A already displays 9 digits, if you read via GPIB with OFORMAT DREAL, or if you use Statistics Mean and Standard Deviation.The performance with usual LTZ, LTFLU based references then is about 100 .. 200nV rms noise, i.e. 0.02ppm or a bit less than 8 Digits.This is a convolution (quadratic sum) of the source noise and the noise of the DMM.I regularly achieve such noise figures, and 9 Digits, by taking 16 measurements of NPLC 100 with statistics on the DREAL data with Welfords Algorithm.Measuring an ADR1000 based reference often gives noise figures below 100nV, i.e. 0.01ppm or full 8 digits.Mostly the flicker or popcorn noise of the internal LTZ1000A reference kicks in.Therefore, a more silent reference like the ADR1000 inside the 3458A, and several less noisy OpAmps on the ADC board would improve its noise performance, but you would again need a much less noisy DUT for judgement.ChuckB, aka Chuck Beuning demonstrated on the MM2024 both:He presented his new analog ultra low noise DCV reference Z10, having an StD / Allan Deviation near the level of a JJ array, i.e. 4..5nV @ 10V.Chuck, in cooperation with xdevs, they developed a 4 fold ADR1000 reference for the 3458A, and replaced 3 OpAmps for the +/-12V and 5V reference of the ADC.Chuck presented the Allan Deviation of the altered 3458A, measuring his Z10 reference, or a zero input on the 10V range, like in xdevs former DMM noise comparison campaign.For the Z10, he achieved about 40nV rms, i.e. 0.004ppm, and for the short 15nv rms, i.e. 0.0015ppm.Therefore, the 3458A is capable of delivering near 9 digits stable results with these changes.Frank

author: EC8010
author_rank: Frequent Contributor
timestamp: August 28, 2024, 12:22:49 pm
content: Fascinating stuff. Were any of the Stuttgart presentations documented for subsequent download?

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 28, 2024, 01:02:46 pm
content: Quote from: EC8010 on August 28, 2024, 12:22:49 pmYes, the presentations were made accessible to all the participants.Frank

author: EC8010
author_rank: Frequent Contributor
timestamp: August 28, 2024, 02:53:02 pm
content: But not to those who weren't able to attend.

author: Sensorcat
author_rank: Regular Contributor
timestamp: August 28, 2024, 10:54:06 pm
content: Quote from: EC8010 on August 28, 2024, 10:41:16 amMy result is 6.38 digits for your meter, with log(N) the number of digits for N counts. You have: 0.000 000 to 1.199 999 and -0.000 001 to -1.199 999; so N=2,399,999.

author: 2N3055
author_rank: Super Contributor
timestamp: August 29, 2024, 05:42:13 am
content: Quote from: Sensorcat on August 28, 2024, 10:54:06 pm6 1/2 digit nomenclature has got nothing to do with logarithms. And it is not about full scale range but display digits number.In this particular case it is full 6 digits on the right (0-9) plus first left digit that has only two states (0 or 1).20% over 1,000 000 is reserve range.Some meters (like R&S®HMC8012) claim 5¾-digit display (with 480 000 counts).. 0-4 range for first digit would actually make it what I would call 5 1/2 digit and 34410A would be 6 1/10 digits, but hey..It is marketing crap.Therefore I highly prefer counts nomenclature ... 480 000 counts or 1 999 999 counts. ± is implied.

author: guenthert
author_rank: Frequent Contributor
timestamp: August 29, 2024, 06:18:12 am
content: Noise is an obvious challenge, another is linearity. E.g. the old Datron 1271/1281 use only run-of-the-mill components and a conceptually simple ADC, but they put quite some effort into improving linearity of its integrator. Even just verifying the linearity of a long-scale DMM is a major undertaking. I'm afraid, for enthusiasts and small companies, best one can do is compare to a HP 3458A.

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 29, 2024, 09:53:18 am
content: Quote from: guenthert on August 29, 2024, 06:18:12 am.. it's INL would be good for 2*10-8or 8 Digits only.The initial question about a 9 1/2 digit DMM is kind of incomplete, or unspecific.The discussion therefore went into the direction of 'resolution', instead of stability and uncertainty of DCV measurements.I have answered the aspect of stability, which would give a lower limit for relative comparisons (transfer) between different DCV references, ignoring the INL error (between e.g. 7.15V vs. 10V references).In practice, if I make transfer measurements between my 11..12 references, within 30..40 minutes, I'm able to achieve about 0.05 ... 0.1ppm transfer uncertainty, due to mid term drifts of the references, and room temperature changes of about 0.3°C during this period of time. This time-frame already goes beyond the 10min. transfer specification of the 3458A, the Datron 1281 and the Fluke 8508/58/88A transfer specification looks nicer.Although the StD of each individual measurement is always at 0.01 .. 0.02 ppm, that means a 5 times higher uncertainty of my transfer and repeatability measurements.Therefore, relative DCV measurements with analogue circuits are mostly limited by the Zener references themselves. Maybe others can give some hints, how differential measurements (e.g. 3-cornered-hat) on a 10V : 10V level might improve these transfer uncertainties.Using a JJ array would virtually improve INL and noise / stability in the transfer process, but the uncertainty of any Zener Reference, even the Z10, will still stay at the 0.1ppm level, I guess.That means, that an 8 digit DMM is currently optimum for the actual reference technology, and 9 1/2 digits make no practical sense at all.If somebody would invent a quantum reference @ room temperature, that would change the game.Frank

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 29, 2024, 12:52:08 pm
content: I have wondered why they haven't upgraded, to 9.5 or even more. But my experience with any thing high precision is you are never that far away from the last few digits being a random number generator and no real use to anyone.From a non technical pov what is the gain of extra digits. For hardware developers there isn't a massive desire for it, there are researchers out there but how much are the asking for more digits.I would say we are hitting a wall slightly as we are getting to the point where the purity of copper the connections, the humidity, temperature and even the presence of people have an effect on the results. Though I am not an expert.

author: iMo
author_rank: Super Contributor
timestamp: August 29, 2024, 01:29:29 pm
content: It does not matter whether 9 or 11 digits are of any practical use, we human species will always strive to go more faster, more deeper, more higher, more accurate.. It is encoded in our DNA..

author: Sensorcat
author_rank: Regular Contributor
timestamp: August 29, 2024, 08:23:07 pm
content: Quote from: 2N3055 on August 29, 2024, 05:42:13 amMay I ask what makes you so sure about that? Is there a standard that defines it? A law maybe? If yes, please post your source. If not, everybody can decide himself what it has to do with. And the logarithm makes sense, since each digit represents one order of magnitude in counts of the display: log(1000)=3, log(10,000)=4, ...Quote from: 2N3055 on August 29, 2024, 05:42:13 amThe first digit has three states: -1, 0, +1.What is reserve and what is range is completely arbitrary.

author: 2N3055
author_rank: Super Contributor
timestamp: August 29, 2024, 08:48:48 pm
content: Quote from: Sensorcat on August 29, 2024, 08:23:07 pmYou are creating science where there isn't any. My source are old datasheets and manuals and many discussions how that nomenclature was "invented" by marketing and has nothing to do with science or exact math.There are old HP magazines where in one of those there were details about how 34401A was designed, there is discussion about x and x digits and how range is 1 000 000 with 20% overrange to comfortably measure around 10V etc..Whatever I said, take it as such, information was shared with you in good faith.If you want to make a science project of it and search for peer review, referenced sources and such, you are welcome to waste your time. You'll get nowhere. But hey have fun...

author: miro123
author_rank: Frequent Contributor
timestamp: August 29, 2024, 09:43:23 pm
content: Can we keep to the main subject "9½ Digit Multimeter, feasible?" You are free to start new treadThanks.Back to the question - 9½ Digit Multimeter, feasible?. I have many question- do you need 9 1/2 digit linearity- do you need 9 1/2 short term stabilitty- what is the definition of short term stability - lowest in alan dev or strictly specified time - e.g. 24h or 6h- do you need 9 1/2 digit DMM or only cat 3 DC voltmeter or nanovoltmeter or single lets asy +-10V range- last but not least. what about the noise?As soon as you have simple A4 specs of what you want to achieve we can discus the requirement feasibility and details.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 29, 2024, 09:53:33 pm
content: if it was easily doable we would have seen some ....

author: coromonadalix
author_rank: Super Contributor
timestamp: August 29, 2024, 11:49:54 pm
content: @miro123 what are your intent(s) reacting like this ....and 2n3055 answers are valid ...

author: ivo
author_rank: Regular Contributor
timestamp: August 30, 2024, 12:04:27 pm
content: As soon as they package up a programmable Josephson Junction source in a portable black box, we might get one

author: dobsonr741
author_rank: Frequent Contributor
timestamp: August 30, 2024, 02:36:37 pm
content: QuoteTwice as far of what you think. You also need a stable voltage source under test to measure. For-profit businesses will not create an instrument just to measure a treasured voltage reference all day.

author: Rax
author_rank: Super Contributor
timestamp: August 30, 2024, 03:37:48 pm
content: Quote from: dobsonr741 on August 30, 2024, 02:36:37 pmWhich... 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."

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 31, 2024, 08:43:44 am
content: Feasible, Yes.The question is why would you want to?I don't think it's happened partly as there is little interest in it. With the SI units they have been working hard to fix problems such as the meter getting shorter and he kg getting lighter that the the money and effort has gone to that. Then when it comes to the next levels of research I personally believe they are looking at what industry is looking for as that is where the money for going to come from.Without some new tech (better precision and accuracy) in other areas the we are stagnating and until the next chapter is here we can only just wait for it to happen. Chicken and the Egg.

author: dietert1
author_rank: Super Contributor
timestamp: August 31, 2024, 11:27:06 am
content: 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

author: iMo
author_rank: Super Contributor
timestamp: August 31, 2024, 12:02:42 pm
content: 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.

author: dietert1
author_rank: Super Contributor
timestamp: August 31, 2024, 04:24:28 pm
content: Quote from: iMo on August 31, 2024, 12:02:42 pmI don't have to. In my opinion there has been enough new technology to try and do better.

author: nimish
author_rank: Regular Contributor
timestamp: September 01, 2024, 03:28:59 am
content: Quote from: Rax on August 30, 2024, 03:37:48 pmThe 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.

author: BrianHG
author_rank: Super Contributor
timestamp: September 01, 2024, 04:09:35 am
content: 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 01, 2024, 07:33:02 am
content: Quote from: Rax on August 30, 2024, 03:37:48 pmThe 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.

author: iMo
author_rank: Super Contributor
timestamp: September 01, 2024, 09:18:09 am
content: Almost everybody plays with JJ these days..

author: dietert1
author_rank: Super Contributor
timestamp: September 01, 2024, 09:32:26 am
content: 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

author: coromonadalix
author_rank: Super Contributor
timestamp: September 01, 2024, 10:29:04 am
content: 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 spheresadly 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

author: moerm
author_rank: Regular Contributor
timestamp: September 05, 2024, 06:24:51 am
content: 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 countstwice, 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 whatreal8.5 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?) aclear 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!

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 19, 2024, 11:57:34 am
content: Just some metrology porn:

author: RoGeorge
author_rank: Super Contributor
timestamp: September 19, 2024, 12:17:24 pm
content: The video description saisQuote

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 19, 2024, 12:29:27 pm
content: Quote from: RoGeorge on September 19, 2024, 12:17:24 pmDid you need to spoiler it for anyone else???Okay, I didn't get it as a joke. It seemed quite legit that you can take a good instrument, reduce the noise, do more averaging and then get a stable display value for some time.It definitely seemed more legit than the 6 digits on the FNIRSI-USB-Tester:

author: moerm
author_rank: Regular Contributor
timestamp: September 28, 2024, 09:02:54 am
content: Quote from: Phil1977 on September 19, 2024, 12:29:27 pmAbsolutely! Who needs physics when we have statistics and marketing?You see, the length of the potato peels I got when I peeled potatoes and measured the length of each with a crude ruler with 1 inch resolution turned out be 2.3134 inches, although, granted, not a single peel, when measured properly with 0.1 mm resolution) actually had that length.Similarly, averaging plenty enough ADCs magically gain digits.(Important note: no children were harmed during that test! In fact, the four year old daughter of my neighbour very much enjoyed painting lines on a wood stick that then served for the "measurements")

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 28, 2024, 11:50:42 am
content: Each analogue measurement is only averaging.But I get your point. Already 8 1/2 digits are much more than a healthy brain can imagine. And though it really works well to make an 8-bit ADC measure 12bit if you well define your analogue filters and do enough averaging, it just gets exponentially more complicated with every additional bit or digit.Funny and hard to understand thing is that sometimes you have to add noise to increase measurement accuracy. Maths is strange sometimes...

author: RoGeorge
author_rank: Super Contributor
timestamp: September 28, 2024, 02:45:51 pm
content: Not sometime, alwaysmustadd noise. Without noise, the averaging trick doesn't work at all. And the noise has to be bigger than 1LSB. And not any kind of noise, it has to be uniformly distributed, or else you'll get lying results. Everything else has to remain perfectly constant, which in practice is not constant.Even so, averaging does not increase accuracy, nor precision, only increases the resolution.Accuracy, Precision and Resolution are 3 different aspects, they are not interchangeable words, and an instrument has to have all three to produce useful results. Infinite resolution would be meaningless without corresponding accuracy and precision.Now, since we are in the salad words realm, here's a reflection about metrology and the philosophical "Do we have free will?" (in the sense that the Universe is deterministic or not):The short answer is yes, we do have free will because "metrology".How's so? Well, there are known math examples of chaotic functions, where the same function will have a wildly different outcome when even the slightest numerical deviation is plugged into the function as the initial conditions. The fancy term is "Butterfly effect".Now, if we switch from math to the real world, to get the initial condition it means to measure the current state. And in metrology, a certain amount of error is inevitable. Therefore, even if we were to know all the physics, we still can not measure the current state with zero error, so the Butterfly effect will still cram into our prediction, so we will still have an unpredictable result.Even if the Universe were to be deterministic, our lives will still remain unpredictable because of metrological errors while measuring the initial conditions.Fate or not, you will appear to have free will anyway. Because "metrology".

author: Kleinstein
author_rank: Super Contributor
timestamp: September 28, 2024, 06:24:08 pm
content: The noise can be intrinsic to the ADC or amplifier and one may not have to add it. This is especially the case if one aims for very high resolution.One may not even need averaging because of quantization noise. A high numerical resolution and thus low quantization noise can be relatively easy with an integrating ADC. So numerical resolution well better than the other noise sources can make sense, as this can be one of the lower hanging fruits.Even with some chopping / AZ switching there are usually low frequency fluctuations / 1/f noise. These limit how much averaging makes sense, as longer averaging also extends the frequency range to lower frequencies. So there is usually an optimum time for averaging or diminishing returns for even longer averaging. In the Allan variance curve this shows as a minimum or at least no longer falling curve.Instead of long averaging for a single reading one may have to average over the whole experiment / reading sequence. With some experiments this can suppress the LF noise.

author: dietert1
author_rank: Super Contributor
timestamp: September 28, 2024, 08:45:31 pm
content: In general, when looking at averaged results we also have the ensemble with all the samples. We can check the statistical quality of those data looking at distributions and correlations.As far as i remember with data analysis there can be systematic uncertainties. They need to be assessed by modeling and simulation. In the end the rules are pretty simple - at least when enough samples are available. With very large ensembles ("cheap data") systematic errors will dominate.Regards, Dieter

author: moerm
author_rank: Regular Contributor
timestamp: September 29, 2024, 06:40:40 pm
content: Prolog: Feel absolutely free to find me boring and old-school!Quote from: Phil1977 on September 28, 2024, 11:50:42 am(As philosopy has entered the thread ...) Nope.(a) A measurement is gathering/determining quantitative information at some point in time. No more, no less. (b1) Everything that we humans can (really) measure is necessarily analog because the world directly accessible to us is, (b2) if you allow a quick reminder, "digital" is just a simplifying "bundling" of analog; instead of dealing with an infinite set of numbers we simply say e.g. "everything below 0.8 V is zero anything above 2.3V is 1 and everything in between is undefined".Quote from: Phil1977 on September 28, 2024, 11:50:42 amUhm, quite frequently deal with numbers far beyond 8 (or even 80) digits in my job.More importantly though, NO no amount of analog filtering 8 (or whatever) bits somehow gets you 12 (or whatever) bits. While, yes, that works in theoretical ponderings and is often used in science, measurements in electronics are, by their very nature, about physics. What filteringcando though is to get you more valid/"clean" bits in those your ADC got you. But if your ADC is 8 bits then you can't somehow magically get 12.Quote from: RoGeorge on September 28, 2024, 02:45:51 pmNope, the noise must berandombut I guess that's what you meant with "uniformly".But no, at least in most cases on shouldnotadd noise because that's counter-productive. The goal of filtering out noise is to get a "cleaner" result and pretty much always there's already noise in the chain. Besides what does one get by adding (random) noise and then filters it out? In the best of cases one gets what one had before adding noise.Quote from: RoGeorge on September 28, 2024, 02:45:51 pmYes and no. Yes they are different aspects and in particular, YES (hurray!) infinite, or let's say, much more resolution than accuracy and precision, is meaningless! (I'm very pleased to see that statement here).But how much is "too much" or basically useless? My personal view is that I'm not interested in more then n+1 digits resolution when accuracy and precision is n digits.Example: I don't care a flying fuck about an 8.5 digits multimeter with de facto 5.5 to, on a lucky day, 6 digits accuracy and precision (and that's thegoodones.But alas, companies are about profit which leads to marketing coming up with ever new BS. The sad state is that if one wantsreal6 digits measurements one is bound to buy an "8.5 digits" DMM.Quote from: RoGeorge on September 28, 2024, 02:45:51 pmCareful there! Philosophical excursions tend to look attractive but actually have plenty of spikes ...So, just two quick remarks:No, the fancy term is "avalanche effect". "butterfly effect" is the (frankly, idiotic IMO) hollywood term. And btw. functions with an avalanche effect are not (necessarily) "chaotic". In fact we usually try hard to have them be well deterministic - yet avalanche (e.g. in cryptography).And the main reason for us not being capable to make zero error measurements is not really complex but the simple fact that there is pretty much always (at least) one element in between us, who measure and the target of the measurement and/those element(s) usually introduce errors (e.g. DMM. Another factor often encountered is accuracy and precision (e.g. parallax error).Generally speaking statistics isnota friend of metrology. It tends to be useful though when dealing with large (measurement) result sets. And statistics *never* creates reality with one single (occasional) exceptions: humans.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 29, 2024, 08:01:26 pm
content: Statistics is also the area of mathematics that handles getting information out of uncertain / properbalistic data. For metrology it helps to know the statistics - ideally beyond the common normal distribution and uncorrelated noise case. It can provide quite some powerfull tools. Compared to quite some other parts of math it is also a relatively new area.Averaging or digital filtering in general works well, if there is sufficient noise in the data to avoid sticky bits from the quatization. If there is not enough noise already, it can indeed help to add some analog "noise", to make the quantization effect more random. Ideally one would start with enough numerical resolution, so that one does not have to add noise, but if the resolution is limited one may need to add noise to get a better result after averaging / filtering. The added "noise" can be more than white noise and even contain a deterministic part. The wanted effect of the added noise is to make the quatization error (and to some degree the DNL error) more random, so that it also be filtered to a large part. It may be counter intuitive, but it works. As an extrem many SD converters start with 1 bit and do filtering for something like 16 Bit and even more.For a DVM there are different limiting effects that set the useful resolution this are mainly: the numerical resolution / quantization limit, the noise, the stability (especially gain/ reference drift) and the linearity. With averaging / numerical scaling the numerical resolution is normally not the limiting point for the final result - this is more a thing for much lower resolution (e.g. 3.5 digits) meters. The quatization is more like one of many noise sources and at the high end usually one that is easy to take care of. With long scale meters the claimed resolution is usually the noise limit (e.g. RMS noise for 1 LSB step) - the quantization is often better and the stability and noise essentially always worse.With a slow high resolution instrument the noise and stability limit how good the linearity can be tested. With a very fast ADC the classic histogram methods can get around this limitation by averaging enough. So one effectively gets extra resolution, at least for the noise and quantization part. A high resolution DMM often already uses some internal averaging near to it's limits and additional gain from extra averaging is very limited. There are also just too many points to test and to low a data rate for much extra averaging (often not enough time for a complete test). So it is natural that one has larger uncertainties from INL and drift than from noise. It kind of has to be this way. One can't measure and let alone fix an INL error hidden in the noise.To get 6 digit accuracy one indeed needs to by more like a 8 digit meter - even there the stabilty is hardly that good for even a moderate time.

author: Echo88
author_rank: Frequent Contributor
timestamp: September 29, 2024, 09:51:27 pm
content: What are your propositions to improve on existing so called 8.5 digit DMMs like HPAK3458A/F8508A in regards to schematics/construction moerm?

author: dietert1
author_rank: Super Contributor
timestamp: September 29, 2024, 10:23:23 pm
content: An extra digit for an integrating voltmeter is cheap data. And systematic errors tend to be small when comparing measurements taken within a short time span. So for certain experiments (like a linearity check) that can be finished within some hours, the criterion cannot be the one year stability (or the lack of). You want some reserve digits in order to have digitization noise below analog noise level. Then you can average and make the statistical uncertainty small in comparison to systematic errors. One of the systematic limits of precision voltage measurement is thermal EMF. I think banana plugs and binding posts won't work for measurements at 9 digits below 10 V = 10 nV level.Regards, Dieter

author: moerm
author_rank: Regular Contributor
timestamp: September 30, 2024, 03:15:29 am
content: Kleinstein I largely agree with you plus I respect you too much to engage in a debate over details I see differently.So I restrain myself to one point only: NO, no amount of statistics creates or changes physical reality - and that's what measuring is about. It does however, as I indicated, sometimes create a (pseudo) reality in peoples minds.As I said, random noise in the digits one *really* has/gets can be (to a large degree) filtered out, e.g. by averaging. If in repeated, carefully executed, and properly verified experiments someone with a good knowledge level (like you) manages to get more precision and/or accuracy out of an ADC I'll accept that.But generally speaking statistics is useful (mainly if not only) in "post-processing" large amounts of (e.g. measurement) data.What you wrote about isn't what triggers me. What triggers me is (a) the fairy tale that one somehow can get more digits out of an ADC than it has, and (b) the bloody BS and the great lengths companies go in order to sell, often overpriced at that.(maybe also see the next part of this comment)Quote from: Echo88 on September 29, 2024, 09:51:27 pmNone. My approach is entirely different: how about designing, building and selling 6.5 digit multimeters as such, as 6.5 digit multimeters instead of adding some basically worthless digits and calling - and brazenly selling it as - an "8.5 digit multimeter" - aka acting honesty, which granted sadly has become a rarity nowadays, especially in anything related to money.Why would I not even try to design and build an 8.5 digit multimeter? Because I see and accept boundaries and it seems to me that nature has put a boundary at about 1 ppm. Yes, we *sometimes* can cross that boundary and I'm not saying that one shouldn't try although I myself certainly won't.Also note that we currently do *not have* 8.5 digit multimeters. We only have multimeters with about 6 *valid* digits with a label that says "8.5 digits" and a matching price.I get it, "more! better!" seems to be hardwired in humans and I lusted for a F8508 too but found back to rationality and realized that I just lusted for it but don't really need it. My contempt for basically cheating companies and marketing liars was helpful in that.So, I certainly understand people who strive to get a "top class DMM".

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 30, 2024, 05:51:09 am
content: Quote from: moerm on September 29, 2024, 06:40:40 pmBut to talk in examples that can be followed by a larger part of the readers: If you have a 1MHz 8-bit ADC available and need a 100Hz 12-bit then you don't need to go shopping. Normal distributed noise is reduced by sqrt(n) if n is the number of averaged measurements. That means if the ADC delivers 6 effective bits then you gain sqrt(10 000)=100 approx= 2^6.5 so your averaged result should theoretically have 12.5 effective bits. If your target are 12 data bits of which 10 should be effective then this method can work without any problem.Of course I agree you can't have any magic algorithm that creates a usable 12-bit signal out of a 8-bit ADC without drastically reducing its sample rate. "Garbage in garbage out" stays always valid.

author: dietert1
author_rank: Super Contributor
timestamp: September 30, 2024, 06:18:03 am
content: Contributor moerm is trolling this thread.There is nothing like a 1 ppm physical limit. Zener references with a stability of 0.02 ppm over several months have been demonstrated before. One can find the reports in this forum. And integrating ADCs stable to that level are commercially available.The 1 ppm limit is something created by the calibration lab market. If Fluke or Keysight labs with quantum standards don't certify to better than 1 ppm it's their choice. Quantum voltage standards are known to be good for about 0.0001 ppm, ten times better than necessary for a 9½ digit meter.Regards, Dieter

author: Kleinstein
author_rank: Super Contributor
timestamp: September 30, 2024, 09:53:17 am
content: Quote from: Echo88 on September 29, 2024, 09:51:27 pmThe HP3458 is kind of the benchmark meter, but it is still not made for just good INL and low noise. It still has some compromises to also get high speed.Today one can split the jobs for low speed at highest resolution very low INL and high speed at still good resolution over 2 ADCs, a bit like done in the Fluke8858 or DMM6500. There are now good SAR type ADCs that are an easy and good solution for the 1 kSPS-1MSPS range.The 3458 still uses a relatively low 12 V reference - a higher voltage there and equal reistors at the integrator input would improve on noise and make matching with the switches easier. Not a big deal, but an easy 10%. Another point is the rather fast modulation to get good high speed performance. Slower modulation could improve on the noise and to some degree also the INL, though there is the point dielectric absorbtion. To still allow for slower modulation there should be the option to used a kind of 2nd order integration for the FB (at bit like MS4 and NI meters) or as a larger step a more contineous PWM like FB as in the F8508 / Prema / Solartron meters. Another missed oportunity in the 3458 is filtering the reference: the ADC also react the higher frequency (e.g. 100 kHz range) noise from the reference, that is relatively easy to filter.An odd point in the F8508 is that for the 20 V range the signal is divided by 2 before the ADC. In my DMM I have used a different way to get a 20 V range. The input signal is split in a U/2 and -U/2 part. The auto zero cycle now measures these 2 parts instead of what HP does with 0 and the input signal, kind of loosing on the range by fixing one side to zero instead of also allowing for a vairable input signal and thus loosing half the theoretical possible input range. As positive side effect the input is essentially sampled all the time and thus less noise bandwith for the input amplifier and also for the signal source. By combining a positive and negative reading the even order contributions to the INL are canceled out.There is a principle limation from the resistors at the ADC input - for more than about a factor of 2 improvement in the noise one has to go low resistance and use really good, well matched resistors to fight thermal effects from self heating.To improve on the INL there is the option to do some dithering, e.g. with an added offset or using moderately different versions of the MS conversions. This can reduce the effect of possible local linearity errors, similar to idele tones.For the short time stabilty there would be the option to have thermal stabilization - nothing new, but it adds costs and power consumption. With modern parts the power consumption may not be that bad to start with - modern µCs and FPGAs consume quite a bit less than some 35 years ago when the 3458 was designed. Even OP-amps can be less power hungy (e.g. the OPA205 takes something like 1/10 the power of an OP07/LT1001 and is still lower noise higher BW).It may not be enough to get a full factor of 10 of improvement, but still quiet some possibilities.

author: NNNI
author_rank: Regular Contributor
timestamp: September 30, 2024, 10:17:32 am
content: Sorry to butt in to the conversation, but Kleinstein, could you elaborate upon the second order feedback in Multislope IV? I would also appreciate it if you could point me to resources regarding the same.Also interesting would be a somewhat more detailed explanation about the U/2 and -U/2 method, maybe you have already posted about it in one of the multislope threads?Thanks,NNNI

author: coromonadalix
author_rank: Super Contributor
timestamp: September 30, 2024, 11:07:56 am
content: was there some compare between the old 3458 and the new 3458 "AKA Black model" ??an 9 .5 digit dmm if it could exist, would not be useful for many DIY techs and some in the TEA, it would be surely used in a very stable environment or long term checks / drifts / references voltages etc ....not as an all day long dmm ?? at already at 7.5, 8.5 digits, you should be satisfied ? no ?and calibrating such ... what would be the $$ since we know a 3458 is in the 1 to 1.2k$ range ...

author: Kleinstein
author_rank: Super Contributor
timestamp: September 30, 2024, 11:33:38 am
content: The simple feedback in the multi-slope ADC is directly from the integrator and thus a bit like a 1st order SD ADC. 1st order SD ADCs are known to have strong idle tones, that is relatively static patterns in the feedback, that can cause local INL errors e.g. from dielectric absorbtion. 2nd oder SD ADCs show less severe idel tones. So the idea is to have a 2nd integrator (or an 1+ integrator) that is than used for the feedback during the run-up. This way the average voltage gets close to zero and the simple patterns near simple H/L ratios are more mixed up. The idea is not new and used in the patent US6970118 (NI meters). The run-down part would still be from the 1st order integrator part. The HP MS4 is some-what similar to the NI-meters, but looking at the patent it does not look like it uses 2nd order integration in the FB. Anway they use super fast modulation and a more PWM like FB and thus no issues with DA for this reason.I use the U/2 and -U/2 way in my DMM and it is described in the MS-thread. The idea is that the low side of the signal is no longer at the ADC ground but also moving, e.g. to minus the positive side to create a differential signal with little common mode voltage. By moving the low side, there is no actual gain or attenuator in the signal path. The inverter to move the low side only effects the CM voltage and thus no offset, gain or linearity error from there. The AZ cycle than alternates between the 2 sides instead of zero and signal and this way read the differential signal with the larger range.For the 4 wire resistance mode it is common practive to use the switching between 2 signals for a differential reading (sense Lo to sense Hi). The +- U/2 scheme is moveing "sense Lo" to maximize the usable range.The new black KS3458 is still very close to the original - mainly replacing old obsolete parts (e.g. the comparators and gate array) with newer ones. Still essentially the same specs and performance.

author: moerm
author_rank: Regular Contributor
timestamp: September 30, 2024, 08:53:32 pm
content: Quote from: Phil1977 on September 30, 2024, 05:51:09 amI know but frankly I consider that a fairy tale too. Because NO, you can *not* get 12 bits out of an 8-bit ADC, period.But you can get something like 12 bits out of asystem/instrumentif the sample rate is sufficiently high. What you actually get though, and that should be understood, is 8 (well, actually more like 6) *actually measured* bits out of the ADC plus another 4 (actually more like 6) bits out of statistics i.e. basically out of thin air).But then, that statistical "information" is not completely useless because it's at least based on what statistics need: a *large dataset*. With that one at least has some basis for "funny" statistics games.But an oscilloscope with (nowadays) billions of samples per second is one situation. With a DMM it's a very different situation because you donothave a sufficiently large data set.And *that*, DMMs were the topic here.

author: moerm
author_rank: Regular Contributor
timestamp: September 30, 2024, 09:17:27 pm
content: Quote from: dietert1 on September 30, 2024, 06:18:03 amFirst, why an ad hominem ("troll")?"no 1 ppm limit, zener refs ... 0.02 ppm ..."(a) Context! My statement was in the context of DMM.(b) I was talking about accuracy and precision,notabout stability."The 1 ppm limit is something created by the calibration lab market. If Fluke or Keysight labs with quantum standards don't certify to better than 1 ppm it's their choice."Yeah, because those corporation suddenly decide tonotturn something that would be very, very attractive for many customers into money! Well noted, after selling "8.5 digits" DMM, which actually are 6 digits DMM in terms of accuracy and precision - and that what measuring is about - for decades. Totally credible. Do you happen to have evidence that shows those corporations having crossed the 1 ppm barrier with DMMs?I call BS!The reality is that even the best standards the have are basically about 1 ppm standards, but 4 of them and only based on a bit of averaging those 4 they achieve a bit better than 1 ppm."Quantum voltage standards are known to be good for about 0.0001 ppm, ten times better than necessary for a 9½ digit meter."Cool, really, I'd be enchanted if only there wasn't a "small" problem: "Known to be good for ..." very, very highly likely means "calculated" but *not measured*! And I understand that because *with what* should they measure that?Feel free to tell me more about "Quantum voltage standards" once you can provide true, consistent, and repeatable measurements. Until then I take "quantum"- as what I think it is, a mix of fairy tale with a garment of some math.Don't get me wrong, I'd be very, very pleased if one day we had (even just) 0.1 ppm DMMs and/or standards, preferably over 90 days - but until then I'll verify and check wild claims.

author: moerm
author_rank: Regular Contributor
timestamp: September 30, 2024, 09:43:26 pm
content: @KleinsteinBravo! That's why I respect you, although IMO you are moving in a territory that is cumbersome, tricky and has a somewhat low reward-for-efforts ratio.Not only do you obviously have lots and lots of relevant knowledge but also are one of the few who actually work and "fight" for small improvements. Andthat, besides some potential (but unlikely) breakthrough in physics and/or electronics seems to be (and is in my mind) theonlyway towards more accuracy and precision.One hint though (again, I studied physics), albeit a bit loosely worded: heat means entropy and should hence be considered an enemy (here, in this context). Yes, I know the most stable references like LTZ1000 are heated, but actually IMO that is a tradeoff for a specific situation, namely the expected (in normal usage) rather wide (+-5°C) ambient temperature frame in which they are used. Or put differently there is a good reason for JJAs are being held close to absolute zero degrees: low entropy.If "yeah, yeah only about +-1ppm but over a (relatively) large temperature range and hence real world practical" is the situation, then heating, in order to at least achieve a *stable* temperature is a "good deal" - but when hunting to get an "8.5 digits" DMM a few tenths of a ppm better, heating is not a good companion.I wish you good progress in your work

author: dietert1
author_rank: Super Contributor
timestamp: September 30, 2024, 10:27:35 pm
content: National metrology institutes compare their JJA standards more or less regularly and know them to agree within about 0.0001 ppm. Anybody interested in voltage metrology has seen those reports, i mean they are easy to find if somebody is interested.That's what we call trolling: Members not interested at all in a subject writing long essays full of confusion. That 1 ppm limit proposal is telling it all.

author: moerm
author_rank: Regular Contributor
timestamp: September 30, 2024, 11:08:09 pm
content: Quote from: dietert1 on September 30, 2024, 10:27:35 pmThat may well be but *how* do they measure that? I don't care about "agreeing", that's just words, I want to see *facts* and data based on *measurements*.So?

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 01, 2024, 03:25:41 am
content: It seems moerm trusts authorities like metrology institutes but he seems to not trust statistics.But do you know who trusts in statistics? The whole science and consequently also the metrology institutes.It´s just very very short-sighted to disrespect statistics if you want any precision and accuracy.

author: dietert1
author_rank: Super Contributor
timestamp: October 01, 2024, 07:22:09 am
content: For example:https://en.wikipedia.org/wiki/Voltand its references.JJA standards work so well that the method has been adopted as the metrological definition of Volt in 2019. Since then the Volt can be derived from a known frequency using a JJA setup. It delivers voltages up to about 10 V. A precision comparison of two 10 V standards requires a nanovoltmeter for a direct comparison. Accuracy of the comparison can be about 1 or 0.1 nV.https://en.wikipedia.org/wiki/HertzFrequencies can nowadays be measured to about 15 digits and another quantum standard serves as metrological definition. As frequencies can be obtained to about 12 digits from GPS, this means anybody with the JJA setup can instantiate the Volt to about 10 digits. National metrology institutes can do better than GPS using their own frequency standards.Wikipedia has enough on statistics, too. I mean if somebody wants to learn.Regards, Dieter

author: Echo88
author_rank: Frequent Contributor
timestamp: October 01, 2024, 09:46:29 am
content: JJAs can be intercompared via nullmeters like a HPAK34420A:https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32759https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32308Abstract: The majority of Josephson Voltage Standard(JVS) intercomparisons have been performed by using Zener voltage transfer standards and a protocol based on the Measurement Assurance Program (MAP) with uncertainties in the range of a few parts in 10^8 at 10 V that are limited by the Zener characteristics.In order to improve the uncertainty of the comparison, protocols using a compact Josephson voltage standard (CJVS) as the transfer standard have beendeveloped. The uncertainty using the CJVS in the comparison can be in the range of a few parts in 10^9 at 10 V.The array-to-array direct comparison using the conventional JVS or programmable JVS (PJVS) can further improve the uncertainty of the comparison to a few parts in 10^10.

author: moerm
author_rank: Regular Contributor
timestamp: October 01, 2024, 11:25:06 pm
content: Quote from: Phil1977 on October 01, 2024, 03:25:41 amNo, I do trust metrology institutes to (quite) some degree but not fully. In fact you yourself laid out the reason: "The whole science and consequently also the metrology institutes" - which btw is largely true but not fully; there are some fields in science where statistics plays a rather minor role, if any.The main two reasons: while statistics can be useful it by its very nature always has some distance from reality. So, averaging on a scope can help to get a clearer (literally) image, on a multimeter it can get rid of (random) noise, but it's only meaningfull iff based on real measurement data. As soon as statistics (or more precisely statistical methods) go beyond actual physical data that may be useful only for interpretation.That said, metrology institutes and I (and all of us) have a common problem: we have to do with the best that's available, which in my case (and highly likely yours too) is national standards and in their case is not really sufficiently accurate and precise (and frankly IMO questionable) instruments. That's just how the world is.Second reason: science, or more precisely "science" that is, to provide two examples, idiots telling us that sex is determinded *sociologically* (or whatever BS) but definitely *not* biologically. And idiots telling us that the laws of physics are valid in the *whole universe*, which is obviously not a tenable statement, although quite likely true, because it's based on a ridiculously tiny empirical space (not even one complete solar system). Now, if some secondary teacher tells that nonsense he can be forgiven, but if a scientist tells it he obviously missed some basic and important lectures.In case you're interested look up "quantors". Math (and Math is my yardstick) tells us that if a proposition is not true for even a single element of a set it can't hold for the set.Btw. "The whole science and consequently also the metrology institutes" is an argumentum ad verecundiam and would not stand in (real) science. "The whole science" also told us for centuries that the earth is flat and the sun circles around it ...Quote from: dietert1 on October 01, 2024, 07:22:09 amThank you for the links which you seem to consider a reference.Unfortunately though you only provided links supporting your belief system but *ignored my question*, so I'll repeat it for your convenience: *how* do they measure that?(maybe also see my response to @echo88)

author: moerm
author_rank: Regular Contributor
timestamp: October 01, 2024, 11:26:11 pm
content: Quote from: Echo88 on October 01, 2024, 09:46:29 amFirst, thank you for responding to my question to @dietert1, I appreciate that.But while I very much welcome NIST's and other's striving for ever so slightly improving what they have I do not really trust it, sorry. For multiple reasons, a major one being the HPAK34420A being the weak link in more than one regard. For one it's as far as I know *not* used (nor I guess even usable) at cryo-temp (say below 70° K) as is a JJA/JVA and hence has way more noise, temp-drift, etc. Moreover it's datasheet talks about 2ppm basic 24hr (presumably +-1°C) accuracy (and only in 1 range albeit gladly in the one that seems to be used) which is orders of magnitude higher than the required level for ppb accuracy and precision. Also note that an additional range "uncertainty" of 1ppm (1000 ppb!) applies. And there's also DC noise and DC noise vs source resistance, the former being close to half a ppm in the 10V range. Furthermore the numbers provided seem to be for the 6.5 digits mode (vs the nominal 7.5 digits capability). Unfortunately the counts of the meter/ADC seem to not be mentioned so I presume it's 12 mio. which in itself indicates (common for (not only) them cheating) hint: even 20 mio would only be 7.3 digits, but may explain their talking of 6.5 digits measurements.One laudable point though: at least they don't simply use banana jacks (as most 7.5 and even 8.5 digits DMM regrettably do) but a shielded jack/connection.All in all what I see is this: They try hard, they really do, but I see no solid basis for assertions like "only a few ppbs ("uncertainty")" or even "fractions of 1 ppb". And I certainly see no solid basis (at all) for "10^-10" precision, let alone in the context of checking accordance between multiple standards, even less so, when hours of flight and oceans are between the "homes" of the two (or more) standards.Summary: I appreciate their work, and no doubt they *do* try hard, but (a) they have to work with what's available (e.g. questionable "super-meters") plus while the logic "let's use our capability to measure (and produce) frequency with high precision and accuracy to also create a very precise and accurate voltage" seems to make sense and highly likely works, one can only be really sure of what one can reliably measure.Example: certainly quite unlikely, but can one really say with certainty that the known mechanisms, laws, and techniques that work so well in the voltage ranges we *can* reliably measure, still hold true in significantly smaller ranges? Maybe some weird factor enters the game that is absent or insignificant/irrelevant in the ranges we can measure?Again, quite unlikely, but we can't be certain unless we can measure and verify (and *fully understand*).EpilogSo what? I for one am quite happy with a 1 ppm over 1year +-5°C reference and knowing that say, 10 times better would be available if needed.Also: Hey, I'm just me, just some guy and not of importance. Obviously I *can* learn and change my mind if someone convince me, and quite some people did in my life. I am grateful for the effort they made.You (not specifically you, but those involved in this discussion) did not convince me so far. But so what? Again, I'm just me and not important. Just let me think in my way as I'm totally ready to not force-feed to you what and how I think. But maybe you think a bit about what I said, just as I thought about what you said (and even glanced over what you linked (except wikipedia).

author: The Soulman
author_rank: Super Contributor
timestamp: October 01, 2024, 11:59:38 pm
content: Obviously the HPAK34420A or similar would be used as a null-meter:https://en.wikipedia.org/wiki/Null_detectorWhen I was a little kid (long time ago) someone thought me: "you can't talk and listen at the same time".Learning requires listening/reading and not much talking/writing.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 02, 2024, 07:44:35 am
content: He´s free to think and to some extent to write what he wants, but I stop reading if someone gets esoteric.And one of the biggest differences between esoterics and science is the usage of maths and statistics

author: Kleinstein
author_rank: Super Contributor
timestamp: October 02, 2024, 08:29:44 am
content: The reference accuracy for a null meter is not relevant. That part of the error is proportional to the reading and at the intendet zero reading also zero. So the HP34420 is OK as a nullmeter.For the really sensitive tests with the JJ references they sometimes also use superconducting null meters and this way avoid also the thermal EMF from going from low temperature to room temperature. These can be way more sensitive, down to the sub pV level to allow precise comparsisons even with single Josephson junctions. However they are by design null-meters with a low input impedance (e.g. µH range inductance, no resistance).@moerm: I totally agree that there is limited need for even higher resolution meters. The quoted resolution is for the noise limit and naturally the accuracy is quite a bit lower (e.g. 1 digit). Even just the transfer accuracy for a small range is not the same as the resolution. To allow testing a meter to certain level one needs noise levels that are something like a factor of 10 lower. The noise part is one of the easier parts to handle. There are even parts where one has to compromise between noise and accuracy (e.g. low resistors for less noise, but more INL from self heating).The question is more if a meter with accuracy of lets say better than 0.1 ppm for some time frame is feasible.

author: Echo88
author_rank: Frequent Contributor
timestamp: October 02, 2024, 12:23:04 pm
content: Did i read this correctly "a JJA seems to work"? Its the basis for SI-units Mr physics guy.Youre completely right Dieter, he is a troll.I wonder if user rhb has already done his aging drift elimination of zeners by statistics as claimed, he seems like an antithesis to moern who hates statistics. Anyway, time for hobbystuff and the quest for lower noise refs, instead of wasting it on trolls.

author: dietert1
author_rank: Super Contributor
timestamp: October 02, 2024, 02:14:37 pm
content: There's no forest in antarctica, so he's coming here. There may be other, hidden reasons as well.

author: mendip_discovery
author_rank: Super Contributor
timestamp: October 02, 2024, 06:56:31 pm
content: SoooooThe International types have been voltage measuring for a while.Zenner Voltages,https://www.bipm.org/kcdb/comparison?id=17691 V,https://www.bipm.org/documents/d/guest/bipm-em-k11_graph-1-v-may-202410 Vhttps://www.bipm.org/documents/d/guest/bipm-em-k11_graph-10-v-may-2024JJA,https://www.bipm.org/kcdb/comparison?id=17791 V,https://www.bipm.org/documents/20126/45253381/RESULTS+BIPM.EM-K10.a-Sept-2021+GRAPH.pdf/4c9b4b53-82b7-f517-e6f6-ea8913a01ccb10 V,https://www.bipm.org/documents/20126/45253381/RESULTS+BIPM.EM-K10.b-Sept-2021+GRAPH.pdf/64bdc9c1-872a-c484-3084-d35d30ea864fZener gets to uV/V but the JJA gets down to the nV/V range.https://www.bipm.org/documents/20126/45254323/APMP.EM.BIPM-K11.1.pdf/cdb6332a-c7b8-0334-eec6-0220d6256901Fluke 732B,Temperature,17°C to 27°C10 V output: -8.5 nV/V (°C)-1, standard uncertainty 4.7 nV/V (°C)-1.1.018 V output: -13.5 nV/V (°C)-1, standard uncertainty 6.1 nV/V (°C)-1.HumidityEach of the two voltage outputs was measured at 35%, 70% and again at 35% relative humidity. The temperature was set at 20°C and the duration of measurements at each humidity setting was between 6 and 8 days, with the voltage measured and recorded automatically every hour over this period. For these automatic measurements, a second Zener (owned by NMIA) was used as a reference at constant relative humidity.The results were:10 V output: +0.56 nV/V (1%)-1, standard uncertainty 0.07 nV/V (1%)-1, with a time-constant of approximately 1.5 days. Thus for a change in relative humidity of (for example) 45% to 46%, the voltage rises by 0.56 nV/V.1.018 V output: any response to humidity change was masked by the noise of this output, expressed by a relative standard deviation of about 87 nV/V. By contrast, the relative standard deviation of the 10 V output was about 38 nV/V. These two measures of noise include the noise of the NMIA reference Zener mentioned above.Pressure,The response of the Fluke to a change in pressure was immediate, with no observable settling time.10 V output: +1.6 nV/V (hPa)-1, standard uncertainty 0.2 nV/V (hPa)-1.1.018 V output: +1.7 nV/V (hPa)-1, standard uncertainty 0.2 nV/V (hPa)-1.From this, I can see we can measure deeper. I have yet to see a multimeter with correction abilities for ambient pressure and humidity. But if I was building a 9.5-digit meter I guess you would have to start taking that into account.81.96 hpa variance over the past year where I live so I have at least 131 nV/V of error already.

author: dietert1
author_rank: Super Contributor
timestamp: October 02, 2024, 07:22:54 pm
content: Above there has been some discussion about a complete voltmeter built inside a (near) hermetic enclosure. I want an IP66 kind of enclosure with a rubber gasket that is easy to work with. Those are available in many different sizes.Making it an oven for constant temperature is easy, using some PID controller with heaters or Peltier elements. For humidity i have seen good results, too, as we can buffer humidity with some silica gel inside the enclosure. We found seasonal variation of less than +/- 1 % and +/- 0.1 % should be possible.Recently i started to look at constant pressure solutions and it seems a bit more difficult. Research of leakage modes isn't complete yet. In the end we have those nice integrated digital sensors, like the BME680. So one might use their results for numerical compensation.Regards, Dieter

author: uer166
author_rank: Super Contributor
timestamp: October 02, 2024, 07:55:48 pm
content: Quote from: moerm on September 30, 2024, 08:53:32 pmAnd what about Sigma-Delta ADCs? Are those not 1-bit ADCs that average a reading however many times you need to get to 24+ bits?With gaussian noise or intentional noise shaping, you definitely CAN make a 12-bit ADC out of a 8-bit one, it ain't magic..

author: moerm
author_rank: Regular Contributor
timestamp: October 03, 2024, 12:07:35 am
content: Quote from: Kleinstein on October 02, 2024, 08:29:44 amAs usual a fine post showing deep knowledge and lots of experience that is, a post one actually can learn from or at least think about and ponder. Thank you!Probably even more importantly a post that doesn't boil down to "meh, you attack my belief system so I'll fight not only what you say but even you as a person!" like quite a few here seem to approach my posts.A man who can't calmly listen and react to a view he dislikes is both, someone with a weak belief and a weak man. You obviously are not such a man, and such, a man I'm taking seriously and whose arguments I ponder, think about, and search for knowledge that extends mine.Btw, I appreciate all the work they do at NIST and other similar institutions. I don't really trust the let's say far out edges (like "< 1 ppb") and think that they stand on somewhat floating grounds there, but I nevertheless appreciate their experiments, attempts, and work.My main concern is the widely spreading diluted understanding - and practice - of science which I increasingly often have to put into '"'.Example: the "holy" gravity constant is *not* constant, but hey, as long as the people herds eat the BS it's OK (it seems). And soon it's preached as "everybody knows" and "wikipedia" blabla. And of bloody course the corporations are more than happy to build on that and to sell BS like e.g. a "6.5 digits DMM" with actually less than 6.1 Digits (based on counts) and an "uncertainty" of not ~0.3, not 1 but >20 ppm in its best range (10V) that is, that DMM is in fact not even a 5.5 digits one but closer to a 4.5 digits one (Note: I calculated the average over 2 measurements, one measuring a value of 1/1000 (10 mV) and one of 95% of the range (9.5V) that is at the periphery of typical measurements).But some fervent believers accuse me of disliking math, being esoteric, unscientific, etc....

author: moerm
author_rank: Regular Contributor
timestamp: October 03, 2024, 12:11:53 am
content: Quote from: Phil1977 on October 02, 2024, 07:44:35 amUhm, I'm quite deep into math almost every (work) day and I'mnotagainst statistics generally but I'm against statistical "magic". In fact I even clearly said that math for me is the yard stick.So you dislike esoteric but magic is OK? - OK, noted.Quote from: Echo88 on October 02, 2024, 12:23:04 pmWell, I guess a few centuries ago I would have been burned as a heretic by the vatican ...Btw. SI units didn't exist then but they had "standards" too. Like e.g. the width of "an average men's thumb".Btw I can sell you the original Eiffel tower and if you buy two I'll even give you 30% rebate!Kindly do yourself and me a favour and stop making attempts to paint me as stupid in order to shut me up.Quote from: dietert1 on October 02, 2024, 02:14:37 pmOh no, how terrible, you got me red-handed! OK, I'll confess: I indeed have a hidden agenda. I'm sent by a fervent esoteric (secret, of course!) group to, once settled in, sell space travel tickets to a "nearby, possibly earth-like planet only seven hundred thousand light years away"!Quote from: uer166 on October 02, 2024, 07:55:48 pmAs I said, I'm not here to force feed my view, not even to convince anyone. So, if you feel that what you wrote really is true and correct I simply wish you fun and success building a 3.5 digits DMM around a 8-bit SD ADC (if you find one you like).

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 03, 2024, 05:54:12 am
content: It´s really time to stop this discussion because it´s that ridiculous that it must be trolling...Anyhow, though statistically seen its useless: Enhancing ADC-resolution by noise shaping and averaging or Sigma-Delta-ADCs is neither esoteric nor magic. It´s pure maths, and for someone with a scientific or engineering background it´s not even hard to understand why it works.It´s nothing like noise-reduction algorithms for images or music that are using psychological or AI models to interpret the signal. I could understand if you are against these methods in "pure metrology" - but resolution enhancement is absolutely inside the entropy laws.Statistics, entropy and especially the second law of thermodynamics are really hard to argue with. Empirical knowledge and experience of most smart people of the world give more than enough trust that they are valid.

author: dietert1
author_rank: Super Contributor
timestamp: October 03, 2024, 08:56:44 am
content: Sometimes i think this forum doesn't support scientific discussion. Whenever i tried, my contributions were buried under a pile of .. We can hardly mention the 3458A except for praising it and a thread like this one is doomed.Anyway let me mention that i got a nice result today regarding the making of a constant temperature, constant humidity and constant pressure oven.Regards, DieterEdit: A 2018 NIST report of a 0.1 nV comparison between two programmable Josephson voltage standards (11 digits).https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925369#:~:text=This%20paper%20presents%20results%20of%20the%20first%20fully%20automated%20direct

author: Echo88
author_rank: Frequent Contributor
timestamp: October 03, 2024, 08:30:23 pm
content: You beat me to it Dieter.Im not that quite there yet with my constant T/P/H chamber which i intent to use for the ultra low noise Vref project with supercaps and foil caps, hope to post some stability results in a few days now that i got those BME280 workingTemp regulation right now assures an attenuation factor compared to ambient temp variation of about 250 using an analog PI-regulator.Any opinion if a bipolar current source for resistor measurement would be beneficial in an imroved DMM compared to the regular current active/inactive for TEMF compensation like Fluke does with their "Tru Ohm" claim? I dont see the benefit.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 03, 2024, 09:28:58 pm
content: There is a small advantage in switching between a postive and negative current instead of current on / current off. It gives more signal with the same self heating or less heating with the same signal. It depends on the resistor range if this is relevant and if switching the current is used at all.Allowing postive and negative currents also gives some consistancy check as 2 separate values.

author: O.B.Don
author_rank: Newbie
timestamp: October 08, 2024, 12:43:47 am
content: Quote from: dietert1 on October 03, 2024, 08:56:44 am

author: laichh
author_rank: Regular Contributor
timestamp: October 08, 2024, 11:17:39 am
content: Hi O.B.Don,I am glad that my original question triggers such a chain effect.Take a look at the datasheet of LTC2500-32, on page 8, the chart for DC histogram with different number of averaging from DF = 4 to DF = 16384, it shows that the standard deviation of the histogram shrink with respect to sqrt(DF). That's the power of math & statistic, just Google "Central Limit Theorem" to learn more.

author: O.B.Don
author_rank: Newbie
timestamp: October 09, 2024, 01:02:52 am
content: The challenge with the LTC2500-32 ADC is that digital filtering will reduce the spread of the data at a single value input from slightly over ±7.5 ppm with no filtering to about ±0.1 ppm with DF=1684 for a SSINC filter.Averaging or digital filtering however may not necessarily reduce the overall INL of the device, so the device's INL spec may ultimately limit the the "accuracy" of the device.Improvement in the INL, by averaging, is dependent upon the type of ADC, (delta-sigma vs SAR for example) and how smooth and predictable the INL curve is or isn't. If the INL curve is sufficiently smooth and predictable it allows one to calibrate the ADC's range at a smaller number of points and then develop a calibration compensation equation that with sufficient noise and averaging may allow an effective INL that is better than the published specifications.If an ADC has a low INL by design, then averaging of the signal along with enough noise to span several LSB digits of the ADC can result in more effective calibrated bits.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 09, 2024, 07:48:00 am
content: The averaging is only effective like the square root of time if there is not extra 1/f or similar low frequency noise. The auto zero switching / chopping can avoid this for a large part of the ciruit, but there is still a part before the switches that is sensitive to thermal variations. Also the reference side has 1/f noise. So the idea of using more time is somewhat limited. For the really long times there are usually also effects that make things worse the longer it takes ( the Allan variation curve goes up again). So it really makes sense to start with low noise.Some of the very slow meters (Solartron 7081 , Fluke 8508, Datron1281) take 50 or 25 seconds for a single 8 digit reading. Much slower gets really inconvenient for the user too.Very long time averaging only works well if the signal source itself is modulated. I have used long time averaging with a lockin amplifier up to 1000 s averaging per point and it was still roghly on the 1/sqrt(time) slope. However it usually does not work that long for DC.

author: iMo
author_rank: Super Contributor
timestamp: October 09, 2024, 09:24:53 am
content: Quote from: O.B.Don on October 09, 2024, 01:02:52 amDid somebody try with the LTC2500-32 actually?? I'm still looking for an opensource ADC around this chip (having them for years in my junkbox among the others famous "32bitters")..