How many digits can a meter have? - Page 1
Forum section: electronics / testgear

author: AG6QR
author_rank: Frequent Contributor
timestamp: March 13, 2015, 08:31:33 pm
content: Handheld meters with three and a half digits are common. Four and a half digits isn't unheard of. Bench meters may add a bit more resolution. The Agilient 34461a boasts a full six and a half digits. Have you ever seen a meter with more than seven digits? Ten digits? Twenty digits? A hundred digits? Surely we're getting into the realm of impossibility here...Well here's a meter with a full sixty-thousand digit display! How do you scroll through such a thing?http://www.gossenmetrawattusa.com/products/measurement/multihandheld/MetrahitEnergy.htmlTalk about resolution!The METRAHIT ENERGY has a resolution of 60,000 digits and has more than 35 different measuring functionsAll important power factors can be precisely acquired with simultaneous current and voltage measurement with a resolution of 60,000 digits.I know, someone is going to claim it's a typo; they meant 60,000 counts, not 60,000 digits. But they clearly said 60,000 digits not once, but twice! The people who write those marketing blurbs, especially for a quality company like Gossen, must know the difference between counts and digits, no?And it's not just that web page where the claim is made:http://www.gossenmetrawattusa.com/products/measurement/PDF/MetraHitEnergy.pdfhttp://www.gossenmetrawattusa.com/products/measurement/PDF/MetrahitEnergyTechnicalData.pdfhttp://www.gossenmetrawattusa.com/products/measurement/PDF/MetraHitEnergyInstructions.pdf

author: wiss
author_rank: Frequent Contributor
timestamp: March 13, 2015, 08:58:09 pm
content: Solartron used the terminology "digits" where I would use "counts", at least in the manual for the 7075."Adjust R402 for a reading 0.000000 +- 20 digits"

author: gilbenl
author_rank: Regular Contributor
timestamp: March 13, 2015, 09:05:17 pm
content: 8 1/2 is the highest I'm aware of (Agilent 3458A, Datron/Wavetek 1081/1281, Prema 8017). The OP does raise a question that I've had-What is the limiting factor for DMM resolution? I assume its the reference given that the "best" are accurate to 1ppm or are there other factors at work?

author: max_torque
author_rank: Super Contributor
timestamp: March 13, 2015, 09:22:07 pm
content: It's perfectly possible to make a meter than can very precisely come up with a completely inaccurate reading!Ie. take a lot of samples, over a long time period, do some bulk averaging / oversampling, spit out a number with a massive number of decimal points. However, in the real world, the ACCURACY of that number would be awful, unless the meter was incredibly well constructed. The fact that meters pretty much stop at around 8(ish) digits suggest at this point the law of diminishing returns has well and truly kicked in ;-)

author: Matje
author_rank: Regular Contributor
timestamp: March 13, 2015, 11:00:50 pm
content: Quote from: AG6QR on March 13, 2015, 08:31:33 pmThe people writing these marketing literature are sales droids AKA sales weasels (scum, in other words), nowadays likely some innocent clueless unpaid intern.They probably can't find their asses, with a map.Anyway, 60K digits is physically impossible, ask the nearest physicist for the reasons. Heck, there seems not even to be a unit prefix for 10**-60, seems to stop at 10**-24.

author: Vgkid
author_rank: Super Contributor
timestamp: March 13, 2015, 11:18:32 pm
content: Could be a translation issue, referring to a 60,000 count meter, though that is a strange number.

author: dacman
author_rank: Frequent Contributor
timestamp: March 13, 2015, 11:33:48 pm
content: I agree. The manual says digits when it means counts, and it has ranges of 60mV, 600mV, 6V, 60V, and 600V, with resolutions that make it a 60,000 count meter.A Fluke 8508A is another with 8.5 digits.If the repeatability is > 10 counts, then it's in the noise region and more digits would not be useful (IMO). The 3458A shows up to 8.5 digits on the front panel display, but returns a double precision 15 digit number over the IEEE bus.

author: DanielS
author_rank: Frequent Contributor
timestamp: March 13, 2015, 11:37:16 pm
content: Quote from: gilbenl on March 13, 2015, 09:05:17 pmI think practically everything in the analog signal path becomes a potential limiting factor at that point. The voltage reference is just the fundamental building block which can single-handedly make or break accuracy across all measurement ranges.Once the whole analog chain is operating at the same general accuracy level from input and reference to ADC, you have to improve everything by an order of magnitude to gain an extra digit of absolute accuracy.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 13, 2015, 11:44:18 pm
content: http://www.keysight.com/en/pd-1000001297:epsg:pro-pn-3458A/digital-multimeter-8-digit?&cc=CZ&lc=engIt is funny that the3458Awas developed in 2000 (or earlier) and it is still sold. There is no better & newer multimeter yet.

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 14, 2015, 12:13:52 am
content: I guess the more appropriate question might be ... To how many digits is the ultimate reference that the hypothetical meter would have to calibrated against, to prove that it's display has meaning ?How many digits does NIST have the ability to guarantee as a reference ?

author: ConKbot
author_rank: Super Contributor
timestamp: March 14, 2015, 12:15:06 am
content: Well for one, where do you get a calibration standard! A meter that can measure 10 digits isnt any good if you cant prove its correct. NIST's references are only down to 0.04 PPM, and the 3458A boasts a 0.05 ppm dcV transfer accuracy.http://www.nist.gov/calibrations/voltage.cfmand if I'm reading that right they only promise 1 ppm uncertainty at the lowest on their DC cals?

author: dacman
author_rank: Frequent Contributor
timestamp: March 14, 2015, 01:02:07 am
content: Here is a link to the Fluke NVLAP certification. It indicates that Fluke can do a 0.06 PPM 10 Vdc cal on site and that their Josephson Junction (JJ) is 0.01 PPM at 10 Vdc (calculated from 5 nV/V + 50 nV at 10V).Page 16 of the document below has the certs.http://ts.nist.gov/standards/scopes/1050160.pdf

author: Rick Law
author_rank: Super Contributor
timestamp: March 14, 2015, 02:29:33 am
content: Quote from: max_torque on March 13, 2015, 09:22:07 pmWell, your digits can't go infinitely long. At some point, quantum effect starts to dominate and "current" or "volt" would be meaningless. Ohm's law is not going to hold, nor would most other "laws" down at that level.On the other hand, if you do get a 40 digit DMM with +-10 digit accuracy at +-1%, you can prove Heisenberg to be a fool.

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 14, 2015, 03:35:21 am
content: Quote from: Rick Law on March 14, 2015, 02:29:33 amYes. After reading NBS (now NIST) papers tonight about the U.S. Legal Volt, and how careful they are not to do anything that might adversely affect the primary cell group. Amazing stuff.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 14, 2015, 07:30:10 am
content: You can take 20, 30 digits, however many you want... but you'll never eliminate systematic errors to that level (how could you calibrate it?), and you'll be waiting somewhere between days and "age of the universe" to perform the measurement (because by the Nyquist-Shannon theorem, the bandwidth and therefore noise floor must necessarily be extremely low -- averaged over a very long period).Tim

author: Smith
author_rank: Frequent Contributor
timestamp: March 14, 2015, 08:19:01 am
content: A good reference, extreme low noise psu, complex analog frontend and verry high resolution (and high linearity) adc would only be the first of worries. What about cost? Just compare a 6,5 7,5 and 8,5 digit meter. I do think 8,5 digit is more than enough. I am not even sure if we will see any 9,5 digit meter in the near future, due to the parts needed for such a device. Cabling would get problematic too.Read keithleys low level measurements handbook, ithas lots of info.But all together, how many (if any) would need 9 digits or more. And i do mean who needs, not who wants

author: Ericho
author_rank: Regular Contributor
timestamp: March 14, 2015, 09:06:29 am
content: Never needed anything more than 50.000 counts.A 6,5 digit meter would be fun to have and play with, but the same kind of money can buy more usefull thing for me.Resolution of 1uV is something i use and need a lot, my handheld dmm's do that OKI can't imagine how a 8 1/5 or more digit bench DMM can be usefull for the average home lab. unless DMM themselfs are a hobby

author: HighVoltage
author_rank: Super Contributor
timestamp: March 14, 2015, 09:22:48 am
content: On the Gossen Metrawatt website you find the following:English Version:Thanks to simultaneous TRMS current and voltage measurement (AC, AC+DC and DC) with a resolution of 60,000 digits, all important power quantities can be precisely acquired.German Version: (Deutsch, top left button)Durch die gleichzeitige TRMS Strom- und Spannungsmessung (AC, AC+DC und DC) mit einer Auflösung von 60.000 Digits können alle wichtigen Leistungsmessgrößen präzise ermittelt werden.We call this modern mixture out of German and English: "Denglish" in Germany and we see it everywhere these days.Because of this, sometimes Germans use English words in the German language with different meanings, as in the original English language.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 14, 2015, 09:30:26 am
content: Quote from: AG6QR on March 13, 2015, 08:31:33 pmVery simple..The number of digits of a measurement instrument is practically limited to theuncertaintyandstabilityof the physical value or unit, which you'd like to measure!Adding more digits to the display would be useless, as these would jitter only.Uncertainty means, how precise the unit is defined in the S.I. and how stable it canmise-en-pratique, i.e. how well it can be realized and transferred to the "real" world.The Volt is defined to only about 0.2 ppm uncertainty in the S.I. (7 digits or 5 million counts)It can be realized by a Josephson junction array to an uncertainty of about 17 digits (comparison of two different JJ at cryogenic level), but it can be transferred to room temperature to 10nV noise level at 10V only, that is about 9 digits or 1 billion counts.Additionally, the best zener references yield about 0.2ppm stability, and the best analogue A/D is linear to 0.02ppm.Therefore, for DC voltmeters, 8 digits instruments will still stay useful, even if the planned updated S.I. will improve the volt definition to zero uncertainty in about 2018.For frequency meters, 17 digits are useful, as the current definition based on Cesium clocks is at first uncertain to that level, and ALSO can be measured and transferred at that level of stability.A MASER would serve as an intermediate reference at that stability level.Commercial counters display useful 12 digits at least, e.g. the famous HP5370B with 20ps/10 sec resolution, if it is fed by an Rb clock.Scientific systems, using an optical comb, may yield 18 digits in comparing two atomic clocks, but there is no commercial instrument available with that high resolution, afaik."Time" is the most stable physical unit, therefore the answer to your question as of today is "18 digits"Frank

author: dom0
author_rank: Super Contributor
timestamp: March 14, 2015, 10:30:32 am
content: Quote from: Vgkid on March 13, 2015, 11:18:32 pmIt's a perfectly valid number ; rather precisely 4 3/4 digits.

author: dom0
author_rank: Super Contributor
timestamp: March 14, 2015, 10:33:12 am
content: Quote from: Hydrawerk on March 13, 2015, 11:44:18 pm2000? The 3458A was released before the collapse of the east bloc. In 1989. 26 Years ago. Incredible...However, truth to be told, there were of course some product changes. But nothing major.

author: macboy
author_rank: Super Contributor
timestamp: March 14, 2015, 01:06:27 pm
content: Quote from: dom0 on March 14, 2015, 10:33:12 amYes, changes. Like the front panel HP logo being replaced by Agilent. Then the Agilent logo was replaced by Keysight.

author: Fungus
author_rank: Super Contributor
timestamp: March 14, 2015, 04:17:52 pm
content: Quote from: AG6QR on March 13, 2015, 08:31:33 pmWith this multimeter you could measure the electrical charge of the universe... then add a single electron and be able tomeasure the difference.That's quite impressive for a sub-$1000 instrument.(Not sure what you'd use as a ground reference, maybe your mom could volunteer...)

author: Rick Law
author_rank: Super Contributor
timestamp: March 14, 2015, 08:52:27 pm
content: Quote from: Dr. Frank on March 14, 2015, 09:30:26 amZero uncertainty? Hmmm... Now that becomes a matter of interpretation and/or definition. It can be zero uncertainty mathematically, but in practice we will be limited by quantum effects' domination at that level.It will be interesting to see how the world of science adept these physical phenomenons to push the accuracy ever far down.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 14, 2015, 11:31:07 pm
content: Quote from: Rick Law on March 14, 2015, 08:52:27 pmYep, itISa matter of definition, in the "new" S.I.The new definition will fix e (electron / elementary charge ) to an exact value , instead of an approximation by measuring it, and the same goes for h (Planck constant).Both constants of nature will afterwards have zero uncertainty, by definition.As a consequence, Volt and Ohm, both realized by the Josephson Junction and the von Klitzing Hall effect quantum devices, will also have zero uncertainty by this definition, as they then will bedefinedby combinations of e and h only, in the new S.I.As for every S.I. unit, you have to distinguish between itsdefinitionand itsrealization(mise en pratique)The realization isalwaysuncertain due to practical or physical limitations, as I've briefly described recently in this thread for the Volt..and practical uncertainty is much bigger than simply the Planck uncertainty limit.Anyhow, the advantage of the new S.I. is, that especially for the electrical units, we then will use for them quantum standards as primary standards, like already the Cs clock for time / second.Therefore, the practical realizations of Volt and Ohm already have been confirmed by comparison experiments, to be stable or uncertain to about 1E-17 .. 1E-19, so then being as "accurate" as the second.The problem remaining is, that you currently can't transfer this order of stability to the real analogue world. (in contrast to the digital time metrology)Precise analogue measurements will still be some sort of magic, so analogue magicians like Bob Pease, Jim Williams, Bob Widlar, Bob Dobkins, et. al. will still be urgently needed.Frank

author: photon
author_rank: Frequent Contributor
timestamp: March 15, 2015, 10:53:59 pm
content: Quote from: Dr. Frank on March 14, 2015, 11:31:07 pmWhat is the advantage of fixing the elementary charge to an exact value with infinite precision? Is this value going to change, say 20 years from now, when we have a better estimate from a device more precise than a Josephson Junction?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2015, 01:21:23 am
content: If it's defined as exact, there's no such thing as "more exact"!The sausage effect pushes the uncertainty onto other free variables. Those that are fixed by theoretical relations (like the characteristic of a Josephson junction) also have no uncertainty. Others (like G or k_B) limit the precision of related measurements.How about a color analogy? Suppose the primary and secondary colors are simply what people call them as; there's no theoretical or absolute definition of "red" or "cyan", they're just what people take them as.In this state, you know that, if you take about half and half proportions of the color called red, and mix it with the color called green (additive light here), you get what's called yellow.This is a simple, informal relation: R + G = Y. None of them are really quantitative, it's more like a Boolean statement.Suppose a Theory of Color is discovered, which fixes the values of R, G and B. And secondary colors are indeed proven to consist of primary colors. It is found that the color that's called "yellow" contains 57% R, 43% G. This proportion is now a measured quantity, in the same way that resistance is a measured ratio between voltage and current.Suppose the Theory of Color was later refined: it is discovered that, although the above is still true for additive lights, the exact opposite is true of subtractive pigments -- Y + C = G! And because of this, earlier standards which defined colors in terms of primaries only, but which had some bad tolerances (suppose, we can't get a good precise blue from incandescent lamps, so we've always had trouble building precise colors that contain blue), can now be defined in terms of pigments (which are now fixed fundamentals of chemistry instead).Incorporating some of these new definitions, suppose it is found that "common yellow" is 97.3% theoretical yellow, with a little bit of red thrown in. It's like redefining the inch in terms of the meter (1 in == 0.0254 m): it's slightly different from the accepted value, but close enough not to matter in many cases. With an exact correspondence, it no longer matters which format one uses to express their colors; it's just a matter of preference which color system they use.Now the state of things is such that, colors and mixtures are defined partly by lights and pigments; and that combinations of both can be used to get even more precise standards.Suppose the Theory of Color is proven complete. Now R, G, B and Y, C, F are fixed theoretical constants: the primary (light) colors are emissions at certain wavelengths, and the secondary (pigment) colors are absorptions at the same wavelengths. There is no longer any uncertainty whatsoever in the pure colors; and any color in the rainbow (or more importantly, that we can sense visually) can be expressed in any desired amount of precision.This is the future that physical standards aim for; whether it's theoretically possible (provable completeness) is still up for grabs. It is known that a certain limited set of physical constants (as measured parameters rather than fixed definitions) is necessary. Whether those are "top level" (spooky quantum parameters like h and c) or derived parameters (like the meter), doesn't matter to the theory, as long as the degrees of freedom are conserved.For more reading, check out alternative dimensional systems, like Planck units -- defining the fundamentals as unity (1.0 exact), and making customary units (like time and length) derived through proportions.Tim

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2015, 09:37:25 am
content: Quote from: photon on March 15, 2015, 10:53:59 pmThere are more changes to come: e, h, k and N(A) will get fixed values with zero uncertainty, and the units of mass, electrical current and the temperature will be defined differently.Especially, the IPK International Prototype Kilogram (an artefact body) will no longer be defining the mass.The advantage will be, that the physical units will be more based on constants of nature, and that the important units kilogram, Volt, Ohm, Ampère will have much lower uncertainty, in definition and also in realization.Quote from: photon on March 15, 2015, 10:53:59 pmThese then fixed values will very probably not change any more.First, the numerical values for e and h will simply be arbitrary definitions (to the best measured uncertainty as of today), like the speed of light and the length of the meter.Second, the definition of volt and ohm will be based on an elementaryphysical effect, independent from the material used to a very high degree of uncertainty.That is subtly different to the definition of the time , as this depends explicitely on the element Cesium, and today, there already exist more stable optical clocks (times 100), based on other elements.If you would change the definition of the second, you would also need a new fixed value for the new transition frequency.The uncertainty of today of Volt, Ohm (on the order of 2e-7) will be transferred into the definition and/or realization of other units or constants of nature, like epsilon(0) and µ(0).If these cross link measurements will be improved in the future, then the value and uncertainty for these other units will change, but not the volt or ohm themselves.There's a quite descriptive explanation of the change and its implications, especially see table 3:http://www.physics.usu.edu/dennison/3870-3880/Class_Notes/Lectures/Newell%202014%20PhysToday-SI%20Units.pdfand here similar FAQs on the BIPM site:http://www.bipm.org/en/measurement-units/new-si/faqs.htmlFrank

author: george graves
author_rank: Super Contributor
timestamp: March 16, 2015, 10:48:21 am
content: I'd guess that in order to measure a voltage, you have to draw a small amount of current, no? However small that might be. (if there is not current flowing at all, then the potential across the measuring terminals would be zero, no? Say you want to measure a tiny, tiny voltage. Lets assume it ssooooooooo tiny it's only 1 electron per second entering the meter.And since you can't have 1/2 and electron flowing, it has to be discrete and whole electrons flowing into the meter. So that's a whole number. 1, 2, 3 or 4 electrons.So at some point you would run into the limit of how few electrons were flowing through the meter at a given voltage. The lower the voltage, the less electrons.So I guess you could wait for X amount of time to count the flow of electrons....But voltage doesn't have anything to do with time? Or does it? Ok, now I confused myself.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2015, 11:12:10 am
content: Quote from: george graves on March 16, 2015, 10:48:21 amYou obviously confused that with the electrical current (Ampère), which is related to electrical charge.According to Maxwells equation, the "Volt", or to be precise, the electrical field does not need electrical charge!Also, Volt, Ampère and Ohm are three independent physical units, which are coupled by Ohms law.This indeed describes that the voltage over a resistor is linearily proporational to the charge rate flowing through it.In contrast, what you are describing, resembles the more intuitive Ampère definition by counting electrons per time.These devices already exist and are called SET, Single Electron Tunneling.If they were improved further, to give reasonable uncertainties, then an independent current standard will be available, based on the second.And then, the Metrological Triangle can be closed, that means it would be possible to check the validity of Ohms law with a high degree of precision:http://rsta.royalsocietypublishing.org/content/363/1834/2221.fullFrank

author: FrankBuss
author_rank: Unknown
timestamp: March 16, 2015, 11:22:06 am
content: Right, number of electrons is current, voltage isspeed of electrons. So I guess all you need would be one electron?

author: wiss
author_rank: Frequent Contributor
timestamp: March 16, 2015, 11:29:47 am
content: No, voltage is potential energy of an electron.

author: FrankBuss
author_rank: Unknown
timestamp: March 16, 2015, 11:38:28 am
content: A question to the physics experts here: is there a voltage quantization? This would define the maximum possible number of digits for a meter, which would even depend on the voltage range (if you measure a voltage near the quantization level, it would be just a few digits).

author: FrankBuss
author_rank: Unknown
timestamp: March 16, 2015, 11:41:25 am
content: Quote from: wiss on March 16, 2015, 11:29:47 amOk, what I meant was if you manage to let one electron flow from the voltage you want to measure with a sufficient high resistor, you could measure the speed of it and then calculate the voltage

author: george graves
author_rank: Super Contributor
timestamp: March 16, 2015, 11:41:34 am
content: Very interesting topic!Isn't voltage the potential to do work, and not work itself?But to measure voltage, you have to let it do some work - how ever small that could be. I'm reminded of my college courses where we would measure a static charge with a jar and two gold leafs attached to an electrode to the top of the jar. The fact the two gold leafs moved, means that work was done. So *some* current must have flowed. (pic below is only one gold leaf - but same idea)I understand you don't need current flow to have the existence of a difference in a potential, but to measure it, you must make it do *some* work. No? (or are we arguing the "observer effect"http://en.wikipedia.org/wiki/Observer_effect_%28physics%29Maybe I need to crack open my old text books. I think there is an analogy of the classic kinematic equations and electricity that might make more sense. In a derivative/integral sort of way.

author: HKJ
author_rank: Super Contributor
timestamp: March 16, 2015, 11:50:32 am
content: Quote from: george graves on March 16, 2015, 11:41:34 amNo.You use a adjustable voltage source and then measure the difference between the two voltage. When the difference is zero and no current is flowing, you can measure the adjustable voltage source and get the correct voltage without loading the original voltage.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2015, 11:57:18 am
content: Quote from: FrankBuss on March 16, 2015, 11:38:28 amThe electrical charge is quantized, i.e. the electron.Voltage is a potential difference, i.e. a field, and is not quantized.Electrical charge CAN create electrical fields and also magnetic fields, but both fields also exist without the presence of electrical charge, in the vacuum. That is called electro-magnetic radiation.Frank

author: george graves
author_rank: Super Contributor
timestamp: March 16, 2015, 12:00:43 pm
content: QuoteIsn't that using a ruler to measure a ruler?

author: dom0
author_rank: Super Contributor
timestamp: March 16, 2015, 12:10:34 pm
content: Quote from: george graves on March 16, 2015, 12:00:43 pmNo, it's how in the old times high impedance sources were measured. It's called a null-volt-meter and the main characteristic is that the input impedance is extremely high if the meter is zero.(You could call a precision supply and a null volt meter a voltage measurement bridge, if you want)(And the specific procedure he mentions is called a transfer-measurement. Note that this is one of the reasons there were precision supplies with decimal dials for voltage setting)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2015, 12:11:35 pm
content: Quote from: george graves on March 16, 2015, 10:48:21 amSo you're saying currents are magically quantized in units per second? What a magical constant this "second" must be.Current flow is not at all required to measure voltage; even the earliest galvanometers and bridges worked on this principle. When current is zero through a resistor, the voltages are equal on either side; therefore you have matched your test voltage to the reference.Even for a potential difference, current flow is not necessary; MOSFETs work just fine with a voltage difference and very little current flow. They are charge controlled rather than current controlled devices.Current flow need not be quantized in any magic "unit per time period" either; current can be perfectly continuous. Water doesn't magically pop through a hose, one end to the other, a molecule at a time; the position varies continuously with time, proportional to velocity.It's noteworthy that, on occasions where that DOES happen, electrons popping past a partition, through an energy barrier -- that tends to cause noise, specifically, shot noise. Partition noise in tetrodes and pentodes (old technology), for instance.There is, however, an electric current quantum. At least... I think there is? Maybe not... there is a magnetic flux quantum, which implies a nonzero ground state current. However, the amount of current depends on the inductance (and consequently, the dimensions and geometry) of the structure holding that flux quantum, so I think there need not be a fundamental current quantum at all. Which makes sense, as current is a continuous property.So, voltage is just a pressure or potential; you don't need any current to sense it, and it need not be quantized. Though you most likely need charge to perform the measurement (since the voltage sensor is made of material, which therefore has some capacitance), but that needs only a small transient current, not DC. And again, charge need not be quantized, because charge is carried by electron position, not just the absolute presence or absence of particles.A Josephson junction measures voltage proportional to time/frequency, so that the value can be counted in a quantized manner (discrete states of a frequency counter), but the parameter (voltage - frequency) is continuous.Tim

author: dom0
author_rank: Super Contributor
timestamp: March 16, 2015, 12:14:24 pm
content: Oh and just btw. the reason null volt meters are obsolete today is that any modern multimeter has >10 M? input impedance, which is good enough. Good meters will have an input impedance near their isolation impedance (G?) on the lower ranges.

author: FrankBuss
author_rank: Unknown
timestamp: March 16, 2015, 12:40:51 pm
content: Quote from: Dr. Frank on March 16, 2015, 11:57:18 amOk, but the electromagnetic field is quantized,says Wikipedia, doesn't this mean that voltage is quantized, too? The Planck constant is very small, maybe it would allow 20 digits meters in theory for the 1V range.

author: AndyC_772
author_rank: Super Contributor
timestamp: March 16, 2015, 12:42:07 pm
content: Interesting philosophical discussion...If our voltmeter is implemented as a bridge at balance, it's certainly true that no current flows, so the externally applied potential (ie. the potential being measured) should be unaffected by the presence of the meter.But then the question becomes, how do we tell when the bridge is balanced?The bridge is balanced when no current flows into or out of the meter. Current is charge per unit time, and charge is quantised.So, then it becomes a question of, how small a current is "no current"?If we wait for 1 second and count 0 electrons, is that "no current"? I'd argue that yes, for that 1 second period, there is indeed no current... but does that mean we can call the voltage measurement "exact"?What if we'd sampled the current for 10 seconds, and counted 4 electrons during that time? That's a current, so now we know our bridge is slightly out of balance. Perhaps we can adjust it slightly, and get a closer measurement. Ultimately, the precision we can achieve is limited by how long we're prepared to wait to see how close our bridge is to perfect balance.Remember also the definition for electric potential at a point in space, being the work done in moving a unit charge from infinity to that point. The charge may be quantised, but < flame suit > distance isn't </ flame suit >.

author: wiss
author_rank: Frequent Contributor
timestamp: March 16, 2015, 12:43:15 pm
content: Photons are quantized, there can be one or two or several.The wavelength of a photon is not quantized, it can be anything.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2015, 12:57:44 pm
content: Quote from: AndyC_772 on March 16, 2015, 12:42:07 pmSo you've answered your own question.Suppose we could observe electrons as they move through a wire (assuming absolute zero temperature, so no random thermal motion here). The drift of an electron, in an unbound state, need not be quantized (stepwise). Therefore, with suitable apparatus, we can detect currents arbitrarily close to zero, in arbitrarily small periods of time, limited only by the uncertainty principle (since the fields themselves fluctuate due to probability).Another way to think of it: the electric or magnetic field intensity might be quantized, but its position need not be.Some types of conductors do exhibit quantized (bucket brigade style) flow, such as solid ionic conductors (e.g., hot ZrO2 in fuel cells). These exhibit excess noise, corresponding to the mechanism, whereas simple metallic conductors exhibit very little excess noise (i.e., almost entirely Johnson noise).Tim

author: FrankBuss
author_rank: Unknown
timestamp: March 16, 2015, 01:02:16 pm
content: Quote from: wiss on March 16, 2015, 12:43:15 pmBut nobody knows if space itself is quantized, asloop quantum gravitypredicts. Then the wavelength would be quantized, too.

author: Fungus
author_rank: Super Contributor
timestamp: March 16, 2015, 01:03:20 pm
content: Quote from: AndyC_772 on March 16, 2015, 12:42:07 pmYep.What we call voltage is all about electron "pressure" - the desire of individual electrons to move to an area of lower electron density when there's electron overcrowding.This is relatedonlyto the distances between electrons. This makes voltage is a continuously varying value, it doesn't matter if the charge on the electrons is quantized or not.(nb. many languages actually call it "pressure", or "tension")

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2015, 01:05:12 pm
content: Quote from: FrankBuss on March 16, 2015, 12:40:51 pmNope. The Electrical field alone is not quantized!Photons are the quantized particles of the electromagnetic field, but these are a combination of electrical and magnetic field only.Additionally, these quantized photons can anyhow have any random value, simply change its wavelength or energy continuously..Whereas electrical charge - as far as we know today - is always an integral multiple of the Elementary Charge, i.e. the electron... there does not exist a fraction of e.Current is also not quantized, as time is not quantized, and Current is (the quantized) Charge divided by (continuous) Time, giving a continuous variable also.Frank

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2015, 01:13:50 pm
content: Quote from: Dr. Frank on March 16, 2015, 01:05:12 pmCharge need not be quantized, because net localized charge results from electron displacement -- which as you note, is a continuous variable. Likewise, the electric field (which is customarily in units of V/m, but the displacement field D = e_0 E is in units of coulombs -- analogous to the magnetic flux density field B = mu_0 H, if you aren't familiar with D) is not quantized, so it follows from both directions that charge need not be quantized either.The sources of charges -- the particles -- are necessarily, however. (Note that, strictly speaking, the most elementary charge is 1/3 its customary value, because electrically charged quarks are considered to have such fractional charges. This would make the electron charge 3e' (e' = e/3), but such a distinction is hardly worthwhile, so it hasn't been implemented.)Tim

author: Fungus
author_rank: Super Contributor
timestamp: March 16, 2015, 01:59:51 pm
content: Quote from: AndyC_772 on March 16, 2015, 12:42:07 pmYes, but it's perfectly possible for the average number of electrons passing through a wire per second to be 3.14159 ... or any other number you can imagine.The fact that electron charge is quantized doesn't tell you anything about volts or amps.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2015, 03:34:42 pm
content: Quote from: T3sl4co1l on March 16, 2015, 01:13:50 pmCharge may be continuosin theory , only. But all Physics rules and laws mandatory require experimental evidence.And this experimental evidence is one of the mysteries of physics, that charge in fact IS quantized.This would be explained easily if magnetic monopoles would exist, that means, if we could detect these experimentally.(To introduce them in the Maxwells Equations is as easy as theoretically assuming that charge is not quantized)With magnetic monopoles, this charge quantization would quite naturally follow.In (far) future Dark Matter and Dark Energy may be experimentally detected or explained, and then maybe also the existance of magnetic monopoles be postulated.Again, there is no fractional e ... in free particles:These Quarks, carrying -1/3e or +2/3e ALWAYS are bound inseparable together, so that always the discrete character of e is obeyed.All these high energy particles have absolutely no relevance for our practical, solid state world.Frank