How is calibrated a 8.1/2 digits multimeter without any 9.1/2 digits multimeter? - Page 1
Forum section: electronics / general

author: myf
author_rank: Regular Contributor
timestamp: September 24, 2018, 04:41:02 pm
content: Hello,I understand that a (n + 1) digit multimeter can calibrate an n digit multimeter.It is also possible to compare 2 or 10 identical multimeters to keep only those whose measurements are close to the average.If we assume measures with Gaussian noise and Gaussian errors, an average of 100 measures adds a number to this measurement. But is there any proof that these errors are really Gaussian ?On the other hand, it appears that Zener reference voltage chips can not be more accurate than 0.01% = 1e-4. The electronic junction voltage is not so fixed and changes slightly around 1e-4. Two identical chips don't have the same tension. tension varies.So how can agilent, hp, keisight and other main factories can built and calibrate 8digits multimeters? It's easy to get a 1.59V (+/-1e-2) reference tension on any alcaline battery. But how can we build and control a 1.00000000 (+/- 1e-8) V reference tension ? It seems almost impossible to construct the international definition of 1Volt with a very small error.F. (from France), very curious but without knowledge in metrology

author: MiDi
author_rank: Frequent Contributor
timestamp: September 24, 2018, 04:52:55 pm
content: Josephson Junction arrays (primary standards) are an order of magnitude better than best meters.Than there will be the step to secondary standard as e.g. Fluke 732B.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 24, 2018, 04:58:29 pm
content: Quote from: myf on September 24, 2018, 04:41:02 pmMaybe the link below will help you. Ultimately the voltage isn't derived from a zener diode. "The quantum accuracy of these voltages is derived from the Josephson Effect such that every superconducting Josephson junction in the PJVS circuit produces a voltage precisely proportional to the frequency of the applied microwave bias signal."https://www.nist.gov/sri/standard-reference-instruments/sri-6000-series-programmable-josephson-voltage-standard-pjvs

author: tggzzz
author_rank: Super Contributor
timestamp: September 24, 2018, 06:35:07 pm
content: This is a principal issue with metrology; just how do you test the best (i.e fastest, most stable, least noise, most precise, most repeatable, etc) measuring equipment?Or for, that matter, the fastest oscilloscopes such as the newHPKeysight 256GS/s scope.Answer: you use skill and imagination, but they are not common. (See my .sig)Those attributes are also very useful for hobbyists and professionals.Hence I have little time for those that say old equipment is useless; used with imagination they can be remarkably good. Example: at school we used to 2% voltmeters to measure voltages to 0.1% using a NiFe cell, a standard cell, a 1m piece of wire, and a 1m ruler

author: SilverSolder
author_rank: Super Contributor
timestamp: September 26, 2018, 12:43:57 am
content: Quote from: tggzzz on September 24, 2018, 06:35:07 pmI had to think about that one for a while! - did you lay out the piece of wire along the ruler, and use its resistance and the ruler scale as an extra digit?

author: tggzzz
author_rank: Super Contributor
timestamp: September 26, 2018, 07:26:13 am
content: Quote from: SilverSolder on September 26, 2018, 12:43:57 amThat's the start..The Weston standard cell is a known accurate voltage (1.0186V) but you must take zero current. It cannot power the resistance wire.The NiFe cell has a reasonable stable voltage (~2V) and can supply current sufficient to power the resistance wire.So you use a cheap 2% voltmeter in series with the Weston cell, and probe along to find the position on the wire where the voltmeter reads 0V (+-2%). At that point no current is drawn and voltage on the wire is 1.0186V. From there it is a simple matter that ratio-of-distance = ratio-of-voltage.Professional equipment of the time contained a KVD, a null-voltmeter and optionally a standard cell.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 26, 2018, 07:12:40 pm
content: I suppose no lab is complete without a Leeds & Northrup Type K potentiometer-http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Potentiometer/Potentiometer.htmlThe wire is wound on the drum.

author: iMo
author_rank: Super Contributor
timestamp: September 26, 2018, 08:26:21 pm
content: https://xdevs.com/doc/HP_Agilent_Keysight/3458A/03458-90017_Ed6.pdfThey did it at factory the same way, I bet..

author: ap
author_rank: Frequent Contributor
timestamp: September 26, 2018, 08:30:56 pm
content: Generally speacking the trick is not using skills or imagination but math. At least when using calibrators for equipment calibration.The method that is used is called guardbanding. Given the uncertainties are mostly following the gaussian distribution, if the test uncertainty ratios (TUR) between device under test and standard are not good enough, in a nutshell, one narrows down the acceptable deviation of th DUT. Details are e.g. given in fluke app notes covering the 5720/5730. These usually are not precise enough to calibrate the 3458a as-is.The other option is to not use a calibrator but dedicated standards. These can be maintained in a much better uncertainty than a precision calibrator. This is more time consuming as it is a manual process, but gives better results (lower uncertainty).

author: myf
author_rank: Regular Contributor
timestamp: September 28, 2018, 03:34:16 pm
content: Hello,Many thanks for your answers !I discover link between the time [in second] and the tension [in Volt] by the constant h/e in Josephson experience.During tast century, Weston cell is less precise but easier to understand.I see some Weston cell on ebay.com. The last issue is the article number for searching in ebay.at 40eur :http://www.ebay.fr/itm/EPPLEY-Weston-STANDARD-CELL-Vintage-EPLAB-for-VOLTMETER-CALIBRATION/202429410316at 60eur :http://www.ebay.fr/itm/Weston-Model-4-Vintage-Standard-Cell/183329131420Do you think theses cell can still provide the right voltage ? or are they broken ?Is it safe to have such a cell with toxic cadmium and mercury at home ?But I will prefer a ad586 circuit...Other tests are possible and accurate with ratio-of-distance = ratio-of-voltage.How precise can be theses methods ? 1e-3=10^-3 with errors about 1mm for 1m ?Have a nice day !F. from France.

author: tggzzz
author_rank: Super Contributor
timestamp: September 28, 2018, 08:06:56 pm
content: Quote from: myf on September 28, 2018, 03:34:16 pmThere are two types: fragile saturated and less fagile unsaturated.The saturated cells should be kept upright so the crystals aren't dislodged.https://entertaininghacks.wordpress.com/2016/12/28/a-weston-standard-cell-an-introduction-to-voltnuttery/You can search for other threads on this forum.QuoteYes, provided nothing is broken.Getting it to and from the home is a different issue, especially since carriersreallydon't like transporting mercury nor cadmium. If Hg gets loose in aircraft it can seriously weaken the Al structureOf course you shouldn't simply throw them in the rubbish bin, but dispose of them safely.QuoteAt school we used a 1m ruler/wire with 1mm divisions. You could use longer wires or have finer divisions

author: branadic
author_rank: Super Contributor
timestamp: September 28, 2018, 08:11:23 pm
content: QuoteWell, you send in a two years old, fully working 3458A to Keysight for calibration and get it back with error 110 and error 205-branadic-

author: guenthert
author_rank: Frequent Contributor
timestamp: September 29, 2018, 07:27:48 am
content: Quote from: myf on September 28, 2018, 03:34:16 pmSaturated standard cellscan potentially, when always properly cared for, beverystable. They are howeververyfragile (must never be turned upside down, must never be exposed to overcurrent, etc.). They hold only a small charge and hence must not drive high loads. It is even recommended not to measure them directly with (even 'high' impedance) multimeters. You measure them exclusively using the potentiometer method. Their output voltage depends fairly strongly on temperature, hence they can be sensibly used only in temperature stabilized enclosures.Unsaturated cells haven't been produced to my knowledge in the Western World for decades. They lose their charge over time and all you will be able to find have drifted out of specification. They are a mere (toxic) curiosity at this time.Quote from: myf on September 28, 2018, 03:34:16 pmIf you have to ask, then the answer is a resoundingno.Quote from: myf on September 28, 2018, 03:34:16 pmYes, I'm sure you do.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 29, 2018, 04:44:29 pm
content: Quote from: branadic on September 28, 2018, 08:11:23 pmWhat?