Electronics > Metrology

The years of resistance, volt and ampere definition / adjust

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Vtile:
Like title say, which were the years when atleast the Ohm did have a adjustment. Were it somewhere 1960? Other adjustment of the other unit are only "I think I have seen here mentioned".

floobydust:
I could not find a doc with the history of the fundamental constants. They seem to be revisited every 4 years, and updated as technology gets better. Next update is 2018.

Electrical Units in the New SI: Saying Goodbye to the 1990 Values (9/2014 paper):

"There will be an inevitable step change in the electrical units realized from quantum standards when this change is implemented, and the numerical values KJ-90 and RK-90 that have been in use for more than 20 years are abrogated and replaced by the new values of KJ and RK based on the latest experiments."

"The most significant effect is a step change of the order of 0.1 uV/V in voltage, as outlined in the previous section. High-end digital voltmeters have specifications of a few parts in 10^6.  Even though they behave better in the well-defined environment of a qualified (national)  metrology laboratory,  the effect of the step change will still remain unnoticed, swamped by the noise and instability of the internal Zener-diode voltage reference used in the instrument."

"a step change of 0.02u \$\Omega\$/ \$\Omega\$ in assigned resistor values due to the change from RK-90 to RK should only be seen on the top level working standards maintained within NMIs."

"Capacitance standards are often directly traceable to resistance standards, and in these cases will also see a step change of 0.02 uF/F on the introduction of the updated value for RK."

"We can expect this to change over the next few years, with the implementation of the new SI most probably occurring in 2018." 

Am I reading this right?  :-//

[edit: Greek alphabet is hell here]

Vtile:
I'm not sure.. I need to get some sleep, but I were more after the historic perspective. The ohm have got some tweak at some point and so is the voltage. I'm just wondering which year and what magnitude.. My google fu also end up with nothing. Just ascuired old L&N bridge, only 4 decades though, but I would like to calculate the effects as I assume it is specked with the old ohm.

I couldn't be the only one who have some museum instruments.  :)

Edit.. Or do I remember incorrectly as I can not find anything about ohm change.... Metrology institutions are so secretive (buried to scientific publications) about the basics. :)

Moon Winx:
Is this what you are looking for? http://www.bipm.org/en/publications/si-brochure/appendix1-electrical.html

Vtile:
Unfortunately that is only a partial answer. There is some / all of the years, but all I can substarct is that Josephon frequenzy is now 5000000 Ghz/V  |O I'm not metrologist (or even volt-nut ... yet), I would be happy just if the gray bearded scientists (in bipm or any other institution which maintains the SI system) would give a table that this and this decades units are x PPM smaller or bigger than the last decades units were and reason is Y.

.. Thank you for that link, I'm a bit closer again.

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