The unit that the electric resistance, measure with direct current, is the ohm (abbreviated Ω), named after the German physicist and mathematician Georg Simon Ohm (1789-1854). According to ohm’s law, the resistance R is the proportion of the voltage U across a conductor and the current I flowing through it:

Hence the follows: 1 Ω = 1 V/A. This meaning of the SI ohm is undoubtedly not viable for a realisation.

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Due to the especially reproducibility of the quantum hall resistance, that is perfect permanent stability and world-wide uniformity, the ohm can be realised as a certain fraction of the von-Klitzing constant. Currently since 1990, on basis of a referral by the CIPM (Comité worldwide des Poids et Mesures), resistance comparisons and also calibrations world-wide had to be referred to a resolved numerical value of the von-Klitzing constant, RK-90 = 25812.807 Ω90. The arrival of this conventional referral value because that the von Klitzing constant had considerable practical benefits in regards to maintainance and also dissemination the the unit ohm. At the exact same time, however, this also meant that the conventional unit Ω90 was not compliant through the worldwide System of units (SI) precious at the time. An SI-realization of the ohm was, e.g., possible with a Thompson-Lampard capacitor (calculable capacitance; because of the intricacy of the matching measurement setup, the achievable accuracies to be inferior come the reproducibility that quantum hall resistors.

On may 20, 2019, a review of the SI come into pressure according to which an SI value for the von Klitzing continuous RK = h/e2 can be derived using exactly identified values for the elementary fee e and the Planck continuous h. This do it possible to establish the ohm via the usage of quantum room resistors within the SI.

At, the resistance unit is realised from the quantum room resistance. Because that this purpose, our working team operates a cryostat v a superconducting solenoid. Come guarantee that the room resistance takes the exactly quantised value, some internationally accepted criteria need to be fulfilled . Firstly, the longitudinal resistance need to be zero due to the fact that a noodles longitudinal resistance is a measure up for finish quantisation (otherwise a correction has to be applied). Furthermore, all contact resistances that the quantum Hall an equipment have to be saturated small. Before every calibration, this criteria need to be proved experimentally. Moreover, the resistance values calibrated in ~ and at other nationwide metrology institutes need to be contrasted from time to time, to insurance a world-wide energy of the resistance unit ohm.

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for the dissemination of the unit, the turned out to it is in practicable come calibrate a standard 100Ω resistor with well-known drift behaviour about two times a year, utilizing a cryogenic present comparator. V this 100Ω working resistor, the calibrations because that’s client are brought out through Working group 2.11. Just in the case of distinct calibrations inquiry a relative uncertainty that 10-9 (or less), the resistor to be calibrated is directly measured against the quantum room resistance (i.e., without the intermediate action with the 100Ω resistor). An example is a precision measurement in ~ graphene in the framework of a study project.


Ensemble that 1Ω resistors indigenous "The Leeds & Northrup Co." as offered at previous times because that the conservation of the ohm.

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Head of Working team

Dr. Hansjörg Scherer


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