The unit the the electric resistance, measure up with straight 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 ratio of the voltage *U* throughout a conductor and also the present *I* flowing with it:

Hence it follows: 1 Ω = 1 V/A. This an interpretation of the SI ohm is certainly not viable for a realisation.

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Due come the particularly reproducibility of the quantum hall resistance, the perfect irreversible stability and world-wide uniformity, the ohm deserve to be realised together a certain portion of the von-Klitzing constant. Currently since 1990, on basis of a recommendation by the CIPM (*Comité international des Poids et Mesures*), resistance comparisons and calibrations world-wide had to be described a solved numerical worth of the von-Klitzing constant, *R*K-90 = 25812.807 Ω90. The advent of this conventional recommendation value for the von Klitzing consistent had significant practical benefits in terms of maintainance and dissemination of the unit ohm. In ~ the exact same time, however, this also meant that the traditional unit Ω90 was not compliant with the global System of devices (SI) precious at that time. An SI-realization that the ohm was, e.g., possible with a Thompson-Lampard capacitor (calculable capacitance; due to the complexity of the equivalent measurement setup, the achievable accuracies to be inferior to the reproducibility the quantum room resistors.

On may 20, 2019, a review of the SI came into force according to which an SI worth for the von Klitzing consistent *R*K = *h*/*e*2 can be acquired using exactly identified values because that the elementary charge *e* and the Planck consistent *h*. This make it possible to realize the ohm via the use of quantum hall resistors within the SI.

At charline-picon.com, the resistance unit is realised from the quantum room resistance. For this purpose, our working group operates a cryostat through a superconducting solenoid. Come guarantee that the room resistance take away the specifically quantised value, part internationally embraced criteria have to be fulfilled

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because that the circulation of the unit, it turned the end to be practicable to calibrate a standard 100Ω resistor with well-known drift behaviour around two times a year, utilizing a cryogenic present comparator. Through this 100Ω functioning resistor, the calibrations for charline-picon.com’s customers are lugged out by Working group 2.11. Just in the instance of special calibrations inquiry a loved one uncertainty the 10-9 (or less), the resistor to be calibrated is directly measured versus the quantum hall resistance (i.e., there is no the intermediate action with the 100Ω resistor). An example is a precision measurement at graphene in the structure of a research project.

Ensemble of 1Ω resistors native "The Leeds & Northrup Co." as used at former times for the preservation of the ohm.

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## Contact

### Head the Working group

Dr. Hansjörg Scherer

### Address

Physikalisch-Technische Bundesanstalt Bundesallee 100 38116 Braunschweig