Principles of the Kibble Balance

Abstract

In order to calibrate an electricity meter, is mandatory get a reference standard within known, accurate and accessible specifications. The reference standard used before 2018 was a platin-iridium mass. Currently this reference is a multiple of the Plank constant, achieved by using a Kibble balance. The first step in building the balance is to find the constant (with an analytical approximation) of linearization of the coil that generates the magnetic force of the balance. The electric current flowing through a coil generates a magnetic force that will keep a small reference mass in equilibrium with a mass to be measured. On the other hand, to calculate the mass, due to the analytical imprecision of this constant, it must be eliminated. For this purpose, two measurements will be made in two different modes of the balance. A current (A) measurement in “weight mode” or “balance mode”. The second measurement, of voltage (V), in “speed mode” or “calibration mode”, in the latter, without the reference mass. The constant is common in both measurements and equations. The two equations are equal to this constant, so this constant is eliminated. Knowing the value of gravity, speed, the value of mass can be calculated without that analytical inaccuracy of the constant. The prototype was built and installed at the Eletromagnetism Laboratory of IPUC; it is available to the academic comunity and it proved to be relevant also in carrying out experiments in the Basic Education (High School) classroom, vhich worked as a pilot to verify the potential of the discoveries hightlighted here.