Volt balance realization of the volt at ETF in Zagreb

Abstract
A volt balance having plate electrodes operating in a temperature-controlled atmosphere of dry nitrogen is described. The voltage is measured by a special procedure of substitution of a weight for the electrostatic force, with automatic control of the balance equilibrium. This, together with the application of very sensitive capacitive transducers for measuring the balance equilibrium and electrode displacements enables a weighing reproducibility of less than 0.1 ppm to be achieved. The earthed electrodes are suspended over the beam arms by means of two thin strips separated one from the other in such a way that optimal sensitivity to the existence of horizontal electrostatic forces is achieved. Through the remote adjustment of the horizontal position of the high-voltage (H-V) electrodes, and by measuring the displacement of the suspended and H-V electrodes, it is possible to eliminate horizontal electrostatic forces. The displacement of the H-V electrodes by 51 mm (corresponding to a capacitance change of 100 pF) enables highly precise capacitance and length measurements to be made. The third improved version of the Zagreb Faculty of Electrical Engineering (ETF) volt balances is now being completed. The mean result of six measurements obtained with two earlier balances indicates that the difference between the International System (SI) volt determined by the ETF volt balances and volt BI-76 is +7.1 ppm with a random one-standard-deviation (1σ) uncertainty of 0.4 ppm and a systematic 1σ uncertainty of 1.6 ppm.

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