The Absolute Measurement of the Ampere by Means of NMR

This paper describes the principle, apparatus, and uncertainties of the absolute measurement of the ampere by the nuclear magnetic resonance (NMR) method. A conversion factor between the as-maintained ampere of NIM and the absolute ampere is given by k = 1 -(5.81 ± 1.8) × 10-6 with a total uncertainty (1σ) of 1.8 ppm. Since two methods have been used to determine the gyromagnetic ratio in proton at the same laboratory, systematic errors of the as-maintained unit can be eliminated.