Abstract：The Joule balance method is one of the methods to redefine and realize the kilogram based on the Plank constant. Considering the unideal initial position and gesture of the suspended coil, it hard to achieve an ideal balance between the electromagnetic force and weight gravity, and then alignment errors are produced. It is one of the largest uncertainty sources in the Joule balance. Based on the mechanism of the alignment errors and combined with mechanical and electromagnetic properties of the Joule balance, the model between the initial position and gesture of the suspended coil and its parasitic displacements is build up and analyzed. The theory will lay the foundation of restraining the alignment errors.
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