Development of a Compact Magnetic Suspension Balance

Abstract

This article develops a prototype of magnetic suspension balance (MSB) for mass measurement, in which the mass of the sealed sample is transferred to the measuring unit via the magnetically suspended method. Considering that the excitation current decides the magnetic force while the magnetic force balances the gravity of the detected object, a type of compact MSB can be obtained by combining the force sensor unit and the magnetic suspension coupling unit (MSCU). Many efforts are undertaken to improve the performance of the compact MSB. The design parameters of the MSCU are optimized to decrease the sensitivity of the magnetic force to the variation in the suspension height; the magnetic suspension system is regulated by an active disturbance rejection control method to decrease the current fluctuation in the stator coil; the calibration method founded on the least-squares method is used to suppress the data drifts existed in the measuring process. The testing results show that both the resolution and repeatability of the MSB reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500~\mu \mathrm {g}$ </tex-math></inline-formula> , and the measuring uncertainty is less than 1 mg for the weights up to 1 g.