An approach to mass measurement for the electronic balance based on continuous-time sigma-delta (CT    $\Sigma -\Delta $   ) modulator is described in this paper. As an effect of multifarious interfering noises, the accuracy of the electronic balance is restricted. The general idea of this proposed approach is to apply an electromagnetic-force-compensated load cell (EMCC), a related signal processing circuit, and a composite filter. The circuit mainly consists of a proportional-integral–differential controller and a pulsewidth modulator, which combine with the EMCC to form a CT    $\Sigma -\Delta $    modulator. As the CT    $\Sigma -\Delta $    modulator possesses inherent antialiasing filtering, oversampling, and noise-shaping characteristics, the interfering noises can be effectively removed by the composite filter that is composed of two    ${\rm sinc}^{N^{^{^{}}}}$    filters. The simulations for both of the electronic balance models adopting the proposed approach and working in conventional pulse current mode are analyzed by adding the white Gaussian noise in Simulink. The simulation results demonstrate the effectiveness of this proposed approach, the proposed electronic balance in the field can improve its signal-to-noise ratio, and the testing results meet the requirement for the weighing accuracy of the special-class scale defined by Organisation Internationale De Metrologie Legale R76 nonautomatic weighing instruments.
['Qiang Huang', 'Zhaosheng Teng', 'Xiang Tang', 'Haijun Lin', 'He Wen']
Mass Measurement Method for the Electronic Balance Based on Continuous-Time Sigma-Delta Modulator