Research and implementation of amplitude ratio calculating system for Coriolis Mass Flowmeter

Coriolis mass flow sensor tends to be straight tube and micro bending tube with higher noise rejecting and less pressure loss, which results in the increase of the operating frequency, the difficulty in detecting phase difference and the calculation accuracy. Based on the current method of amplitude ratio calculation, the paper analyzes how the Coriolis Mass Flowmeter (CMF) closed-loop control system affects the amplitude ratio calculation, and presents a theoretical method with the amplitude of the driving signal participating in calculation. To achieve high-precision measurement of the amplitude, a comparative analysis by Matlab of curve fitting, correlation detection, windowed FFT detection in the case of signal amplitude fluctuation, frequency fluctuation and signal to noise variation, indicates that curve fitting is the suitable method to measure the signal amplitude. In the implementation of the system, a three-channel parallel data acquisition system is built to detect the CMF output signal. In order to eliminate the error brought by the differences between the channels, an automatic channel switching system is proposed to acquire the relative difference of each channel, then calibrate and calculate the flow signal of each channel. The preliminary experimental results demonstrate that the amplitude ratio calculating is available in calculating the mass flow rate of the CMF, with nonlinear error of 0.5% and repeatability of 0.6%.