Researches On Modeling Of Primary Meter And Amplitude Control Method Of Flowtube For Coriolis Mass Flowmeter

Coriolis mass flowmeter can measure mass flow-rate directly with high-precision, and is one kind of fast growing flowmeter currently. When Coriolis mass flowmeter, however, is used in a batching application or to measure two-phase (gas/liquid) flow, the damping of its flowtube increases quickly. The analog drive cannot maintain the flowtube oscillation in the fixed amplitude even stall the flowtube in these cases because of its limited drive gain and simple control algorithm.Digital drive is studied in this thesis in order to apply Coriolis mass flowmeter to the batching situation and measurement of two-phase flow. Firstly, the time-varying mathematical model of the primary meter is set up for Coriolis mass flowmeter. The parameters of the model of CNG050 type primary meter made by Micro Motion, Inc. are determined through the experiments of analog drive and the simulation of Simulink. Secondly, the non-linear amplitude control algorithm used for digital drive is studied and an improved solution is put forward, i.e. a variable proportional control is added in the non-linear amplitude control algorithm. According to the two-phase flow experimental data from Oxford University, the damping ratio change pattern is deduced to reflect the process of two-phase flow. The amplitude control algorithm of flowtube is validated by the Simulink simulations and experiments. The results show that the improved non-linear amplitude control algorithm can raise the start-up speed of oscillation of the flowtube and maintain the flowtube operation even in highly damped conditions. Finally, two types of waveform synthesis methods are studied to control the vibration amplitude of the flowtube in full digital mode.