Driving Method And System Of Coriolis Mass Flowmeter For Two Special Cases

Coriolis mass flowmeter, which can measure the mass of the flow directly with high measurement precision, good repeatability and meanwhile measure the volume, density, temperature of the flow in different fluid conditions, has broad application prospects. For two special cases, namely special flow tube and special measuring media, encountered in research and industrial applications of Coriolis mass flowmeter, driving system is developed and driving method is proposed to effectively resolve those problems.For the micro-bend or straight type Coriolis mass flow sensor outputs signal with high frequency and small phase difference, and the real-time processing of existing algorithms cannot be guaranteed in existing transmitter, a high frequency digital driving hardware platform of Coriolis mass flow meter is developed based on TMS320C6726. Resources are allocated reasonably according to the system functions and bus structure is used to overcome the shortage of DSP resources, common circuits and peripheral interfaces are expanded to realize instrumented functions, driving signal is synthesized digitally to maintain the flowtube oscillation in batch stream/two-phase flow. Electrical signal test results show that the measurement accuracy of the developed digital driving hardware platform reaches 0.1% for 1001 Hz signals with noise. And the experimental calibration results show that for Micro Motion DN25 caliber Ω type Coriolis mass flow sensor, the measurement accuracy is greater than 0.08% with the turn-down ratio of 11:1, and the repeatability reaches 0.03%.For Coriolis mass flow sensor outputs signal with large fluctuation, and optimal vibration amplitude of flowtube cannot be maintained in the process of industrial two-phase flow measurement, a variable sensor-setting-value driving control method is proposed. The factors affecting flowtube vibration amplitude and stability are analyzed, a variable sensor-setting-value control method is proposed to track the sensor amplitude variation, the comparative experiments of two kinds of setting-value methods are performed, standard deviation and PDF of two-phase flow signal are obtained to evaluated fluctuation characteristics. The comparative experimental results show that the variable sensor-setting-value method has a better performance both in signal tracking and amplitude controlling under the situations of different gas volume fractions and control responses. The flowtube can be maintained relatively stable vibration, and the fluctuation range of the sensor signal amplitude is small, which reduces the volatility significantly in the process of two-phase flow measurement.