Study On Drive Characteristics And Ways Of Coriolis Mass Flow Meter

Coriolis mass flow meter,which has the advantages of high measurement precision,good repeatability,multi-parameter and multi-fluid measurement,can measure the mass of the flow directly under many conditions.It is widely used in the petrochemical,food processing,pharmaceuticals and other industrial field.In this thesis,the problems,which arise in practical application of two drive systems of Coriolis mass flowmeter,are studied.The drive system is developed and drive method is proposed which can improve flowmeter drive performance effectively.For the problem that the flow tube stops vibrating based on analog drive system when the gas-liquid two-phase flow occurs,the reasons are analyzed.On this basis,the structure of the analog drive circuit is redesigned,and theoretical analysis and simulation is implemented.The analysis and simulation results show that new analog drive circuit can maintain flow tube vibration when the gas-liquid two-phase flow occurs,and it can ensure that the flow tube quickly returns to the optimum vibration amplitude when the gas-liquid two-phase flow disappears.The comparative experiments of driving characteristics between the old analog driving circuit and the new analog driving circuit are carried out,under continuous gas-liquid two-phase flow and flow pattern switching frequently.The experimental results show that the new analog drive circuit has better drive characteristics.For the problem that the flow tube has a large attenuation and overshoot of vibration amplitude based on digital drive system when single-phase flow and gas-liquid two-phase flow switch to each other frequently,the current control method is analyzed.,and then the variable drive cycle method and the variable integral-limiting-value method are proposed.Both of methods are realized in real time on the developed digital mass flow transmitter and verified experimentally.The experimental results show that the variable drive cycle method reduces the attenuation degree of the vibration amplitude effectively when the single-phase flow switch to the gas-liquid two-phase flow,and the variable integral-limiting-value method solves the significant overshoot of the vibration amplitude well when the gas-liquid two-phase flow switch to the single-phase flow.For the problem that the drive energy of the above two kinds of drive system is insufficient when the gas-liquid two-phase flow occurs or flow tube diameter is larger than before,the drive capacity of the current transmitter are analyzed.The analysis results show that the current transmitter has a larger enhancing space of the drive energy.Therefore,the differential drive mode is proposed.Compared with the single-ended drive mode,it can make the drive energy of transmitter doubled,and meet the requirements of intrinsically safe.The circuit is developed and used in Coriolis mass flow transmitter.The comparative experiments of two modes are performed under the gas-liquid two-phase flow,and the water flow calibration experiments are conducted.The experimental results show that the drive energy of transmitter is doubled,and the vibration amplitude of the flow tube is almost doubled when the transmitter is based on differential drive mode.Meanwhile,the measurement accuracy can still reach 0.1%in the case of the single-phase flow,so the differential drive mode has a great vibration stability.