The Driving System And Algorithm Research Of Coriolis Mass Flowmeter Based On FPGA

With the rapid development of modern industries such as the petroleum transportation and the trade of natural gas,there is an increasing demand for reliable and efficient measuring instruments for fluid mass flow.The Coriolis mass flowmeter can directly measure the quality of the fluid and its measuring sensor does not contact with the fluid and.Because of its advantages of high accuracy and good stability,the Coriolis mass flowmeter has widely attracted attention of the society and become a research focuses in Colleges and universities.Driving system is the precondition to ensure the regular work of flowmeter.However,it is slow that the traditional analog drive system drives the measuring tube to start vibration,which affects the flow meter to measure the mass flow rate of fluid.Therefore,aiming at the slow speed of the start vibration from traditional analog drive system of Coriolis flowmeter,this study analyzed the composition of the analog drive system.And the traditional analog drive system was improved by adding an amplitude control circuit to the rear stage of the automatic gain circuit,and a variable signal amplitude analog drive system of Coriolis flowmeter was developed.Compared with the traditional analog drive system,the proposed drive system improves the starting speed and system stability of the measuring tube.Although the analog driving method and circuit have been studied and improved,there are still some problems.The main drawbacks are: the analog driving circuit occupies a large space,there are more interference between components,and the amplitude of driving signal is unstable,and it is vulnerable to external environment interference.In this paper,we focus on the following research: use digital device FPGA instead of analog circuit to study the Coriolis Flow Meter digital drive system.On the basis of improving the principle of analog drive system,high-speed digital filter and digital AGC based on parallel signal processing of FPGA are studied to replace filter module and AGC circuit module used in analog circuit.The actual driving test shows that the starting time of the digital drive system is reduced to 3.6 seconds,and the anti-jamming performance is stronger than that of the analog driving system.The flow measurement of Coriolis flowmeter is mainly based on the two factors offrequency measurement and phase measurement of sensor signal.From the frequency measurement,the adaptive notch method,equal precision frequency measurement method and direct frequency measurement method are studied and analyzed respectively,and their advantages and disadvantages are obtained,and the adaptive notch is improved to reduce the frequency measurement error to less than 1 Hz.In the aspect of phase measurement,the Hilbert transform phase difference measurement method is studied,and the causes and distribution of Hilbert transform error under non-integer sampling are analyzed.According to the analysis results,the data under non-integer sampling are processed by adding window function,and then the data are periodicized to reduce the transformation error.The simulation experiment with MATLAB shows that the method can reduce the transformation error.The improved method improves the accuracy of phase difference measurement under non-integer period sampling.The trigonometric function operation is implemented in the FPGA using CORDIC algorithm,and the improved phase difference measurement algorithm is simulated and tested.In the process of flowmeter driving vibration experiment,it is necessary to observe the driving signal and sensor signal of flowmeter to determine whether the flowmeter has finished vibration.Therefore,a data acquisition platform based on C# is needed.Fluid-driven vibration test was carried out.