Research On Electromagnetic Flow Measurement Technology Based On Dual-frequency Excitation

Electromagnetic flowmeter is widely used to flow measurement for conductive fluid in industrial and agricultural production,which is based on the features that it's measuring accuracy is not affected by the density,viscosity,temperature,pressure,and change in conductivity within a certain range of the fluid medium and no pressure losses because there is no component which could obstruct fluid flow in the measuring tube.With the continuous expansion of the application field of electromagnetic flowmeter and the continuous development of excitation technology,high-end incentive technology represented by dual-frequency excitation technology has been emerged.This technology combines the advantages of excellent zero stability of low-frequency excitation technology and high-frequency excitation technology with high response speed and strong ability to suppress slurry interference.However,the core of this technology is monopolized by foreign companies,and domestic research data are scarce,therefore,the research on dual-frequency excitation technology is of great significance.Firstly,this thesis mainly studies the electromagnetic flowmeter measurement theory and weight function theory,then,using COMSOL finite element analysis software to optimize the structure of the saddle-shaped coil,finally,the output signal model of the electrode and the dual-frequency excitation technology are studied.Based on the previous theoretical and simulation studies,the hardware and software design of the dual-frequency excitation electromagnetic flow measurement system with the TMS320F28335 digital signal processor as the core is implemented,and a flow signal processing and extraction method for the output signal of the dual-frequency excitation electrode is proposed.The system hardware mainly includes electromagnetic flow transducer design and dual-frequency constant current source excitation circuit,flow signal detection and processing circuit design,system software to achieve electrode output signal filtering,flow signal extraction algorithm and the entire system monitoring.In order to verify the feasibility of the designed dual-frequency excitation electromagnetic flow measurement system,a flow verification experiment platform with a standard table comparison method was set up for experimental testing.Through clean tap water flow verification experimental test,the system matched self-made 110-caliber electromagnetic flow transducer.When the flow measurement range is(9?90)m3/h,the maximum relative error of the system is 0.9%,and the system's response speed is about 4.7s.In order to demonstrate the superiority of dual-frequency excitation in slurry flow measurement,a comparative experiment of slurry was conducted.The test results show that the ability of the system to suppress slurry interference is better than the ordinary low-frequency excitation electromagnetic flowmeter on the market.This technology can also be applied for the design of electromagnetic flowmeter in the future.