Design Of Excitation Control System For High-frequency Electromagnetic Flowmeter Based On Switching Power Supply

An electromagnetic flowmeter is a type of tool that measures the volume flow of conductive liquid based on Faraday's law of electromagnetic induction.Due to its simple structure,corrosion resistance,and reliable performance,it is widely used in the industry processing control.At present,the electromagnetic flowmeters of domestic manufacturers mainly use the low-frequency rectangular wave excitation method,which limits the response speed of the electromagnetic flowmeter and cannot measure the slurry fluid.Therefore,a new electromagnetic flowmeter excitation control system needs to be designed to improve the excitation frequency and excitation current accuracy,reduce the power consumption of the excitation system.In this thesis,the excitation system based on high-frequency rectangular wave is designed.In view of the problems of high power consumption,high temperature rise,short excitation steady state,and large current ripple in the high-frequency rectangular wave excitation,the following work is done:(1)In view of the problems of high power consumption and temperature increase of the electromagnetic flowmeter power supply system,a flyback switching power supply system is designed to improve the efficiency and energy density of the power supply system,reduce the system temperature rise,and broaden the electromagnetic flowmeter operating temperature.(2)In order to resolve the serious heating problem of the excitation control system based on the linear power supply,the optimization excitation control system is designed,and the constant current control circuit is based on the switching mode power supply PWM modulation.The efficiency of the constant current source circuit is improved,the power consumption and temperature rise of the excitation system is reduced.(3)Aiming at the problems of slow response speed and low light load efficiency of the PWM modulation excitation control system,an excitation control method based on PFM modulation is proposed.The principle of PFM constant current control is analyzed,the scheme of the excitation control system is given,the excitation control system of PFM modulation is developed and applied to the electromagnetic flowmeter transmitter,and the water flow calibration experiment is carried out.The results show that the PFM modulation excitation control system improves excitation frequency and constant current source efficiency,achieves 0.5-level accuracy in water flow calibration experiments.