Research And Development Of Low Frequency Magnetic Field Measuring System

With the continuous progress of science and technology,people have more and more in-depth research on magnetic field,and the application demand of magnetic field measurement is also expanding.Based on the practical application demand of low frequency magnetic field measurement in railway field,a low cost measuring system is designed and developed,which can get the frequency spectrum of low frequency magnetic field(40Hz～20KHz).The main work of this thesis is as follows:Firstly,according to the design requirements,the hardware composition of the system is determined by hardware comparison.The measuring system consists of the coil as a magnetic field sensor,PC as the upper computer,digital oscilloscope as the lower computer,in order to achieve the low-cost requirement and spectrum analysis application.Secondly,the software of the measuring system is designed and written by using C# programming language.The software adopts the modular design concept,which consists of four parts: communication module,acquisition module,storage module and FFT module.The data connection between PC and oscilloscope is realized by using communication module.With the aid of the acquisition module,the setting and inquiry of various parameters of oscilloscope are completed.For the storage module,on the basis of the acquisition and display of the signal by the control oscilloscope,the data of the waveform can be transmitted to the PC and saved.The conversion of the coil induced voltage signal from time-domain waveform to spectrum is realized by means of FFT module.Thirdly,the calibration method of frequency response curve of sensor coefficient of measuring coil is studied.Firstly,a new experimental method is proposed.The measuring system is built,and the transduction factor of the coil is obtained by experiments.Next,the theoretical calculation of the coil transduction factort is completed based on Faraday electromagnetic induction law.Then,the simulation results of coil transduction factor are obtained by COMSOL simulation.Through the comparison and analysis of the results obtained by the experiment,theoretical calculation and simulation,according to the advantages and disadvantages of the three methods in different frequency bands,the frequency response curve of the measuring coil in the whole test band is determined by using the method of segmented splicing.Fourthly,completed the test and verification of the system.In the laboratory environment,the magnetic field is generated by the Helmholtz coil,and a calibrated Tesla meter is used to measure the magnetic field.Compared with the magnetic field measured by the system in this paper,the relative error of calculation is less than 5%,which proves that the system in this thesis can achieve relatively accurate measurement.The thesis includes 26 pictures,13 tables and 40 references.