LVDT Measurement Accuracy Analysis And Compensation Method Research For Triaxial Tester

Liner Variable Differential Transformer(LVDT)is widely used in high precision control and detection field due to its excellent performance and good environmental adaptability.LVDT is used to measure the deformation displacement of rock in different states in triaxial apparatus.Its output accuracy determine the measurement accuracy of the triaxial tester.However,LVDT has disadvantages of poor linearity and low sensitivity in the application of triaxial test instrument,which reduces its output accuracy.Therefore,it is of great significance to study the structural characteristics of LVDT to optimize the output accuracy of LVDT itself and the accuracy of output data of triaxial apparatus.In this paper,the electromagnetic performance of LVDT with triaxial instrument is analyzed and studied by using ANSYS Maxwell and Maxwell Circuit Editor.The equivalent electromagnetic finite element model of LVDT is established in Maxwell,and the setting of the external excitation Circuit is completed in Maxwell Circuit Editor.Import the set external circuit into Maxwell for coupling simulation to obtain the simulation output.Build the experimental platform of differential transformer type displacement sensor,and manufacture prototype for the experiment,then we obtain the output results under actual working conditions.The analysis of the results shows that the output data of simulation is basically consistent with the output data under actual working conditions,proving the feasibility of the scheme.In view of the influence of external environment,such as external magnetic field,external temperature field and excitation frequency,on LVDT output accuracy during the operation of triaxial tester,study the reasons,and propose the corresponding compensation optimization scheme.Aiming at the problem that the output accuracy of LVDT becomes worse due to the structural characteristics,the corresponding structural innovation scheme is proposed to compensate the magnetic field.Magnetic compensation scheme formulates "end cover" and "coil" magnetic compensation scheme?The "end cover" magnetic compensation scheme is for the first time to apply the electromagnetic shielding principle in LVDT internal structure design,design of multi-layer end cover to replace the traditional single end cover,divided into inner,middle and outer three layers,the new end cover structure significantly reduce the LVDT end magnetic flux leakage phenomenon,the "end cover" magnetic compensation scheme can make the maximum linearity 2.33% down to 0.15%,15 mv/mm sensitivity to ascend;"Coil" magnetic compensation scheme refers to the addition of two symmetrically distributed secondary coils at the lower part near the end cover to make up for the weak magnetic field at the end.The "coil" magnetic compensate scheme can reduce the maximum linearity from 2.33% to 0.41% and increase the sensitivity by 240mv/mm.On the basis of this,Analyze the influence of inner cover thickness on LVDT output precision in the magnetic compensation scheme of the "end cover",the optimal thickness of each end cover is determined.According to the magnetic compensation scheme of the "coil",the installation position and turns number of the compensation coil are studied,and the optimal installation position and turns number of the compensation coil are found.Finally,Summarize the research on the precision analysis and compensation method of LVDT with triaxial instrument,then propose the research direction for the next stage according to the existing shortcomings.