Research On Dual-frequency Eddy Current Displacement Sensing Technology

Measurement is the use of a certain tool to achieve an objective understanding of the target.With the advancement of science and technology,the measurement of highprecision and micro-displacement has become crucial,and the requirements for measuring instruments have become higher.The eddy current displacement sensor is a measuring instrument that can perform non-contact and high-precision measurement.It mainly uses the electromagnetic mutual inductance effect to work.It can adapt to complex measurement environments and has strong anti-interference ability.The current research on eddy current sensors mainly focuses on the performance improvement of single-frequency displacement measurement and the signal processing of multi-frequency flaw detection.This thesis mainly studies the dual-frequency excitation eddy current displacement sensor,and eliminates the influence of temperature on displacement measurement through the dual-frequency decoupling operation.The relationship between the impedance of the eddy current displacement sensor probe coil and the structure is analyzed in the thesis by COMSOL's simulating function,and the changing rules of the coil impedance with its structure are obtained.Then the structure of the probe coil is determined based on the rules.Through the dual-parameter scanning of COMSOL and the data fitting function of MATLAB,the combined relationship of coil impedance with displacement and temperature is obtained.This is the theoretical basis for the dual-frequency eddy current displacement sensor to eliminate the influence of temperature on displacement measurement.Secondly,the design of the dual-frequency excitation signal source is completed in the thesis.Dual-frequency mixed signal is generated by MATLAB and DDS(Direct Digital Synthesis)and the parameters are optimized through the waveform simulation.The way of using MATLAB to generate signal data and DDS to output the signal can simplify the generation of complex signal,which can also save hardware resources.In the test phase,a band-pass filter circuit is used to improve the signal source and improve the quality of the output signal.Finally,that the dual-frequency eddy current displacement sensor eliminates the influence of temperature on the displacement measurement is verified in the thesis and the simulation design of the signal processing circuit of the dual-frequency eddy current displacement sensor is completed,which mainly includes four parts.Firstly the multistage amplification circuit is designed for weak signals.Corresponding to different resolutions and ranges,different magnifications can be achieved.Secondly the bandpass filter circuit for dual-frequency signal separation can effectively separate the single-frequency signal from the mixed signal.Thirdly the phase shift circuit is designed for the output signal of the AC bridge.The output signal of AC bridge is amplified and filtered before the phase-sensitive detection.In order to ensure the precision and accuracy of the phase-sensitive detection,the output signal of the bridge needs to be phase-compensated.Fourthly the phase-sensitive detection and low-pass filter circuit are designed to extracted the DC component in the AC signal which can reflect the displacement.