Coating Thickness Measurement Method Based On Eddy Current Technology And Digital Demodulation

The eddy current thickness measurement technology based on the principle of electromagnetic induction has high accuracy and sensitivity in the coating thickness measurement of various magnetized workpieces,and is widely used in aerospace,petroleum pipelines,industrial production and other fields.With the continuous development of technology,in order to meet the increasing accuracy of coating thickness measurement,this paper designs a combination of eddy current and digital demodulation technology for the measurement of coating thickness of non-metallic materials on metal substrates.measuring system.Specific research contents include the following:First,the current status of eddy current thickness measurement technology,theoretical models and simulation analysis.Several common coating thickness measurement methods are reviewed,and the current status of research on coating thickness measurement by eddy current method at home and abroad is introduced in detail from the aspects of coil probe selection,measurement signal characteristic value selection,and measurement data processing methods.Combined with the basic electromagnetic induction principle of coating thickness measurement by eddy current method,a transformer model of the measurement system was constructed and the corresponding theoretical analysis was performed.COMSOL Multiphysics software is used to establish a simulation model,design the preset conditions,analyze the measured data theoretically,and draw the theoretical curve of the coil voltage and lift-off distance.Second,a eddy current coating thickness measurement system and a core demodulation algorithm are designed.The hardware circuit includes symmetric low-noise differential circuit and excitation signal generation circuit,etc.the software program has completed the excitation signal generation including STM32 single-chip microcomputer as the core,sensor signal acquisition program,algorithm processing and serial communication program of upper and lower computers the design of.Among them,the algorithm processing uses a signal fitting algorithm based on digital demodulation technology.Compared with traditional hardware demodulation,the signal characteristic value is faster and the results are more reliable.Relying on the digital signal smoothing method of quadratic difference,the measurement signal is pre-processed to eliminate low frequency errors and further improve the measurement accuracy.Third,an experimental platform was set up to verify the measurement accuracy.The lift-off distance measurement is used instead of the thickness measurement of the coating.The displacement platform is used to move the lift-off amount by 10-500?m in a certain step,and the movement of the platform is measured in real time by using a grating.A variety of mathematical models are used to invert the measurement signals to obtain the amount of lift off,and the experimental results are compared with the theoretical values for comparison and error analysis.Experimental results show that the proposed detection method achieves a relative accuracy of less than ±3% in the measurement range,a resolution of 5 ?m,and high repeatability.Through the above-mentioned experimental research,combined with comparative experiments,the feasibility and reliability of a non-metallic coating thickness measurement system on a metal substrate based on the eddy current method based on digital demodulation technology were verified.