Noncontact High-Resolution Stress Measurement Based on Resonance Eddy Current Technique

Non-contact measurement techniques yield lower resolution, thus limiting their application in fields requiring high-precision stress measurement, such as the measurement of stress variation in pipelines during peak shaving operations at thermal power stations. The present paper proposes a non-contact, high-resolution stress measurement method based on the series-parallel capacitor-coordinated resonance eddy current (R-ECT) technique. A theoretical analysis was conducted to examine the manner in which capacitors regulate the stress sensitivity of resonance frequency and impedance. Therefore, the stress response sensitivity of R-ECT can be amplified. In addition, the employment of a vector network analyzer was undertaken for the purpose of narrowband filtering, with the objective of attenuating noise. It is evident that these factors contribute to an enhancement in the measurement signal-to-noise ratio and stress measurement resolution. The experimental investigation conducted on the silicon steel sheet stretching machine demonstrated that the proposed model exhibited a maximum prediction error of 1.48% and 13.72% for the stress response sensitivity of resonance frequency and resonance impedance, respectively. The experiment also demonstrated that the R-ECT probe, which had been designed with high-frequency and high-sensitivity specifications, was capable of achieving a stress measurement resolution of less than ±1.72MPa (less than 3.52% F.S., resonance frequency) and less than ±2.78MPa (less than 5.69% F.S., maximum point of the magnitude-frequency curve).