| It is had to obtain the thickness of heat insulating layer on the inside curved surface ofsolid rocket motors with a EC sensor calibrated on a plate, for it is hardly to be carried out thecalibration on the curved surface of the product directly. However, the influence of thecurvature of steel base on EC signal will cause larger error in thickness measurement. Smallervalue of the curvature radius will bring greater error. In this paper, influence of differentfactors on EC signal is studied through simulation and experiment to find the fitting curvemodel with smallest residual. The feasibility of application of an EC sensor calibrated on aplate to coating thickness measurement of curved shells is studied to obtain measurementresults with enough precision for the radius of the steel shell given and provideguidance in practice.First of all, various effects of EC signal strength factors is analysed through simulationfor choosing the size and parameters of the EC sensor for measuring larger liftoff distance.Influence of curvature radius and thickness of specimens is also studied. The best calibrationcurve model is found though a variety of curve fitting for simulation results.Secondly, the measurement results and errors for coating on the surface of the curvedspecimens with the plate calibration method are analysed through formula derivation, Basedon the analysis, the applicable range of the sensor with the plate calibration method is given.Finally, the experimental system for coating thickness measurement is set up and theliftoff distance is measured on the curved specimens. The error analysis of the measurementresults confirms the correctness of simulation results. |
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