Estimation of Magnetic Coupling Factor from the Gap of an Eddy Current Probe

This work presents the evaluation of a method used to estimate the magnetic coupling factor and the lift-off from an ECT probe. Firstly, an electrical equivalent circuit is presented and mathematical models of the input impedance and input admittance are derived. Thus, a set of frequencies are chosen for stimulating the system, while the unknown parameters of the circuit, including the magnetic coupling factor, are identified with recursive least squares method. Simulations are conducted in order to evaluate the best set of frequencies, the sensitivity with respect to addictive noise in the input measurements of the impedance phase and magnitude and quantization of the sampling processing. Some preliminary results show that we can precisely estimate magnetic coefficients greater or equal to 0.2.