The Analysis Methods for the Quality Factor of an Eddy Current Displacement Sensor

Abstract

The output voltage of an eddy current displacement sensor depends on the quality factor Q = ωL/R of the coil. Therefore, impedance analysis of the coil is important for output voltage analysis. Theoretical analysis of coils has been performed by C. V. Dodd, A. Reatti, and others. However, the quality factor of a coil cannot be calculated by using their theory. This paper presents theoretical, numerical, and experimental analyses of a coil for an eddy current displacement sensor. The impedance characteristics are analyzed by combining three theories: Dodd's theory, Reatti's theory, and the finite element method (FEM). As a result, the calculated value of the quality factor using the technique of complementing Dodd's theory with FEM is found to be accurate within seven percent. This technique is effective from the viewpoints of calculation time and accuracy. The calculation times of the three methods are also discussed in this paper.