Effects of the rotor obliquity on the cylindrical capacitive sensor

Abstract

The cylindrical capacitive sensor (CCS) is superior to conventional probe-type sensors in measuring the radial error motion of a rotor accurately since the CCS is immune to geometric errors of the rotor. However, due to the extended axial length of the CCS, the obliquity (or the axial tilt) of the rotor may cause unnecessary measurement error. This paper presents the effects of rotor obliquity on the performance of the CCS. The existing analytical model for the CCS has been extended to incorporate the axial tilt of the rotor, which leads to a new mathematical model for the CCS that can describe the complete three-dimensional motion of the rotor. Based on the new mathematical model, a nonlinear analysis is performed to derive the analytical solution of the measured rotor displacement with the CCS. As a result, it has been revealed how the rotor obliquity causes measurement errors in both eccentricity and phase angle. The analytical results are compared and verified with simulations.