A cylindrical capacitive sensor (CCS) for both radial and axial motion measurements

Abstract

Conventional cylindrical capacitive sensors (CCS) are used only to measure the radial error motion of rotating machinery. However, axial error motion is also very important in rotating machines and it is very difficult to measure the axial motion due to the limited space. This paper presents a new CCS for both radial and axial motion measurements. The idea behind the new sensor is that the unused axial area of the CCS is exposed to measure the axial motion of a target. A theoretical model of the proposed CCS was derived. Based on the derived theoretical model, compensation methods to decouple the radial and axial motion measurements were proposed. In addition, an error analysis of the CCS was performed and a design rule was developed to guarantee the same accuracy in measuring both radial and axial motion measurements. Finally, a test rig and electronics for the proposed CCS were built and the effectiveness of the proposed CCS was verified through experiments and simulations. The developed CCS is expected not only to reduce the system complexity but also to afford a good balance between the radial and axial motion measurement accuracies.