Numerical Model of the Capacitive Probe's Capacitance for Measuring the External Loads Transmitted by the Bearing's Rolling Elements of Rotating Machines

Abstract

The bearings of rotating machines are comprised of rolling elements arranged between two coaxial rings. Rolling elements transfer the external load from one raceway to the other. This load's distribution on the rolling elements is uneven and depends on the internal geometry of the bearing and on the amplitude of the external load. In order to measure the transferred charge by a rolling element, a capacitive probe is inserted into the fixed ring of the bearing. This forms with the raceway a capacitor with variable gap that depends on the transmitted load by the rolling element. A numerical model of this capacitor's capacitance as a function of transmitted load by the rolling element has been established. This numerical model shows that there is a linear relation between the capacitance of the probe and the transmitted load by the rolling element. An experimental prototype has been established in order to precisely measure the probe's capacitance; the numerical model facilitates the access to the load's value. By placing a capacitive probe in front of each rolling element, the load transmitted by each rolling element can be measured. Therefore, the reconstruction of the shaft's external load on the rotary machine's bearing can be easily done.