The errors of the shaft's axial movement measuring in the single-coil-eddy-current-sensors-based system for the monitoring the state of radial thrust bearing of the NK-33 liquid rocket engine’s turbopump unit

Abstract

This article continues a series of publications devoted to the problems of early state diagnosis of the combined journal-and-thrust bearing of the turbo-pump unit of the liquid-propellant rocket engine NK-33, which is a critical node of the power plant under consideration. The proposed approach is based on the idea of replacing the standard induction sensors of the turbo-pump rotational speed currently used in turbo-pump unit by specially designed single-coil eddy current sensors with sensitive elements in the form of a segment of a linear conductor. The transducers are placed in the same mounting holes as the standard rotor’s speed sensors and their sensitive elements are oriented relative to the tooth of the measuring disc on the controlled shaft in such a way that the tip of the tooth remains in the sensitivity zone of both sensors during all possible movements of the shaft. The change in the axial position of the disk caused by the displacement of the rotor shaft in the radial thrust bearing during its destruction is determined on the basis of combined processing of the eddy current sensors’ output signals during the passage of the tooth under the sensors’ sensitive elements. The implementation of the standard rotor’s speed measuring function in the main and backup channels is ensured by fixing the moments of the tooth passage through the geometric centers of the sensitive elements of the first and second sensors in the cluster. The article is devoted to estimation of errors of the shaft's axial movement measuring in the channels of the system for monitoring the state of radial thrust bearing of the NK-33 liquid rocket engine’s turbopump unit. In particular, the random and systematic components of the basic error caused by the interference, the finite sampling frequency and the chosen method for calculating the desired shaft movements are given.