Instantaneous Rotation Speed Measurement System Based on Variable Reluctance Sensors for Torsional Vibration Monitoring

In this paper, a system for the measurement of the instantaneous speed of rotating parts in turbines is proposed and modeled. The system is based on traditional and widely used variable reluctance sensors often mounted on-board for other purposes. By coupling this sensors with ad hoc rotating target (novel design) and front-end circuit, it is possible to extend the application of this sensor to accurate instantaneous angular speed monitoring, and to exploit it for torsional vibration monitoring or, in general, for the measurement of any other meaningful quantity related to the variation of the angular speed, useful for machine health monitoring and incipient fault diagnosis. The proposed rotating target produces a signal close to the pure sine wave, with the specific purpose of improving accuracy in torsional vibration monitoring. The complete system was modeled, also taking into account the effect of nonidealities in order to evaluate its performance. Experimental results confirm the satisfactory results obtained from simulations, and show the reduction of the magnitude of the higher order harmonics in the output signal spectrum ensuring improved performance for any torsional vibration monitoring assembly employing the proposed system.

I. Introduction

Machine condition monitoring can have a relevant impact on the performance of a plant or a machine and has attracted an increasing attention both from the industry and from the research community over the past decade. The goal of the machine health monitoring is to identify potential failure causes or failures at the early stage, such that timely adjustment and maintenance actions can be taken to reduce severe damage and expensive downtime. Condition-based maintenance based on different monitoring systems and techniques was proven to greatly reduce operating costs and improve reliability and availability of different machinery such as machine tools [1], automotive engines, and rotating machineries such as electric machines, compressors and turbines [2]. Health monitoring systems are based on the measurement of many different physical (or chemical) quantities [3] through suitable systems and sensors [2], [4]–[8]. In this context, the accurate measurement of the instantaneous angular speed (IAS) is particularly relevant for the condition monitoring of every rotating machines and in particular of turbines [9]–[11] because it allows the detection of many different fault conditions such as roller bearing [12] and rotor blades faults [13], and can be used in torsional vibration monitoring and analysis [14]–[20] systems.