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.