The development of a real-time fibre-optic shaft monitor using cross-correlation techniques

Everington, M. L. (2005) The development of a real-time fibre-optic shaft monitor using cross-correlation techniques. (PhD thesis), Kingston University, uk.bl.ethos.422002.

Abstract

A review of non-contact rotation measurement techniques has been undertaken. A non-contact sensor utilising optical fibres for the measurement of angular frequency and torsional strain in rotating shafts has been devised and tested. Initially a system was developed capable of measuring angular frequency over a range from 5 Hz to 1000 Hz to a resolution of 1Hz by monitoring variations in the intensity of the reflected light produced by the surface profile of the rotating shaft. Signal processing techniques such as windowing and auto-correlation were investigated in detail and proved beneficial in the reduction of noise thus enhancing the visibility of the peaks in the Fast Fourier Transform (FFT) spectrum. It was found that the best results were obtained using a Hamming window. In order to identify automatically the peak in the Fourier spectrum representing the rotation rate an algorithm was devised that enabled this to be determined when the peak containing the greatest energy was not necessarily that with the lowest frequency. The addition of a second identical channel enabling data to be collected at a different point along the axis of the shaft allowed the two signals to be cross-correlated and hence changes in the relative phase of the two points deduced. A digital cross-correlation technique was implemented on a PC. From this information torques up to 0.12 Nm have been measured, with a system resolution of 0.02 Nm and a response time of 1.5 seconds.

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