Hybrid computed order tracking

Vibration analysis is an integral part of modern condition monitoring and f ault diagnosis systems for rotating machinery. Orders (cycles per revolutio n) are used as a frequency base for this analysis, thus making speed-relate d vibrations easier to detect. Fundamental to the performance of such syste ms is the accuracy and reliability of the required synchronously sampled vi bration data. In this paper, the accuracy of three different synchronous sa mpling schemes are studied: a traditional hardware solution, computed order tracking and a hybrid of the two. Run-ups and run-downs are of particular interest in condition monitoring systems as they highlight many shaft defec ts. Also, because of the sometimes rapid shaft speed changes, this is just where the traditional approaches to producing synchronous sampling are pron e to producing erroneous results. The three methods are assessed on data pr oduced from a simulation of the rundown of a gas turbine shaft, typical to those found in the power industry. The use of this simulation allows the tr ue accuracy of the techniques to be accessed, and inadequacies of tradition al methods are clearly highlighted. The different sampling schemes rely on various interpolation algorithms. The accuracy and reliability of these alg orithms is fundamental to the performance of the different sampling schemes , and hence a survey of the state-of-the-art interpolation algorithms is pr esented. This ensures that the most appropriate algorithms are identified, and as a result the novel computed order tracking technique introduced in t his paper is shown to produce superior results. (C) 1999 Academic Press.