Off-line synchronous resampling of vibration measurements

A lot of advanced signal processing and analysis methods are available for digitized vibration signals with a fixed sampling frequency. On the other hand, specialized hard- and firmware has been designed and commercialized to synchronize the sampling frequency during a measurement with a second but related event. A well known mechanical application is the extraction of “order-related” phenomena of engine vibrations, based on the measurement of the rotation speed of one of its components. This paper describes the background and use of well-established digital signal processing techniques like digital resampling and filtering to convert signals from one domain into another, using a known or measured relation between both domains (e.g. between the time domain and the engine cycle domain). It particularly illustrates how phenomena can hardly be analyzed or interpreted in one domain, but become clear and obvious in the other domain. Emphasis of the paper is on the application to vibration measurements rather than on, theoretical aspects of the digital signal processing techniques involved