Blade vibration has been recognized as one major cause of failure in turbo-machinery which has directed enormous efforts towards developing reliable techniques for its measurement. Available blade vibration measurement techniques can be classified into two broad categories, namely: (1) the direct approach, such as using strain gages bonded at the blade, and optical/laser methods, to monitor the blade motion directly at one or more points on the blade span, and (2) the indirect approach, by extracting some blade vibration information from the main rotor lateral vibration, casing/bearing cap vibration, pressure fluctuations, performance monitoring and thermal changes. Recently, an indirect method, monitoring the torsional vibration of the main rotor, has been under theoretical and experimental studies. Based on previous studies, direct and indirect techniques are described in this survey paper. The advantages and drawbacks of different blade vibration measurement methods are summarized towards reaching an assessment, identification of the existing problems and recommendations for future work.
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