It is discussed the need for non-intrusive monitoring of rotating blade vibration. The advantages over conventional techniques are outlined.

The vibration of a compressor blade has been investigated by strain gages, with particular attention to time evolution of the frequency spectra, at different operating speeds of the machine. These information are fundamental to the correct design of the non-intrusive measurement system.

The non-intrusive measurement technique has been presented, with special attention on uncertainty and resolution. The necessary hardware is discussed and the design of an optical sensor is presented.

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