A non-intrusive technique is presented for the detection of cavitation in a fluid filled pipe. This technique uses the coherence function between the signals from a pair of external sensors mounted on the pipe. In the non-cavitation conditions the phase structure between the signals is stable, giving high coherence. The presence of cavitation impairs the stability and produces a significant drop in coherence. The technique was examined using piezo accelerometers and PVDF coils as sensors. The latter output an electrical charge related to the pipe internal pressure pulsations by a linear transfer function. The detection of cavitation by the PVDF coil sensor has been found to produce superior results to that achieved by classical accelerometers.
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