Uncertainty analysis of vibration measurements of tools inside fluids by laser Doppler techniques

The study of the vibration of bodies immerged in fluids is very interesting for both industrial and scientific research. Many applications are possible in the maritime field (vibrations of propeller, submerged mechanical bodies), in the turbine field (blades in contact with water or overheated steam), in some industrial processes, for example monitoring of the tools vibrations with lubricants and refrigerant film, mechanical couplings in contact with lubricants. Usually the classic instrumentation used for vibration measurement (accelerometers) could not be employed because of its intrusivity (small vibration objects) or because bodies are in motion (machine tools for processing with removal of shaving). The measurement "without contact," based on the employment, for example, of proximity sensors to measure displacements (and therefore acceleration) of the objects under examination is possible. Often, their accuracy is not sufficient and their signal could not be derived in time to calculate the acceleration from the measurement of displacement. Furthermore the presence of fluids is not suitable for some of these instruments (for example capacitive, heddy current or optic systems). In this work a new technique based on the laser Doppler interferometer is examined. Some commercial interferometers are studied. Optical test benches have been set up to examine the behaviour of these instruments when the measurement bundle laser goes through a fluid.