This paper deals with BSSM, the noncontact blade vibration and tip clearance measurement system of MTU Aero Engines. Originally exclusively developed for vibration measurements on rotor blades of axial-flow compressors, BSSM has in recent years used capacitive probes instead of the former optical probes, for the reason that their signals can simultaneously be used also for blade tip clearance measurements. Signal digitalization in conjunction with intelligent trigger algorithms allow highly accurately timed triggering to be achieved despite the wide signal shape of these probes. The latest systems, therefore, include capacitive probes, suitable probe driver modules and a personal computer to process and analyze the signals. BSSM is continuously being improved and routinely used in rig and engine testing. This paper describes the current status of the system and addresses the following topics: motivation for the development of BSSM; probes and electronic hardware, probe positioning and calibration, analysis of resonant and asynchronous vibrations, and analysis of tip clearance related effects. The analysis methods are elucidated using comprehensive compressor test data.
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