Tubomachinery blade vibration amplitude measurement through tip timing with capacitance tip clearance probes

Turbomachinery blade vibrations can cause high cycle fatigue (HCF), which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has gone into investigating the ability of optical probes to achieve this. However, this paper looks at the potential for a dual use capacitance probe sensor to measure both tip timing and tip clearance. This paper provides new insights into the ability of a commercially available capacitance probe tip clearance measurement system for application as a non-intrusive turbomachinery blade tip timing measurement device. This is done by correlating capacitance probe tip timing results with simultaneously measured blade-mounted strain gauge vibration results and precise rotational speeds. Blade tip vibration amplitudes are measured using capacitance probes and compared to strain derived vibration levels. Thus the characterisation and quantification of the performance of the capacitance probe system when measuring blade vibration on a full-sized low-speed research compressor is analysed and reported.