Techniques for blade tip clearance measurements with capacitive probes

This article presents a proven but advantageous concept for blade tip clear ance evaluation in turbomachinery. The system is based on heavy duty probes and a high frequency (HF) and amplifying electronic unit followed by a sig nal processing unit. Measurements are taken under high temperature and othe r severe conditions such as ionization. Every single blade can be observed. The signals are digitally filtered and linearized in real time. The electr onic set-up is highly integrated. Miniaturized versions of the electronic u nits exist. The small and robust units can be used in turbo engines in flig ht. With several probes at different angles in one radial plane further inf ormation is available. Shaft eccentricity or blade oscillations can be calc ulated.