A high sensitivity inductive sensor for blade tip clearance measurement

A multiplexed inductive sensor consisting of multiple mini-sized planar spiral coils for detecting multiple tip clearances of rotor blades is presented. The sensor measures the tip clearances by monitoring the inductance changes of planar spiral coils caused by the passage of the rotor blades. A resonance frequency division multiplexing technique and parallel LC resonance measurement were applied to the multiple sensor coils, making it feasible to measure multiple tip clearances using only one set of measurement electronics with high sensitivity and resolution. The results from tests conducted on a bench-top test rig have demonstrated that the sensor is capable of simultaneously measuring multiple tip clearances from 0 to 5 mm with a 10 mu m resolution at a high rotary speed up to 80 000 RPM. With its high resolution, high sensitivity and capability of monitoring a large number of tip clearances simultaneously, this sensor can potentially be used for advanced active tip clearance control in turbine machinery.