Simultaneous Measurement for Blade Tip Clearance and Vibration Based on Capacitive Probe

Rotating blade is a critical but fragile component in the aero-engine. Due to harsh working conditions like high rotation speed, and heavy load, rotating blades are prone to failures, which endanger the operation safety of turbomachinery; thus, it is important to detect incipient failure in time by monitoring the blade tip vibration. In addition to blade vibration, the clearance between the rotating blade tip and the casing is another key indicator that reflects the working performance and operation safety of the aero-engine. At present, tip vibration and clearance measurement are implemented by two separate measurement systems, i.e., blade tip timing (BTT) and blade tip clearance (BTC) systems. Two separate systems greatly increase the cost and risk of rotating blade condition monitoring and make it prohibitive to install them in aero-engine. Consequently, it is urgently needed to simplify the measurement system. In this paper, we provide new insights into the potential for capacitive probe-based measurement system's use as a simultaneous measurement for BTC and BTT. Specifically, we use dual capacitive probes to record the original voltage waveforms. Subsequently, from the voltage waveforms, we derived the BTT and BTC signal based on a constant proportion threshold and a calibration, separately. Experiment results demonstrated the derived BTT and BTC signals contain the tip vibration and tip clearance information, and show the feasibility of simultaneous measurement for tip clearance and vibration signals based on capacitive probes.