Clearance measurement of a metallic rotor using electrostatic sensors

Clearance monitoring of rotors is of vital importance for the safe operation of mechanical systems. It is essential for the system stability and early warning of faults to monitor the clearance of a rotor. This paper proposes a novel technique for the measurement of the clearance of a metallic rotor through electrostatic sensing and correlation signal processing. An electret marker is attached to the surface of the rotor as a stable charge source for the electrostatic sensors. The clearance measurement is inferred from the measured rotational speed through autocorrelation and the transit time through cross-correlation. A geometric relationship between the electrode position and the rotor axis is established. Experimental results suggest that, within the speed range of 120–3000 rpm, this technique is capable of achieving the clearance measurement of a metallic rotor with a relative error within ±8 % over the range of 2–16 mm.