Measurement of Rotor Clearance Using a Dual-electrode Electrostatic Sensor

Clearance monitoring of rotors is of 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. A novel technique is proposed in this paper for the noncontact measurement of the clearance of a metallic rotor through electret-assisted electrostatic sensing and correlation signal processing. A single charged electret marker is used as a tracer and attached to the surface of the rotor as a stable charge source for the electrostatic sensors. The clearance measurement is inferred from the rotational speed measured through autocorrelation and the transit time measured through cross-correlation. A geometric relationship between the electrode position and the rotor axis is established. A series of experimental tests were conducted in a temperature and humidity-controlled chamber to evaluate the impact of ambient conditions on the performance of the sensor. Experimental results suggest that, an increase in ambient temperature and relative humidity has a minimal impact on the correlation characteristics of signals. Within the speed range of 120 – 3000 rpm, this technique enables the measurement of the metallic rotor clearance across the range of 2 – 18 mm, with a relative error within ±6%.