Optimization of electrostatic sensors for rotational speed measurement

Previous studies have proven that it is feasible and reliable to apply the electrostatic sensing technique to the speed monitoring of rotating machinery. The geometric shape, size, spatial position and spacing of the electrodes have significant influence on the performance of electrostatic sensors. This paper presents a scheme for the electrode optimization of electrostatic sensors. A mathematical model is established to determine the charge density distribution on the electrode surface based on the principle of electrostatic induction. Through mathematical modeling and numerical simulation, the spatial sensitivity and filtering characteristics of the electrostatic sensors are analyzed, then the optimal range of each electrode parameter is obtained. In order to assess the performance of sensors in speed measurement, an optimized sensor with double strip-shaped electrodes, is used to measure the rotational speed of a metallic shaft with an electrostatic marker attached. Experimental results show that, the rangeability of sensors is improved significantly. The system is capable of measuring the rotational speed as low as 30 RPM (revolution per minute) and achieving repeatable speed measurement over the range of 30 to 3000 RPM with a maximum error of ±4.5% and repeatability better than 1.9%.