Speed Measurement of Rotating Hollow Shafts Using an Eddy Current Sensor

Rotating speed measurements of conductive hollow shafts using a new eddy current sensor are presented in this article. Two serially connected excitation coils are used, which are 180° geometrically shifted relative to each other. The pick-up coils have the same configuration as the excitation coils with a 90° geometrically shifted angle relative to the excitation coils. Parametric analyses of the speed sensor are performed using a novel developed analytical method. Detailed calculations of the sensor are presented using the 3-D time-stepping finite-element method. The performance of the eddy current speed sensor is measured up to 3000 r/min at different excitation frequencies. The rotating shafts are two hollow iron cylinders and three hollow aluminum cylinders with different shell thicknesses. The effects of the electrical conductivity and magnetic permeability of hollow shafts on the speed sensor performance are assessed. The measurement results are compared with the calculations for different shafts. The nonlinearity measured error is 0.15%.