Comparison of Eddy Current Sensors for Speed Measurement of Rotating Iron Shafts

This paper presents two eddy current sensors for rotating speed measurements. The sensors have one excitation coil and two antiserially connected saddle-shaped pickup coils. The small excitation coil is between two anitserially connected pickup coils in the first sensor. Two anitserially connected pickup coils are inside the second sensor's large excitation coil. The performance of eddy current speed sensors is evaluated and compared. The sensitivity of the speed sensors and susceptibility to the shaft material are calculated. A 2D analytical method and a 3D finite element method are used to model and analyze two eddy current speed sensors. The speed measurements are performed for a ±3000 rpm speed range at 500 Hz and 1000 Hz excitation frequencies. Two iron shafts with different material properties are selected for the measurements and analysis. An aluminum shell mounted on the solid iron shaft is used to increase sensitivity and decrease susceptibility to the shaft material. The optimization of eddy current speed sensors is presented to reduce the sensors' dimensions and evaluate the sensitivity and susceptibility to the shaft material. Despite its lower sensitivity, the first sensor has a lower susceptibility, between 1% and 2%, to the shaft material properties.