Speed Measurement Method for Moving Conductors Based on Motion-Induced Eddy Current

Speed measurement plays an important role in many measurement and control systems in the industry. A simple and efficient speed measurement method for smooth conductive specimens based on motion-induced eddy currents (MIECs) is studied in this article. The speed sensor consists of a magnet and a Hall element. When the conductor moves beneath the magnet, eddy currents are generated, which further generate a secondary magnetic field that is dependent on the moving speed of the conductor. The Hall element picks up this field to determine the relative speed between the conductor and the sensor. First of all, a 2-D analytical model for the induced eddy currents and corresponding magnetic fields has been proposed by solving Maxwell's equations using spatial Fourier transforms. Then, the change in current density and magnetic field with conductor speed is analyzed using both the analytical model and the finite element method. Speed-sensing experiments were conducted on a rotating conductive disk, the results showed good agreement with the proposed analytical model. Finally, specifications such as accuracy, repeatability, linearity, and resolution of the prototype sensor have been tested.