Investigation of a digital eddy current sensor

摘要

Measuring the position of a moving or rotating target is one of the basic tasks for position control applications. Especially in the area of magnetic bearings, this plays a crucial role for stable levitation. Hence, the demand on reliable and affordable position sensor systems is high. Thereby, the sensor should feature high dynamics, a high resolution and low noise. State of the art systems are typically very expensive and, therefore, influence the feasibility of industrial applications. In this paper the working principle of a digital eddy current position sensor is presented which uses the effect of injection locking in oscillators. Due to the digital nature of the pulse width modulated position output signal it is obvious to skip the conversion to an analog signal, by means of low pass filtering. Instead, the controller digital signal processor is used for a time-to-digital conversion of the signal. This has the advantage that the costs of an expensive time to digital converter can be saved. To investigate the behavior, the position sensor system was simulated using a coupled finite element and electronic circuit simulation. Furthermore, measurements on the sensor were conducted to verify the simulation results and to analyze the performance of the sensor. Finally, the sensor system was tested in a one-axis magnetic bearing system and the results are presented.