Position servo controller design and implementation using low cost eddy current sensor for single axis active magnetic bearing

Eddy-current sensors are the most commonly used position sensors in a magnetic bearing application. Most commercial eddy current sensor outputs analog voltage of 0-2 V or 0-5 V in their measurement range. Such eddy current sensors are quite expensive and are in the price range of $2500 (USD). This paper presents a design of a $20 (USD) low-cost eddy current sensor capable of resolving displacements of 7 micron which is suitable for high-speed position control in active magnetic bearings. A novel method of directly converting the time period of the square wave signal from the eddy current sensor output for digital servo position feedback is employed in this design. This paper presents a scheme to implement digital position servo control algorithm on Texas Instruments C2000 real-time microcontroller to control the position of magnetically levitated object by controlling the magnetic actuator's coil current. The magnetic actuators are electromagnetic coils that generate the magnetic force in the bearing.