Novel Combination 3DOF Radial/Axial Eddy-Current Position Sensor

A novel noncontact three-degree-of-freedom radial/axial eddy-current position sensor for applications in active magnetic bearings (AMBs) is developed. The sensor meets the most demanding industrial requirements, including ability to work in dusty environments and in many working fluids, low sensitivity to temperature changes, as well as external electrical and magnetic fields, excellent linearity over a large displacement range, large intrinsic gain, easy integration into a machine, robustness to variations in parameters of the external wiring, simplicity of the signal processing electronics, and large frequency bandwidth. The sensor is inexpensive in volume and well suited for high-volume production. It has been successfully integrated into a commercial 175-kW air compressor, which was spun to the full operation speed of 50 kRPM. Operation with a 4-m twisted-pair sensor cable has been demonstrated and using much longer (tens of meters) cables would be possible with design modifications. Even though the sensor was developed for AMBs, it can find other uses in rotating machinery and beyond.