FMCW radar in oil-filled waveguides for range detection in hydraulic cylinders

Highly precise distance measurement sensors are essential in the field of industrial automation. In particular hydraulic cylinder applications require an accurate detection of the piston position by reason of controlling and monitoring. Currently used external as well as integrated solutions are limited by many factors. Using low-cost and precise radar sensors is a highly promising approach for these applications. In this paper a K-band FMCW radar sensor is used to detect the position of the piston in a hydraulic cylinder with a guided propagation of the radar signal. Requirements for this new approach are described and verified under real measurement conditions. The achieved accuracy for a 1 m hydraulic cylinder is well below 200 μm at a measurement repetition rate of 2 kHz.