Calibration of X Band FMCW Radar Level Probe

In chemical industries, there are huge tanks filled with hazardous chemicals. These are present at extreme conditions of temperature and pressure. Measurement of the level in tanks is very important but difficult. Conventional methods to measure the level of the liquid in tank fails in such extreme conditions. It is because many times the conventional level sensors which are in contact with liquid gets corroded or have reaction with the chemical thereby contaminating the chemical and even damaging the level sensor. Hence non-contact level sensor finds its importance. A Level sensor developed at SAMEER, Mumbai in monostatic X band radar. Calibration plays very important role in removing offset and delays which are inherent in radars. In this paper, calibration method for this Frequency Modulated Continuous Wave (FMCW) based Radar level probe (RLP) is illustrated. The Calibration process involves setting parameters of front end transceiver, Radar experiments like ranging, analog and digital range resolution measurements etc. As calibration targets, flat plates and corner reflectors are used. The corrections are made accordingly after the testing which make the system response stable and linear. The calibration experiment was conducted on bench and in prototype water tank. Along with this, the mapping algorithm of liquid level to 4-20mA current is also shown.