An Optimized Float for Reliable Radar Tank Level Measurement in Bypass Pipes

Abstract:
Tank Level Probing Radar (TLPR) systems are widely used in industrial process instrumentation for contactless level measurement of liquids in tanks. In difficult applications, like for example with agitators or other disturbing assemblies inside the tank, the radar distance measurement is sometimes performed inside a bypass, which is a liquid and gas tight communicating pipe mounted onto the side wall of the tank. In this paper, a new design of a metallic float, which is inserted into the bypass pipe as a well-defined radar target, floating on top of the liquid, is presented. The concept and the reflection properties of the proposed float have been evaluated and analyzed by means of electromagnetic field simulations. An optimized system for level measurement in a bypass pipe with an inner diameter of 38 mm has been implemented and evaluated by measurements with a Frequency Modulated Continuous Wave (FMCW) radar system working in the 5.7 to 6.7 GHz frequency range. High precision level measurements with an absolute error of smaller +/-2 mm were obtained by using the proposed float. Finally, it was found that the measurement results are largely independent of the slant and the varying eccentric position of the float inside the bypass pipe.