A Novel Level Measurement Technique Using Three Capacitive Sensors for Liquids

The liquid level in a tank should be measured for most applications. In this paper, a new capacitive method is presented to detect the liquid level. Existing methods are generally approximations based on the large difference between the dielectric constants of the liquids and the air. The method proposed here eliminates the effect of air and gives the accurate reading of the liquid level in the tank. The main advantage of the method is that it can directly be applied to any kind of nonconductive liquid without calibration. The method is based on the measurements of capacitances of three parallel plate capacitive structures, which are designated as level, reference, and air sensors. It is mathematically proven that the method completely eliminates different factors, which affect the readings, such as air and temperature. The capacitance measurements are performed using a capacitance-to-digital converter integrated circuit, which can measure very small capacitances up to plusmn4 fF error. The result of a computer simulation, which demonstrates the performance and limitations of the proposed structure, is also provided.