Fluid level measurements using acoustical technique, which takes inhomogeneity of fluid into account

The ultrasonic level gages which use acoustic technique are widely used for measuring of fluid level in vessels. If the medium is inhomogeneous the measurement has a bias error. Moreover, it is impossible to evaluate the measurement error as the properties of the medium along the axis of the vessel are unknown. The proposed method is based on the theory of solving the Sturm-Liouville inverse problem for two spectra and is free from this error. The main point of the method is as follows. The motion of acoustic disturbance is described by the equation of acoustics for flat-layered medium which contains unknown vertical coordinate dependences of sound velocity and fluid density. As a result of measurement some properties of solution are obtained. Next unknown coefficients of this equation and finally required level can be found. The advantage of the approach proposed is that a variety of factors related to the characteristics of the medium in which the wave is propagated are taken into account automatically. By complicating the description of wave propagation, introducing additional characteristics of the medium into the equation of motion, and describing the process in more and more adequate form, accuracy of measurements can be increased. Numerical simulation of the level measurement process for the method based on the theory of solving the Sturm-Liouville inverse problem for two spectra is presented. The exponential profile of sound velocity is used for numerical simulation. The availability of analytical dependences makes it possible to calculate quite simply the initial data which are obtained in physical simulation as a measurement result. The efficiency of the proposed method, the algorithms of its realization and the possibility to use it in intelligent microprocessor instruments are shown.