Sensors for Measuring the Volume and the Angular Orientation of the Liquid Surfaces in Axially Symmetric Tanks at an Indeterminate Orientation of the Tanks in Space

The article discusses the need for highly accurate sensors to determine the volume and the angular orientation sensors of the liquid surfaces in fuel tanks of the upper stages of spacecrafts. Existing sensors of this type do not always meet the stringent accuracy and reliability requirements, especially under conditions of indeterminately orientated liquid surfaces. The principle of construction and design of such sensors for axially symmetric tanks (spherical, cylindrical, lenticular, etc.) is proposed, which can provide simultaneous measurements of the amount of liquid in the tank and the angular orientation of the liquid surface with high accuracy under the specified conditions. This sensor consists of one linear and several ring sensing elements immersed in the liquid and designed to sense the immersion depth and relay this information as a signal. The linear sensing element is installed along an axis passing through the tank center and the intake port, while the ring elements are installed in a plane perpendicular to this axis, separated from each other by a distance determined by a specific error. The operation of the linear and ring elements could either be thermoresistive or capacitive in nature. In the latter case, the sensing elements may take the form of resonant circuits consisting of one linear and several ring capacitors, to which inductors are connected. Algorithms have been developed for converting the resonant frequencies of at least two sensing elements from the group of linear and ring elements into the parameters of interest. After estimating the contribution of various factors such as the sensor design discreteness, the geometric spread of the tank and its sensing elements, and the accuracy of the individual sensing elements themselves, we found that the accuracy of the individual sensing elements was the primary factor limiting the accuracy of the sensors. When the error of these elements was reduced to 10⁻³, the corresponding errors in the measured angle and volume were no more than 2.2∙10⁻² and 3.2∙10⁻³, respectively. The proposed sensor can be used to measure the parameters of interest in objects characterized by an undetermined spatial orientation such as spacecrafts, and sea vessels during heeling.