The NASA Marshall Space Flight Center has developed a system for detecting the level of a liquid in a tank. Various methods have been proposed for determining liquid levels. It is known that a liquid level can be determined by positioning a capacitor inside the tank with either air or the liquid serving as a dielectric for the capacitor, depending on the level of the liquid in the tank. There must be a connection from the capacitor to a measuring circuit. Preferably, a coaxial cable is used to shield against any outside disturbance. However, the coaxial cable itself has some capacitance between its central conductor and the metallic shield. When the capacitance to be measured is very low and the coaxial cable is long, the inherent capacitance of the cable prevents an accurate measurement of the capacitance of the capacitor in the tank.

Benefits

Potential Commercial Uses

The Technology

A system for detecting the level of a liquid in a tank wherein a capacitor positioned in the tank has spaced plates that are positioned such that the dielectric between the plates will be either air or the liquid, depending on the depth of the liquid in the tank. An oscillator supplies a sine wave current to the capacitor and a coaxial cable connects the capacitor to a measuring circuit outside the tank. If the cable is very long or the capacitance to be measured is low, the capacitance inherent in the coaxial cable will prevent an accurate reading. To avoid this problem, an inductor is connected across the cable to form with the capacitance of the cable a parallel resonant circuit. The impedance of the parallel resonant circuit is infinite, so that attenuation of the measurement signal by the stray cable capacitance is avoided.

Patent Number

6,227,046

Contact for Licensing Information

If your company is interested in commercializing the System for Measuring Capacitance or if you need additional information, please reference case no. MFS-31195-1 and contact:

Technology Transfer Department
Patent Licensing Information
Mail Code CD30
Marshall Space Flight Center
Email: sammy.nabors@msfc.nasa.gov