Importance

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Abstract

A storage installation which is capable of storing a variety of free-flowing materials, both conductive and non-conductive, includes a level sensing device disposed preferably vertically therein. The device has a plurality of level sensor and sensor circuit pairs disposed vertically within a non-electrically conducting tube which is hermetically sealed from contact with the stored material. The level sensors comprise plural sensing capacitors, each having cylindrical upper plates and grounded lower plates. Electrostatic force lines from the sensing capacitors penetrate walls of the sealed tube, and are differentially interfered with by the presence or absence of material to be sensed. Such interference affects the dielectric constant of the respective sensing capacitor, which can in turn be detected by a relatively small corresponding circuit housed directly in the tube. DC signals from the respective circuits are brought out of the tube to drive a level indicator display. Elimination of metal or electric contact with the material being sensed makes the device safe for use with combustible materials such as gasoline. Use of a DC signal output instead of a frequency dependent signal eliminates the need for adjustments during field installation to compensate for stray capacitance or inductance.

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First Claim