Material interface level sensing

摘要

A system for measuring the level of the interface between gasoline and water in an underground gasoline storage vessel includes an electronics enclosure from which a transmission line probe extends for contact with the gasoline and water within the vessel. The transmission line probe carries a reflection target disposed at a fixed known position with respect to the electronics enclosure, and at a position normally to be covered by the gasoline. Electronics within the enclosure employ time-domain reflectometry techniques to determine the position or level of the air/liquid surface of the gasoline, and to obtain an apparent position reflection measurement from the target disposed within the gasoline. Since the actual distance from the electronics to the reflection target, as well as from the target to the bottom of the vessel, are predetermined and known, and the level of the air/gasoline interface has been determined, the distance between the air/gasoline interface and the target is determinable, and a compensation factor related to the dielectric constant of the gasoline can be determined. Time-domain reflectometry is employed in conjunction with this compensation factor to determine the true level of the gasoline/water interface beneath the reflection target.