Ultrasonic Gaging of Cryogenic Liquids

Abstract

Close examination reveals that liquid level devices measure either the position or height of a liquid surface above a fixed reference point, or the hydrostatic head or pressure developed by the liquid. A level measurement need not be expressed strictly in terms of inches or feet, nor in terms of the hydrostatic pressure developed. It may be conveniently interpreted in terms of volume or weight of liquid contained in a vessel provided its contour characteristic is known. The choice of units, by which the level information is to be expressed is governed by convenience and practicality. As in most process variables, liquid level can be measured directly or inferred. One of the more popular inferrential gages for measuring liquid level is the differential pressure gage frequently known as the Delta-P-System. This device is adequate for many simple applications but has difficiencies where a gage is required to provide information for a complex control system requiring extremely high accuracies and fast responses.