United States Patent Number: 5,231,883, August 3, 1993. 4 pages. Also available from the United States Patent and Trademark Office. Website: http://www.uspto.gov
NOTE: At the time of publication, the author William Durgin was not yet affiliated with Cal Poly.
An apparatus for defining the free surface of a moving column of a fluid in a vertical pipe to enhance the accuracy of measurements of transient rate of flow of the fluid using electromagnetic flowmeter is described. It provides a neutrally buoyant plug which stays in contact with the free surface of the column of the fluid at all times and thus defines the free surface of the fluid moving in the vertical pipe accurately and reduces the oscillations of the free surface of the fluid.