Self-Calibrating Sensor for Measuring Density Through Stainless Steel Pipeline Wall

An ultrasonic instrument to measure the density of a liquid or slurry [1,2] through the stainless steel (SS) pipeline wall is described. By using multiple reflections of the ultrasound within the SS wall, the acoustic impedance (defined as the product of the density of the liquid and the velocity of sound in the liquid) is determined. Thus, the wall is part of the measurement system. The density is obtained by coupling the acoustic impedance measurement with a velocity of sound measurement. Since methods for measuring the time-of-flight (TOF) are well known, the research presented here will focus on the measurement of the acoustic impedance. The self-calibrating feature is very important because the measurement of the acoustic impedance is independent of changes in the pulser voltage. The objective is to develop an ultrasonic sensor that (1) can be attached permanently to a pipeline wall, possibly as a spool piece inserted into the line and (2) can clamp onto an existing pipeline wall and be movable to another location. The self-calibrating feature is very important because the signal strength is sensitive to the pressure on the clamp-on sensor. A sensor for immersion into a tank could also be developed. A U.S. Patent application has been filed.Copyright © 2002 by ASME