Ultrasonic measurement of density of liquids flowing in tubes

This paper presents the implementation of the relative reflection method for the ultrasonic measurement of the density of liquids, which may be flowing in pipelines, at different temperatures. This technique will be shown to be valid for large-diameter tubes containing flowing liquids. It employs a double-element transducer, consisting of a piezoelectric ceramic transmitter and a large aperture PVDF membrane receiver, separated by a polymethylmethacrylate buffer rod. Between the receiver and the liquid is a PMMA reference rod. The density is obtained from the reflection coefficient of the reference rod-liquid interface and the transit time between this interface and a reflector placed in the opposite wall of the tube. The DET is calibrated once to account for temperature effects. The calibration is incorporated during signal processing, so that the actual density measurement is temperature compensated. In testing this method, a system was implemented and measurements of several liquids, stationary and flowing in a pipeline, were conducted. The error of measurements obtained by this method for distilled water, tap water, castor oil, and ethanol, when compared to data in the literature or obtained by a pycnometer, is less than 1.5%.