Ultrasonic measurement of density of liquids flowing in tubes

The measurement method employs a double element transducer (DET) which consists of a piezoelectric ceramic transmitter and a large aperture PVDF membrane receiver separated by a polymethyl-methacrylate (PMMA) buffer rod. Between the receiver and the liquid there is a reference PMMA rod. The density is obtained from the reflection coefficient for the interface of the reference rod and the liquid, and the transit time between this interface and a reflector placed at the opposite wall of the tube. The DET is calibrated once to account for temperature effects. The calibration is incorporated in the signal processing such that in the actual measurement, the temperature of the system is taken into account. The error of measurements performed with this method in water, castor oil and alcohol, at different temperatures, compared with data in the literature or obtained by a pycnometer is less than 1.5%.