Low volume ultrasonic resonator for liquid characterization under continuous flow conditions

A new ultrasonic resonator called MICRUS for measuring and characterizing liquid samples in continuous flow is presented. High accuracy and thermal stability are obtained by handling small liquid volumes passing through a heat exchanger before reaching the ultrasonic measurement chamber. The core measuring element consists of a resonant quartz flow-cell with LiNbO3piezoelectric discs attached face-to-face. The resonator is operated using pulsed excitation to provide rapid measurements. The software is implemented in LabView, giving a friendly and fully-automated interface well-suited for process monitoring. Different measurements for checking instrument performance (temperature stability, solute detection, measurement repeatability) are performed and a ±0.024 m s−1 uncertainty is obtained. Application examples requiring liquid measurement under continuous flow conditions are also presented. When monitoring processes taking place in containers and conduits with uncontrolled thermal conditions, results show that measurement stability can be kept under 0.1 m s−1 even when the sample temperature changes by more than 2 °C due to environmental variations.