Measuring physical properties such as density or sound velocity is a tried and tested method of monitoring the concentration of liquids and is used in a wide range of processes.

By combining density and sound velocity measurements, it is even possible to determine the concentration of three-component mixtures.
Classic laboratory methods for determining density such as pycnometers or hydrometers cannot be used for continuous measurement in process because they are not suited to measuring flowing sample. The so-called oscillating U-tube method, developed in 1967 by Anton Paar GmbH, is suitable for both flowing and non-flowing liquids, and is also much more accurate than the other methods.
The liquid flows through a U-shaped tube which is electromagnetically excited to oscillate continuously at its natural frequency. The frequency is directly dependent on the density of the liquid in the U-tube. The period of oscillation is measured with high precision and sent to the microprocessor in the analysis unit together with the temperature, so that the density or concentration can be determined.

ENQUIRY No 11

Anton Paar is based in Graz, Austria. www.anton-paar.com