Oscillating U-tube

The oscillating U-tube is a technique to determine the density of liquids and gases based on an electronic measurement of the frequency of oscillation, from which the density value is calculated.

In modern digital density meters, Piezo elements are used to excite the U-tube whereby optical pickups determine the period of oscillation.

This period τ can be measured with high resolution and stands in simple relation to the density ρ of the sample in the oscillator: A and B are the respective instrument constants of each oscillator.

Modern instruments calculate and store the constants A and B after the two calibration measurements, which are mostly performed with air and water.

In 1967 the company Anton Paar GmbH presented the first digital density meter for liquids and gases employing the oscillating U-tube principle at ACHEMA.