The oscillating tube method uses the oscillating frequency of the glass U-shaped tube based on electromagnetic induction, that is, a magnet is fixed on the U-shaped glass measuring tube, and the oscillator makes it vibrate, and the vibration period of the glass tube will be measured by the vibration sensor. Each U-shaped glass tube has its characteristic frequency or vibrates according to its natural frequency. When the glass tube is filled with objects, its frequency will change, and the frequency of different substances will change differently, and its frequency is a function of the mass of the material filled in the tube. When the mass of the substance increases, its frequency decreases, that is, the vibration period T increases.

When measuring, select certain substances as standard substances, and after measuring the frequency, calculate the density value of the tested substance by the difference of the oscillation frequency between the tested substance and the standard substance.