Coriolis mass flowmeter also capable of giving the density of the flowing fluid, it operates on the same principle as the spring and mass assembly as shown in the diagram below.

When the suspended mass is pulled down and released, it will move up and down, its motion both driven and limited by the spring, until the vibration is damped. The number of complete oscillations per unit time is referred to as the frequency of oscillation. As long as the mass of the object attached to the spring remains the same, whenever the object is pulled and released, the system settles to the same frequency until the movement is damped. This is referred to as the Natural frequency of the system.

If the amount of mass changes, the natural frequency of the system changes;

1. If the mass is increased, the natural frequency decreases; the weight and spring make fewer oscillations per unit of time.

2. If the mass is decreased, the natural frequency increases; the weight and spring make more oscillations per unit of time.

The frequency of oscillation is inversely proportional to the square root of the mass.

The exact relationship is expressed by the formula;

where;

f = the frequency

m = mass of the tube

K = constant representing the response of the spring

In the coriolis mass-flowmeter, the oscillating tubes correspond to the spring, and the mass of the tubes plus the mass of their contents corresponds to the mass of spring assembly. The drive coil that oscillates the flow tubes is energised periodically through a feedback circuit so that the tubes are always oscillating at their natural frequency.

Density is inversely proportional to the square of the frequency.

The equation is ;

where;

f = the frequency

m = mass of the tube

V = volume of the tube

K = constant representing the response of the spring

Since the volume and mass of the tubes and the spring constant do not change, the density of the fluid can be derived from the frequency of oscillation of the sensor which is mounted on the coriolis flow tubes .