Thursday, January 14, 2016

The Principle Behind the Coriolis Mass Flow Meter

ROTAMASS Coriolis mass flow meter
Coriolis mass flow meter
(courtesy of Yokogawa)
Have you ever witnessed this phenomenon? When a hose filled with water swings but it does not twist. But when the water flow is turned on and the water is forced through the swinging hose, the hose twists as a result of the changing angular velocity in the curved hose. That's the Coriolis effect in action.

Coriolis flowmeters are good for nearly all fluids, including high viscosity liquids, slurries and multi-phase media with a certain gas content.  Mass flow outputs from Coriolis meters have been know to be sensitive to gas bubbles in liquids,  but some designs have a special sensor that can tolerate a relatively high levels of gas in the process media.

The Yokogawa Rotamass operates on this principle. For practical exploitation of this principle it is sufficient for the two measuring tubes to perform oscillations on a small section of a circular path.  This is achieved by exciting the measuring tubes with an electromagnetic exciter in its first resonance frequency.

When no mass is flowing the 2 tubes oscillate symmetrically. But when a mass flows through the tubes, the tubes deform proportionally to the mass flow rate. This deformation is registered by two sensors, and forms the basis of the measuring result. A phase shift occurs between the first and the second sensor. The mass flow rate is derived from this phase difference. Should further the density of the media need to be determined, it is simply computed by evaluation of the oscillation frequency of the measuring tubes. With a single Coriolis device you can measure, simultaneously, mass flow density and temperature providing consistently top-notch measuring precision even amid changing media in process conditions.

See the video blow for a better understanding of how Coriolis mass flow meters operate.