Yokogawa RotaMASS 3-Series - Manual (Page 19)

3. product description
3-1
IM 01R04B04-00E-E 8th edition March 01, 2011 -00 All Rights Reserved. Copyright © 2003, Rota Yokogawa
3. prOdUCT dESCrIpTION
3.1 The functional principle
The ROTAMASS instrument measures the mass flow with the help of the so-called Coriolis force. This force
occurs, when the medium being measured is flowing at velocity
ν through a tube that is rotating around an
axis perpendicular to the direction of flow at
angular velocity
ϖ.
When the medium moves away from the axis of rotation it must be accelerated to an
increasingly high peripheral velocity. The force required for this is called Coriolis force, after its discoverer.
The Coriolis force reduces the rotation. The opposite effect occurs, when the medium flows towards the axis
of rotation. Then the Coriolis force amplifies the rotation.
The formula for the Coriolis force is as follows:
Fc = - 2 m ( ϖ x ν )
The entire measurement tube is deformed slightly by the Coriolis forces, in the way shown. This deformation
is registered by movement sensors at points
S
1
and S
2
.
For practical exploitation of this physical principle, it is sufficient for the tube to perform sympathetic
oscillations on a small section of a circular path. This is achieved by exciting the measurement tube at point
E by means of an electromagnetic exciter.
The general construction of a Coriolis mass flowmeter looks as followed: