Cubemass DCI
Hauser
3
Function and system design
Measuring principle
The measuring principle is based on the controlled generation of Coriolis forces. These forces are always present
when both translational and rotational movements are superimposed.
F
C
= 2 ·
Δ
m (v ·
ω
)
F
C
= Coriolis force
Δ
m = moving mass
ω
= rotational velocity
v = radial velocity in rotating or oscillating system
The amplitude of the Coriolis force depends on the moving mass
Δ
m, its velocity v in the system, and thus on
the mass flow. Instead of a constant angular velocity
ω
, oscillation occurs.
This causes the measuring tube loop through which the fluid is flowing to oscillate. The Coriolis forces
produced at the measuring tube loop cause a phase shift in the oscillations of the tube loop (see illustration):
• If there is zero flow, i.e. when the fluid stands still, the oscillation measured at points A and B has the same
phase, and thus there is no phase difference (1).
• Mass flow causes deceleration of the oscillation at the inlet of the tube loop (2) and acceleration at the
outlet (3).
A0003383
The phase difference (A-B) increases with increasing mass flow. Electrodynamic sensors register the tube loop
oscillations at the inlet and outlet.
Compared to two-tube systems, other design solutions are required in single-tube systems to ensure system
balance. In the case of the CNGmass DCI, an internal reference mass is provided for this purpose.
The measuring principle operates independently of temperature, pressure, viscosity, conductivity and flow
profile.
Density measurement
The measuring tube is continuously excited at its resonance frequency. A change in the mass and thus the
density of the oscillating system (comprising the measuring tube loop and fluid) results in a corresponding,
automatic adjustment in the oscillation frequency. Resonance frequency is thus a function of fluid density. The
microprocessor utilizes this relationship to obtain a density signal.
Temperature measurement
The temperature of the measuring tube loop is determined in order to calculate the compensation factor due
to temperature effects.
This signal corresponds to the process temperature and is also available as an output.
1
2
3
A
B
A
B
A
B
