Proline Promass 84F, 84M
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
, the Promass sensor uses oscillation.
In the Promass F and M sensors, two parallel measuring tubes containing flowing fluid oscillate in antiphase,
acting like a tuning fork. The Coriolis forces produced at the measuring tubes cause a phase shift in the tube
oscillations (see illustration):
• At zero flow, in other words when the fluid is at a standstill, the two tubes oscillate in phase (1).
• Mass flow causes deceleration of the oscillation at the inlet of the tubes (2) and acceleration at the outlet (3).
a0003383
The phase difference (A-B) increases with increasing mass flow. Electrodynamic sensors register the tube
oscillations at the inlet and outlet.
System balance is ensured by the antiphase oscillation of the two measuring tubes. The measuring principle
operates independently of temperature, pressure, viscosity, conductivity and flow profile.
Density measurement
The measuring tubes are continuously excited at their resonance frequency. A change in the mass and thus the
density of the oscillating system (comprising measuring tubes and fluid) results in a corresponding, automatic
adjustment in the oscillation frequency. Resonance frequency is thus a function of fluid density. The micro-
processor utilises this relationship to obtain a density signal.
Temperature measurement
The temperature of the measuring tubes 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.
The temperature measurement cannot be used to generate data for invoicing in applications subject to legal
metrology controls.
1
2
3
A
B
A
B
A
B
