Function And System Design; Measuring Principle - Endress+Hauser Proline Promass 80E Technical Information

Proline Promass 80E, 83E

Measuring principle

Endress+Hauser

Function and system design

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.
= 2 · Δm (v · ω)
F
C
F = Coriolis force
C
Δm = moving mass
ω = rotational velocity
v = radial velocity in rotating or oscillating system
The amplitude of the Coriolis force depends on the moving mass Δm, 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 sensor, 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).
A
1
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.
Volume 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 density
value obtained in this way can be used in conjunction with the measured mass flow to calculate the volume
flow.
The temperature of the measuring tubes is also determined in order to calculate the compensation factor due
to temperature effects.
A
B
2
A
B
3
B
a0003385
3