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

Proline Promass 80A, 83A

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.
The measuring tube, through which the medium flows, oscillates. The Coriolis forces produced at the
measuring tube cause a phase shift in the tube oscillations (see illustration):
• At zero flow, i.e. when the fluid is at a standstill, the oscillation registered at points A and B is in phase,
i.e. there is no phase difference (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.
Compared to two-tube systems, other constructive solutions are required for the system balance for single-tube
systems. For this purpose, Promass A has an internal reference mass.
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 measuring tube and fluid) results in a corresponding, automatic
adjustment in the oscillation frequency. Resonance frequency is thus a function of fluid density.
The microprocessor utilises this relationship to obtain a density signal.
Temperature measurement
The temperature of the measuring tube 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.
A
B
2
A
B
3
B
a0003383
3