Flexim FLUXUS F704**-A2 Series, Руководство пользователя

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FLUXUS F70x 3 General Principles
14 UMFLUXUS_F7V4-6-2EN, 2017-10-01
3.2.3 Measurement of the Flow Velocity in the NoiseTrek Mode
When media with a high proportion of gas bubbles or solid particles are measured, the attenuation of the ultrasonic signal
increases and can inhibit the propagation of the signal in the medium. A measurement in the TransitTime mode is no lon-
ger possible.
The NoiseTrek mode uses the presence of gas bubbles and solid particles in the medium. The measurement setup used
in the TransitTime mode does not need to be changed. Ultrasonic signals are sent into the medium at short intervals, re-
flected by the gas bubbles or the solids particles and again received by the transducer. The transit time difference be-
tween two consecutive measuring signals that are reflected by the same particle is determined. The transit time difference
is proportional to the distance covered by the particle in the time between the two measuring signals and therefore to the
velocity at which the particle moves through the pipe (see Fig. 3.5).
The average value of all measured velocities of gas bubbles and/or particles corresponds to the flow velocity of the medi-
um:
v = k
Re
· k
a
·
with
Depending on the signal attenuation, the error of measurement in the NoiseTrek mode can be greater than in the Transit-
Time mode.
3.2.4 HybridTrek Mode
The HybridTrek mode combines the TransitTime mode and the NoiseTrek mode. During a measurement in the Hy-
bridTrek mode, the transmitter automatically toggles between the TransitTime mode and the NoiseTrek mode depending
on the gaseous or solid content.
v – flow velocity of the medium
k
Re
– fluid mechanics correction factor
k
a
– acoustic calibration factor
∆ t – transit time difference of the measuring signals
t
s
– time interval between the measuring signals
Fig. 3.5: Measurement of the flow velocity in the NoiseTrek mode

t
2 t
S

------------
gas bubble or
solids particle at t
gas bubble or
solids particle at t+t
s
transducer
signal 1
flow direction
of the medium
signal 2