Nivus NFP, Инструкция по эксплуатации

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Instruction Manual
NIVUS Full Pipe
page 20 NFP - rev. 04 / 23.05.2018
After a certain period a second ultrasonic burst is sent into the medium (see Fig. 18-2). The
newly generated reflection signal is saved in the DSP too.
In various sections there are different flow velocities, where in case of full filled pipes and suf-
ficient calming sections the maximum velocity is in the centre of the pipe. Depending on me-
dium viscosity, flow velocity and wall roughness this velocity decreases approaching the pipe
wall (flow velocity profile, see Fig. 18-4).
The reflecting particles have moved away from the first measurement point by varying dis-
tances due to the flow velocity profile prevailing in the pipe. Hence, a distorted reflection pat-
tern results (see Fig. 18-3). At the same time slightly different reflections will emerge addi-
tionally resulting from the fact that some particles have been turning around and thus have
another shape of reflection; some particles are no longer within the measurement range and
others have now moved into the measurement range.
1 Pipe wall
2 Pipe sensor
E1…E7 Reflecting particles
1, 2, 3, 4, n Measurement window
Fig. 18-2 Situation at second signal detection
The DSP checks both the received reflection patterns for similarities using the cross correla-
tion method. All existing signal differences are rejected so that two similar but temporarily off-
set signal patterns are left for velocity evaluation.
Depending on the inner pipe diameter set an overlay consisting of up to 16 measurement
wind
ows of different lengths will be added. Then, in each measurement window the lag Δt of
the signal pattern is investigated (see Fig. 18-3).