Nivus NivuFlow 750, Инструкция по эксплуатации

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Functional description
NFM 750 - rev. 03 / 27.05.2020 page 27
Functional description
20 Operating Ranges
The NivuFlow Mobile 750 is a portable measurement system for flow measurement. The in-
strument is designed mainly for measurement in slight to heavily polluted aqueous liquids of
various compositions.
The system can be used in part filled and full flumes, channels and pipes featuring various
shapes and dimensions.
An overview on connectable sensors can be found in chapter “16.2 Connectable Sen-
sors/Devices”.
Note on the ultrasonic reflection principle
The measurement method is based on the ultrasound reflection principle.
Hence, it is indispensable for the system to work that there are particles in the water, which
are able to reflect the ultrasonic signal sent by the sensor (dirt particles, gas bubbles or
similar).
21 Functional Principles
21.1 Flow velocity measurement
21.1.1 Cross correlation
The piezo crystal has a slope to the flow direction and operates as a flow velocity sensor.
Here an ultrasonic burst with a defined angle is sent into the medium. All the particles in the
measurement path (air, dirt) reflect a small amount of the ultrasonic signal. The result is a
particular signal depending on shape and size of the particles.
Hence, the multitude of the reflected signals results in a reflection pattern (see Fig. 21-1). The
piezo crystal receives this pattern again, which then is converted into electric signals and will
be saved in a built-in digital signal processor (DSP).
Fig. 21-1 Situation at first signal detection
After a certain period a second ultrasonic burst is sent into the medium. The newly generated
reflection signal is saved in the DSP too.
In various flow levels there are different flow velocities (flow velocity profile).
Depending on the level, the reflecting particles’ movement away from the first measurement
point therefore varies. Hence, a distorted reflection pattern results (see Fig. 21-2).