Functional description
NivuFlow Stick - rev. 00 / 27.01.2020
Page 19
Functional description
19 Operating Ranges
NivuFlow Stick is a mobile flow measurement system. The instrument is designed mainly for
measurement in slight to heavily polluted aqueous liquids of various compositions.
It is used within the scope of discharge measurements in rivers, flumes and channels featur-
ing various shapes and dimensions.
An overview on connectable sensors can be found in Sect. “15.1 Connectable sensors”.
Note on the ultrasonic reflection principle
The measurement method for flow velocity detection 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).
20 Functional Principles
20.1 Flow velocity measurement 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. 20-1). 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. 20-1 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. 20-2).