Instruction Manual
NivuFlow 650
page 88
NF 650 - rev. 01 / 29.06.2020
32.1.13 v-determination Low Levels
Due to constructional and physical reasons the flow velocity sensors cannot measure the
flow velocity anymore below a certain minimum level. This minimum level is depending on the
mounting height of flow velocity sensors/paths.
Poor application conditions may push this level even higher. This level is referred to as
>h-crit<.
Fig. 32-7
v-determination low levels
The >v-determination low levels< menu facilitates the detection of temporary low flow volumes
(such as discharges at night, infiltration water or similar).
A requirement for this function is:
The application must be backwater-free.
Working principle:
As soon as the level falls significantly, from a certain point on it is not possible anymore to
measure the flow velocity.
The transmitter creates an internal table of v/h-readings at the point of the minimum level
(h-crit) on which a flow velocity still can be measured. The system here uses the latest
measurable flow velocity reading. The exponent of the channel shape set is considered auto-
matically to calculate this curve. As soon as no flow velocity can be recorded anymore, a level
however is measured, the system automatically computes an “appropriate“ flow velocity within
this value table.
•
>v-Determination Automatic<
If the box is checked (function active), the latest measured flow velocity value is used
as calculation value for low flow levels when >h-crit< is reached.
This calculated flow velocity value is used to compute the flow rate if the filling level
should continue sinking (below >h-crit<).
If the filling level is rising above >h-crit< and after that falls below again, the latest
measured valid flow velocity value is used for the next calculation of the flow rate.
If the box is not checked (function inactive) and the filling level falls below >h-crit< the
transmitter computes the flow rate by using the flow velocity value specified in >v-ma-
nual<.
If there are
very low flow levels
or backwater
or low medium quantities standing still at zero flow rates
expected within the channel, NIVUS GmbH recommend to deactivate the function by
