VEGA WEIGHTRAC 31 Foundation Fieldbus - Manual (Page 50)

50
7 Setup with PACTware
WEIGHTRAC 31 • Foundation Fieldbus
42375-EN-131120
It is therefore important to detect the weight of the conveyed material
correctly. This means that you have to use a precise, possibly also
calibrated, scale.
Make sure that no material is lost from the belt or the transport and
that no foreign material is added. If you carry out the measurement
with a truck, make sure that you have comparable measuring condi-
tions (always measure with or without driver, use the same vehicle or
compensate for differences, make sure there is no residue buildup on
the loading platform of the vehicle, etc.).
Make sure that the density of the material during the linearization cor-
responds to the original material measured later on.
Fig. 33: Add adjustment points
Due to the measuring principle, there is no linear relationship between
pulse rate and level. Hence, this adjustment (i.e. linearisation) must in
any case be carried out.
For very precise measuring results, you should carry out this adjust-
ment with different filling heights (flow rates) on the conveyor belt. The
bigger the difference in flow rates, the more precise the linearization.
The way you measure the total quantity of the conveyed material
depends on the options you have on site.
You can collect the total quantity of conveyed material on a truck and
determine the weight with a truck scale. But you can also weigh the
material before the measurement and keep it ready for the lineariza-
tion. Another possibility would be to transfer the conveyed material to
a container sitting on load cells.
You can carry out the linearization with two different principles:
•
Dynamically - with running conveyor belt
•
Statically - with stationary conveyor belt
Dynamic linearization
During dynamic linearization you simulate the actual operation of
the conveyor belt with the known material quantity. For a dynamic
linearization you need at least 20 % of the max. process value. If the
measuring range is e.g. 0 … 200 t, then at least 40 t of material should
be available for linearization.