Rice Lake Weigh Modules/Mount Assemblies - Manual (Page 6)

SYSTEM DESIGN
1-4
Bulk Material Weighing Systems
F. Figure 1-10 illustrates a loss in weight system. This is used
where a process needs a batch of material (not more than the
capacity of the weigh hopper), but that material needs to be
fed to the process at a controlled rate.
The process starts by filling the hopper with at least enough
material for the upcoming process. The fill is then stopped
and the discharge commences. The rate at which the dis-
charge takes place is controlled by monitoring the “loss in
weight” of the hopper and then modulating the discharge
rates to maintain the desired flow rate. The discharge may be
ended at the completion of the process step, or when a specific
amount of material has been discharged.
Advantages of this system are:
•
Gives the ability to supply material at a constant rate
Disadvantages of this system are:
•
Complex controls and mechanical arrangement
• Higher cost than pulse discharge systems.
D. This arrangement is similar to Example C, however, a lower
surge hopper has been added to speed up the discharge cycle.
This system, shown in Figure 1-8, is typically used in multi-
draft grain loadout systems where multiple drafts are re-
quired to fill a rail car or barge. The weight of each draft can
be accumulated and the target weight of the final draft
adjusted to achieve the desired car net load.
Advantages of this system are:
• Weigh hopper isolated from feed conveyor.
• Surge hopper serves as a buffer to smooth out demand.
• 2-speed fill is possible.
• Faster fill, discharge, and throughput possible.
Disadvantages of this system are:
•
Higher overall height.
• Higher cost.
• More complex controls and mechanical arrangement.
The systems described up to this point deliver a single material in
pulses rather than from a continuous flow. They may be used for
in-plant process weighing or custody transfer. Figures 1-9 and 1-
10, described below, provide a continuous material flow and are
more often used for process weighing.
E. Figure 1-9 illustrates a single storage silo with two weigh
hoppers suspended underneath. This arrangement can be
used to provide material continuously to a process. As one
hopper is emptying, the other can be filling If the system is
sized correctly, there is no interruption to the material flow
on the discharge belt.
Advantages of this system are:
•
Continuous material flow.
• High throughput possible.
Disadvantages of this system are:
•
Higher overall height.
• Higher cost than pulse discharge systems.
• More complex controls and mechanical arrangement.
Figure 1-9
Figure 1-10
Figure 1-8