Rice Lake Weigh Modules/Mount Assemblies - Manual (Page 63)

3-11
VESSEL ATTACHMENTS Flexure Mounting
As noted earlier, low-accuracy weigh systems may be partially
supported on flexures if the following conditions are met:
■ The vessel contents are self-leveling.
■ The vessel is symmetrical around a vertical line through the
content’s center of gravity.
These restrictions ensure that as the vessel fills, the center of
gravity of the contents rises along a vertical line whose location is
fixed relative to the support points. This ensures that each load cell
always sees the same proportion of the load.
The horizontal cylindrical tank illustrated in Figure 3-8 is mounted
on two flexures at one end and two load cells at the other.
It is very important that the vessel is level and the ends are identical
in shape. This is a lower-cost weighing system which will work
satisfactorily if low accuracy is acceptable.
Flexures may also be used with tension applications. Figure 3-9 is
an example of a circular vessel suspended from one load cell and two
flexures (or simply tension rods in this case).
Care must be taken to separate the flexures and load cells to
opposite sides or ends of the vessel. In Figure 3-9, for example, the
flexures could not be placed on one diagonal and the load cells on
the other.
If these vessels are to be calibrated electrically, then the geometry
of the vessel must be known accurately. This allows the percentage
of the load carried by the load cell(s) to be calculated. A practical
alternative is to calibrate with a known weight of liquid. It is not
practical to calibrate these vessels with test weights since they
could not be placed with any precision at the center of the vessel.
These arrangements should be avoided when the potential exists for
weight to be transferred from one support to another. This can be
caused by wind-loading, thermal expansion/contraction of pipes,
etc.
Low-Accuracy Systems: Partial Mounting on Flexures
Figure 3-9
Figure 3-8