Difference between revisions of "Filling Scales"

Containers are often filled by weight. These can include drums,  cylinders, tanks, pails, cartons, totes, and almost any other type of  box. While it may be more convenient to fill by volume, there are a  number of parameters that can affect the accuracy. Depending on the type  of material being filled, it may compact differently depending on the  temperature or the relative humidity. The particles may cling to each  other by static electricity. The filling force may push the material  together, or may allow it to incorporate air. The density of the  material may differ. Therefore, filling scales may  be needed to increase the level of accuracy obtained. The weight can be  independently determined by use of the scale, which will generally be  underneath the item being filled. Of course it is important to de-couple  the filling tube or hose from the container, so that it does not affect  the reading. It may also be useful to control the rate of filling. A  rapid feed rate may apply a downward force into the container, and onto  the scale, also causing errors. It is very useful for filling scales to include setpoints for control  purposes. Generally set by the operator, a setpoint may give a visual  and electrical signal that can be used to automatically turn off the  feeding device, which may be a pump, augur, conveyor or similar. A  second setpoint will often be set somewhat lower than the first, and may  be used to slow down the rate of feed. This will provide enhanced  accuracy. Scales used for this purpose should be quite rugged, to accommodate  the high forces that may be applied when the full container is removed  from the scale platform. Stainless steel load cells are the best choice  for this purpose. It is also convenient to use a scale with a low  platform height to provide easy access for loading and unloading.