How to Properly Weigh Volume With the Right Scale

by : Christopher Carter

One of the most common tasks is to fill a number of containers with the same amount of material. These containers come in many shapes and sizes. They may be as simple as a cardboard box. Or they may be large cartons or even totes. For liquid or powdered materials, they may be pails or drums, or larger tanks. Liquefied gases may also be filled into tanks or cylinders.

In some circumstances it may be acceptable to fill the container by volume. Liquids may have a known specific gravity, so if the filling operation is being performed at a constant temperature, a consistent volume will give accurate filling results. For other applications, the accuracy may not be very important, so volume filling would be appropriate. But when good accuracy is required, filling by weight is usually the best choice.

There are a number of important characteristics of a good filling scale. Of course, the scale should give the same weight results independent of where the container is placed on the platform. It should also have good repeatability, so that the weight of every container will be accurate. Furthermore, it must be quite rugged. Filling scales are often damaged during the loading or unloading process. The best choice is for the scale to use stainless steel load cells, which will be much more abuse resistant then either aluminum or plated steel load cells.

Industrial filling will often have various levels of automation. The filling process may be accomplished with pumps and valves, conveyors or a variety of augurs or other filling devices. Setpoints may be programmed to output visual and audible signals to notify an operator when the proper target weight is reached. They may also output electrical signals that can be used with relays to control the filling device. To improve the level of accuracy, a somewhat lower target weight may be specified as the proper point to reduce the rate of feed to a trickle, and then use the final target weight for a final cutoff. In many situations, there may be more than one ingredient that is being dispensed into the container. Additional setpoint target weights may be used for each of these ingredients to produce a batch of material. For ease of use, the target weights may be stored in memory, by recipe. This recipe may be recalled from memory each time the same item is being formulated.

During the filling process, it may be desirable to print a label to place on the container. The filling scale may be able to send the information directly to a local label printer. Alternatively, this information may be sent to a computer system, which may then store the information in a spreadsheet or database, and also print the required label. Various types of communication standards may be used, such as RS-232, or the more modern Universal Serial Bus (USB. If a number of filling scales are in the same location, they may be networked with an RS-485 system. In some cases, it is required to be able to collect the data, and control the filling scale, from a remote location. An Ethernet connection on the scale will allow it to connect to the local area network. With the appropriate software systems, it will then be accessible from and web browser anywhere else.

Depending on the size of the containers that are being filled, the filling scale may be in the form of a bench scale, a cylinder scale, a platform scale or even a large floor scale. In all of these cases, it is best for the height of the scale to be minimized. This eases the loading and unloading process. Ramps should be available if drum carts are being used. The ramps may be equipped with anchor plates that allow them to be securely fastened to the factory floor. The same anchor plates can have a means of attaching to the legs of the scale, so the proper distance is maintained between the ramp and the scale.

The local digital indicator will be used by the operator to monitor the filling process. Large, graphics digits are very useful for ease of viewing in all types of factory environments. Units conversion allows the operator to read the weight in pounds or kilograms, or any other appropriate unit.