The Importance of Accurate Weighing in Tumba Scales

"Tumba" is the general term used to describe a containment container whose design is influenced by the physical properties of the materials it is intended to hold. Such weighing devices are typically installed where the weight of "free flowing" materials in the hopper is to be determined. These scales typically weigh the types of materials that are not readily available on open, flat surfaces and should be limited in a container when weight is determined to avoid any loss of material. Companies that manufacture or process materials such as stone aggregates, coal, metal ores, scrap or recycled materials, liquid or granular chemical products; and agricultural grains are some examples of the various processes in which such flakes can be found. The capacities of these scales vary greatly and can range from under 50 kg to thousands of kilograms.

SELECTION OF A SUITABLE TUMBA SCALE
The considerations when choosing a hopper scale for a particular use are pretty much the same as for other weighing devices. The material being weighed, typical draft size, accuracy classification, resolution of the balance, and the ability to interface with the relevant equipment are some of the features to consider when deciding on a suitable instrument.

MEASUREMENT CAPACITY
A key feature to consider when choosing a hopper scale is the rated capacity of the scale needed for a particular application. Setting parameters for this feature should be relatively easy. The capacity will depend on the initial "dead load" value (the weight of the structural members to support the applied loads) as well as the maximum load expected to be weighed on the instrument. Manufacturers will typically design a scale with a capacity to include an expanded weighing capacity beyond the expected maximum load. This additional capability is designed to prevent potential damage from overloading and to withstand the effects of "shock" loading.

TUMBA HOPPER CAPACITY
In addition to the capacity of the tumba scale, it is necessary to determine an appropriate value for the weighing chamber. The suitability of the weighbridge is somewhat of a practical matter, as it often depends on the monetary value of the item being weighed. The material value of a weighbridge should be taken into account when recognizing that human-made devices will inherently contain some errors, and when these weighing devices are allowed to allow some deviation from the actual weight value when specifying a weight.
For example, on a 0.5 kg scale, a weighing error in a hopper would represent a financial loss of 5.00 ₺ for a commodity priced at 10.00 ₺/kg. However, for a commodity priced at $0.10/kg, this error only represents a monetary value of $0.05. As illustrated here, a single hopper weighing variation can have a large impact on a process, so hopper size is an important consideration.