Loss-in-Weight
Loss-in-weight (LIW), also known as differential feeding (Differenzialdosierung) in German, is a gravimetric feeding method in which the weight loss of a feeding system is measured continuously.
What are the key characteristics of loss-in-weight feeding?
To achieve this, the hopper and feeder are weighed together. As material is dispensed, the total weight decreases. The actual feed rate is determined and regulated based on this loss of weight over a specific period of time.
Loss-in-weight is primarily used for the continuous, precise feeding of bulk materials like powders, granules, pellets, or fibers.
How does loss-in-weight work?
At the beginning of the feeding process, a defined amount of material is contained in the hopper. While the feeder dispenses material, the weighing system continuously records the weight decrease. The control system compares the determined actual feed rate with the specified target value. In case of deviations, the feed rate is adjusted accordingly – by adjusting the speed of a screw, for example.
Once a certain fill level is reached, the hopper must be refilled. During this brief process, the feed rate cannot be determined by weight loss, since the total weight is increasing because of the inflowing material. In this phase, the feeder temporarily operates volumetrically, based on previously defined feeding parameters. Once refilling is complete, gravimetric control resumes.
What are the advantages of loss-in-weight?
Since loss-in-weight feeding continuously measures the actually discharged material, it can effectively account for variations in bulk density. This allows high feeding accuracy and a consistent material flow.
The process can be combined with various feeders. The choice of equipment depends primarily on bulk material properties and required feed rate capacity.