Issue link: https://www.e-digitaleditions.com/i/507774
18 May 2015 Tablets & Capsules powders into a vessel mounted on load cells, which must detect the weight of that powder addition as well as the full weight of the vessel and the powder it already contains (called the full scale capacity). Because most high- capacity load cells and floor scales don't have enough speed or resolution to detect the weight of a small amount of powder relative to the much larger overall weight of the vessel and its contents, a GIW system's expected batching accuracy is typically ±0.5 percent of the full scale capacity. However, the LIW feeder can achieve batching accuracies of ±0.1 percent of the batch set-point. This is because the LIW feeder's operation depends on sensing only the weight of the ingredient being fed rather than the much larger weight of the vessel and all of its contents, and the LIW feeder's high-speed load cells provide very high resolution (typically one part in four million). The LIW feeder can also speed your batching operation. When a Both LIW feeders and GIW feed- ing systems can be used in batching applications, but they work in funda- mentally different ways. These differ- ences typically make the LIW feeder better suited for dispensing powder actives or other ingredients with high accuracy requirements. The LIW feeder is suspended from or rests on high-speed load cells and dispenses powder into a granulator, blender, or other process vessel at a rate based on sensing the feeder's loss in weight. The LIW feeder's weight- sensing device provides high-speed, high-resolution weight-loss measure- ments of the powder in the feeder hopper. An example of an LIW batching application with two LIW feeders simultaneously dispensing ingredients into a process vessel is shown in Figure A. The GIW feeding system includes one or more volumetric feeders above a process vessel that's suspended from high-capacity load cells or rests on a high-capacity floor scale. Each volumetric feeder sequentially dis- penses powder at a rate based on sensing the gain in weight of the entire vessel and its contents. In the GIW batching application shown in Figure B, two volumetric feeders sequentially dispense ingredients into the process vessel. Which feeder type is best for your batching application depends on sev- eral factors, including the total batch size, the number of ingredients in the batch, your desired batching time, each ingredient's flow characteristics, and your application's accuracy re - quirements. When the batch ingredi- ent is an active pharmaceutical in gre - dient, feeding accuracy can be a cri tical factor in determining whether the LIW or GIW batching method is best. Here's why: With a GIW feeding system, a volumetric feeder dispenses GIW system handles an application with multiple ingredients, multiple volumetric feeders (one per ingredi- ent) must dispense ingredients one at a time into the vessel, because the vessel is weighed for each ingredient. In contrast, multiple LIW feeders can all dispense their ingredients at the same time into the vessel, because each ingredient is weighed as it's dis- pensed. This significantly cuts the total batching time. Be aware, however, that using LIW feeders for all the powders in a multi- ingredient batch can be expensive. A cost-saving alternative is to select a batching system that in cludes both GIW and LIW equipment. The GIW system can handle the lower-cost ingredients that have lower accuracy requirements. The LIW feeders can dispense the more costly ingredients, such as actives, that have higher ac - curacy requirements or can dispense ingredients required in a large quan- tity, thus cutting the total batching time. —S.N. Comparing LIW batching with GIW batching Figure A LIW batching LIW feeders Process vessel Figure B GIW batching Volumetric feeders Process vessel suspended from load cells