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The feeder is located above a blender, granulator, reac- tor, or other process vessel and is suspended from a frame with three load cells to handle the large batch size. The load cells are connected to the feeder's controller. The controller is programmed to control the feeder to meter the powder at a high-speed (or bulk) flow rate into the vessel below it until the controller determines that the dispensed powder is within 90 percent of the powder's batch set-point. Then the controller automatically slows the feeder to a trickle (or dribble) rate to ensure that the feeder accurately delivers the desired batch weight. Two LIW feeders dispensing two powders into one vessel. In this batching application, two LIW feeders— one large and one small—each dispense a powder into a process vessel, as shown in Figure 2b. In this process, the final dosage form includes a large quantity of active, which is supplied in inter- mediate bulk containers. The large LIW feeder is suspended from a frame with three load cells and located below a discharger, which provides fully contained discharge through an air- tight connection into the feeder's hopper. The small LIW feeder receives a minor ingredient sup- plied in small bags; because this feeder handles less weight than the large LIW feeder, it rests on a platform scale with one load cell. Each small bag of powder is manually emptied into the small LIW feeder's hopper. Both feeders are connected to a controller that auto- matically controls the feeder speed at fast and trickle feed rates to accurately meet both ingredients' batch set- points. The LIW feeders allow simultaneous batching of both ingredients, reducing the overall batch cycle time. The feeders are also mounted on casters that roll on tracks, allowing the feeders to be rolled in and out of place as needed for cleaning. More about the LIW feeder's weighing system To provide the feeding control and performance required for accurate batching, the LIW feeder's con- troller must receive accurate high-speed measurements of powder weight changes from the load cells. This weigh- ing system (that is, the load cells and controller) must also filter out measurement errors caused by plant vibra- tions, non-uniform powder flow, or bulk density varia- tions and remain stable despite changes in the tempera- ture of the ambient air or powder. The higher the resolution of the load cell weight measurements and the faster the measurements are taken, the better the informa- tion going to the controller and the better its control and vibration-filtering algorithms will work. LIW feeders typically use analog strain gauge or digital load cells based on advanced weighing technologies. Work with your LIW feeder supplier to choose load cells that provide the speed, resolution, vibration-filtering capability, and stability your application requires. [Editor's note: For detailed information on load cells for LIW feed- ing and batching applications, contact the author.] LIW feeder options Your LIW feeder's components can be fabricated of various materials to suit your pharmaceutical or high- value powder. The components can also be designed to safely contain your powder while simplifying inspection, cleaning, and changeovers. Which components are best suited to your LIW feeder will depend on your powder's characteristics. For example, equipping the feeding device's outlet with a split butterfly valve (which combines active and passive components to provide maximum containment) will ensure that your powder is completely contained when the feeder is moved away from the process vessel after batching is completed. You can also select a feeder (and the hopper or receiver that discharges powder to it) with a retractable wash- or clean-in-place (WIP or CIP) spray system that eliminates many labor-intensive steps, thus ensuring fast changeovers and minimizing contami- nation between runs while protecting workers. The spray system also can pre-wet the feeder's interior before it's opened, thus wetting the dust and preventing it from becoming an airborne hazard to workers. Even a feeder equipped with a WIP/CIP system will still need to be dis- assembled for inspection from time to time, so look for feeding devices that give you quick, easy access. Consult your LIW feeder supplier for advice on select- ing the components that suit your powder's characteristics and containment requirements, as well as your expected inspection, cleaning, and changeover frequencies. Maximizing your LIW feeder investment Using a LIW feeder to accurately weigh and deliver pharmaceutical and other high-value powders to a process without manual intervention can provide several advantages. These include achieving better product qual- ity, reducing manufacturing costs, and obtaining maxi- mum yields. The feeder supplier can help you not only design the feeder to accurately and safely handle your tough powder, but help you combine the feeder and upstream and downstream equipment into a system that reduces your operating costs while maximizing your process efficiency and product quality. T&C Sharon Nowak is global business development manager at Coperion K-Tron Pitman, 590 Woodbury Glassboro Road, S e w e l l , N J 0 8 0 8 0 . Te l . 8 5 6 2 5 6 3 1 1 9 . We b si te : www.coperionktron.com. She holds a BS in chemical engi- neering from Rutgers University, New Brunswick, NJ, and has 24 years' experience in developing process equipment for the pharmaceutical and other process industries. Tablets & Capsules May 2015 19 LIW feeders are a must for continuous manufacturing. In batch operations, they can feed two or more ingredients, reducing cycle times.