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the problem, disconnect the capsule polisher and catch capsules directly at the ejection chute and weigh them while tracking which capsules came from which segment. This is easy to do because the location of the disc at the transfer station will always correspond to the segment at the ejection station. Note: If the problem is a damaged spring or tamping pin, there could be weight variation at every segment. Method, measurement, and people There are multiple combinations of settings that will produce capsules of the same average weight. But more important than the average weight is the relative standard deviation (weight variation). To prevent wide variation, choose an appropriate dosing disc for each of your prod- ucts. Next, make sure the operators are trained to identify the appropriate powder level in the bowl and how to set it. The same goes for pin penetration. Here's an example to illustrate my point about average weights versus weight variation. Imagine the target is a gross fill weight of 648 milligrams in a size 0 capsule, and four different operators are seeking to meet it. To do so, each operator uses different settings, and they all obtain the target average weight. Good, right? Not so fast. Look at the differences in standard deviation in Table 2. Only Operator 3 succeeded in running the filling process correctly. Observations: • Operator 1 relied on the volume that a very thick disc provides and got some very high and low individual weights. That happened because the machine couldn't form a clean, transferrable slug. • Operator 2 ran the process with too little product in the bowl, so coverage over the dosing disc was uneven. • Operator 3 achieved a very low relative standard devia- tion by using the proper disc, bowl level, and pin settings for this formulation. These are the best results. • Operator 4 used an undersized disc and compensated for it by overworking the tamping pins and springs, which could damage those parts and others. Mother Nature Humidity, because it contributes to making powders sticky, is a common cause of weight variation on tamp- ing-style fillers. Just as flour sticks to a mixing bowl when a little water is added, powders exposed to overly humid conditions can adhere to the tamping pins (photo). That may sound extreme, but I recall running a product trial where the relative humidity in the filling room exceeded 60 percent., and weight variation was a big problem. After we brought in some dehumidifiers, the RH dropped to 40 percent and the powder was much easier to fill. Conclusion A variety of conditions can lead to weight variation, but you can identify them and fix them. Instead of leaving it to chance, address the areas outlined in this article with your operators, formulators, and maintenance technicians; that's the first step to improving your process. For more training, contact your capsule supplier's technical service department. T&C Acknowledgment Brian Dexheimer and Robert Jennings provided photos for this article. 12 January 2017 Tablets & Capsules Table 2 The impact of settings on relative standard deviation of filled capsules that meet average weight Operator Disc thickness (mm) Fill level of powder bowl Penetration depth of tamping pin (stations 1-5) Average weight (n=10) Relative standard deviation 1 24.5 Full 2, 4, 0, 0, 0 648 mg 28.21 2 23.5 1/3 0, 2, 4, 6, 8 648 mg 17.11 3 21.8 3/4 0, 3, 6, 9, 12 648 mg 4.57 4 20 Full 5, 9, 12, 15, 15 648 mg 7.88 Excessive humidity can cause powders to adhere to the tamping pins. Figure 3 Typical configuration of a tamping-style machine's index table and dosing disc Capsule tooling