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As with any new process there are always a number of challenges. In this case they are associated with dispensing and weighing accuracy, mixing and scalability.
Hanging load cells were selected because the system is so dependent on accurate measurement and control. Overcoming the dispensing and weighing accuracy challenges were critical to the project's success. As a result, the selected load cells had the following features:
After some research, the selected weighing solution was a cantilevered weigh cell manufactured by BLH (http://cimail15.blh.com/process-weighing/). The KIS 3 Load cell is unique in that its "double" cantilevered design as shown in Figure 2 locates the load force application point directly above the strain gauges. This provides the following:
Liquid ingredient addition (whereby the liquid has similar fluid characteristics to water) is volume added based on mass, with known specific gravity and starting and resulting concentrations. Weigh cells are a suitable measurement technology for this application as the multiple, changing masses of the ingredient additions require an in-line, multi-channel weighing instrument with panel readout.
These load cells are converted from strain gauge transducer signals to weight information using a G4 multi-channel weighing instrument. As a result, the measurement signal represents the only true applied force, thus making it possible to achieve the measurement accuracies required for this installation.
As this process migrates to larger scale production, it will be necessary move to larger bags which, due to their weight, will have to be supported with a more rigid floor-mounted structure. Fortunately, the BLH weighing system, forming a key part of the process and control system, can also be scaled to this configuration.
Accurate sensing and control is a critical part of the development of new biopharmaceuticals, not only to maximize return on investment through the elimination of reprocessing and remanufacturing, but also providing proper measurements to meet the strict documentation requirements and cGMP constraints for approval of products undergoing clinical trials.
Opportunities arise as the industry moves from stainless steel setups with fixed probes, to flexible and disposable mixing and reaction vessels, which require high-accuracy measurement irrespective of holding vessel geometry.