A major Biotechnology manufacturer based in Massachusetts had been experiencing challenges with conventional strain-gauge load cell performance in a static mixing tank application. The tank in question is a 300L mixing tank with three legs that has a large hinged-lid design. Opening and closing of the lid was causing challenges; the movement of the mass of the lid was causing the tank to shift on the load cells, resulting in binding on the load cell mounting kits. The unpredictable binding caused expensive deviations and the client needed a solution.
The existing installation used three strain-gauge style load cells along with mounting kits and guide rods that are commonly used with this style of cell. These kits are often necessary to physically protect the strain gauge sensing element within the load cells from side-loading and overloading which can occur during use. When these kits are employed, it is imperative that the kits are mounted and aligned properly so that the load is able to move freely. Otherwise readings can be inaccurate or inconsistent as this client was experiencing.
The situation came to light during a presentation of the Alfa Laval Capacitive Weighing technology. The Alfa system relies on a capacitive sensing mechanism rather than a strain gauge element which means that the sensor is not physically connected to the weighing beam. As a result, the Alfa system is much more robust; it can handle extremely high side and over-loads meaning that the cell does not need the protection of an extraneous mounting kit. Eliminating the requirement for a kit means that the installation is much more straightforward, easier to clean, and cannot introduce binding as is common with strain gauge systems.
There remained a challenge, however. The client needed to insure that changing the cells over could be accomplished in a few short days with no welding, machining, or tank modifications in the clean suite. In addition, they needed to maintain exact vessel height so that they did not need to modify any piping or wiring that connects the vessel. Alfa Laval was able to fabricate custom mounting plates to match the height and bolt patterns exactly, and most importantly we were able to have equipment on-site to meet their stringent installation window.
To date, the system has been installed for approximately two years with zero observed deviations. Calibration has remained constant and the client has been satisfied. As a result, to-date they have installed ten (10) new systems in similar applications throughout the facility.
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