While flow meters and load cells are two very different technologies, their paths may sometimes overlap. In fact, it is not always easy to decide which technology would be best suited for a certain application.
For instance, when outfitting a tank for batching, you must select a method for measuring the amounts of each ingredient added. A flow meter may be the first device that comes to mind. However, the load cell might actually be the better solution.
A flow meter may come in many forms, but it is usually an in-line device that measures the rate or flow of a fluid—either in volume or mass. On the other hand, a load cell is a device that allows for the contents of a tank or vessel to be weighed.
A flow meter can be a great solution in many applications. Flow meters work at their best when measuring continuous flow, rather than frequent starts and stops, and they are great for bulk receiving by weight or volume (depending on the meter). A variety of system checks and balances can also be performed with flow meters, from ensuring adequate flow rate during CIP cycles, to helping to regulate the flow of a pump.
So, when is a load cell system a good solution? Precise batching comes to mind.
Because a flow meter is located in the tubing upstream from a tank, there is a difference between what the meter reads and what is truly in the tank. Programming changes can correct for the delays in measurement caused by this difference, but they can be imprecise and require frequent calibration.
However, because a load cell measures the weight of the tank itself, delays are minimized. Load cells offer a particular benefit when dealing with products that don’t usually work well with flow meters. Liquids with entrained air or bubbles may give meters trouble, but they are no problem for load cells. Even dry ingredients like powders can be measured just like liquid adds using load cells.
In addition, newer “capacitive” load cells (like the shockproof digital load cell from Alfa Laval) offer high accuracy in weighing, and are virtually maintenance free. Unlike traditional load cells, capacitive load cells maintain their accuracy every time they are used, without ever needing to be recalibrated, even over years of abuse.
One downside of using load cells could be that only one ingredient can be added and measured at one time, while using multiple flow meters could allow for simultaneous additions of different products.
In a side-by-side comparison, adding load cells to one tank may initially cost more than one flow meter. However, if multiple flow meters are needed for each tank, the initial investment can often be lower for a load cell setup. After the initial investment, load cells can pay for themselves by minimizing ingredient waste and quality issues due to batching errors.
Whether you choose load cells or flow meters for your application, there are many options and styles available that can be customized to suit your needs.