There are a lot of options when it comes to tank, hopper, or silo weighing systems. It can be a daunting task trying to choose the correct weigh modules and capacity load cells for your particular needs. This is when it is imperative to talk to an experienced load cell sales technician. Don’t guess, don’t buy online without talking to an expert first. This is where Load Cell Systems excels, specializing in vessel weighing. We can assist you not only in choosing the correct load cells but the associated electronics needed for your application.
To get you started, the basics of these weighing systems follows:
Choosing a load cell capacity, many factors affect this decision. For example an indoor 4 leg tank is weighing a liquid (self leveling product) your total load cell capacity should be approximately 20% over the tank weight and maximum amount of product. If the vessel is weighing product that is being dumped in and may shock load the scale or may have a large motor or mixer hanging off one side of the tank, you’ll want to increase the load cell capacity as needed. Outdoor vertical silos subject to high winds, we recommend over rating the load cells to 50-70% over the total capacity (always consult an engineer when working with this type of system or if the installation is in a seismic area).
Some people will want to cut cost by only installing 1 or 2 load cells under the vessel’s legs instead of supporting all of them. This is an option, though we don’t recommend it if any type of accuracy is needed for the scale. This is only feasible for self leveling material, and a typical accuracy of such a system may be around 1-3% of the total capacity.
Load cell installation, all of the load cell mounts must be on the same plane. The height of the weigh modules will need to be adjusted or use shims to accomplish even loading on each cell. The installer can also measure the output of each load cell to make sure the load is balanced. Some of our electronics such as the TLM8 load cell amplifier, or the CLM8 digital junction box will show the individual % of load on each channel, this makes installation easier and faster.
The load cells either connect to a load cell junction box then connected by a single cable to an instrument or a multi-channel amplifier can have all the load cells wire directly to it without the need of a j-box. The choice of the instrumentation varies greatly on the user’s needs, it can be as simple as an amplifier outputting an analog or digital signal to a PLC, or a full fledged multi-ingredient batching controller with I/O control.
Plumbing to the vessel, it is important to ensure there is no binding in the system caused by the piping. The vessel must be free standing not attached to other structures by catwalks for example. It is ideal when the fittings are free floating, or bellows that allow vertical movement. If flexible connections are not feasible, try to keep the pipe mounting hardware as far away from the scale as possible. This allows for deflection in the pipes which will cause less error in the scale.
System calibration, Load Cell Systems can pre-calibrate these systems (it is required the calibration is verified with known weights after the install, in case of mechanical binding issues) this method can save tons of time. The load cells are typically wired to the j-box or indicator when received as long as it can be shipped safely assembled. Alternatively an in-the-field calibration is done with either test weights or by filling the vessel with a known amount of product, this is typically the more accurate way to go if high accuracy is required.
Vessel Weighing Conclusion:
This is a very general article on the subject, there are so many variables it’s almost impossible to write an all encompassing “how-to” guide on the subject. Again we always recommend consulting an experienced sales technician before any purchase of a vessel weighing system.