What is a Weigh Module?
Weigh modules are a combination of a load cell and hardware used to support and weigh a vessel or structure. They are commonly used in weighing applications where a bulk amount of material is being transferred or stored in a vessel and the amount of that material needs to be measured or recorded.
Determining if a Weigh Module is Suitable
Before a weigh module can be used with a bulk container, or structure, the structure itself has to be suitable for being converted into a scale.
Before use, consider:
Is the structure rigid enough to be supported by singular points around the perimeter of the vessel?
Most tanks or hopper systems that get converted into a scale are circular or rectangular and are supported by 3 or 4 weigh module locations.
Circular tanks do best with 3 support points; square/rectangular do best with 4 support points.
Will the weighing structure sit on top of the floor, through the floor, or suspend from an overhead structure?
There are a wide variety of weigh modules from many different manufacturers. Each has their benefits based on their design and how they are used.
Generally speaking, they are either used in compression or suspension. Compression modules hold the vessel up. Suspension modules support the vessel from above.
What does the vessel weigh empty with all components attached and what do the net contents in the vessel weigh?
Before you talk with your scale expert, it is important to know what the empty vessel weighs with all mixers/agitators/blenders and external devices attached. This is important in determining what capacity weigh module you will need.
The net weight of the material in the vessel also needs to be determined to size the weigh module correctly.Having this information ahead of time really speeds up the specification process when it comes to weigh module capacity.
A quick equation to calculate the weigh module capacity you will minimally need is shown below:
(Vessel Weight + Net Contents Weight) * 1.25 = Total Gross Weight of your vessel with a 25 % safety factor
You then take the Total Gross Weight of your vessel and divide by the number of support locations to determine your minimum capacity for each weigh module.
For example:
Vessel Weight: 1000 lbs
Net Contents Weight: 10,000 lbs
Total Gross: (1000 + 10,000) * 1.25 = 17,050 Total Gross with a safety factor of 25%
Then using the information above...
If your vessel has 4 supports, you would take 17,050 and divide by 4 for a results of 4,262 lbs per weigh module (minimum).
If your vessel had 3 supports you would take 17,050 and divide by 3 for a result of 5,683 lbs per weigh module (minimum).
Is the site suitable for supporting the use of weigh modules?
A weigh module installation is only as good as the base that supports the vessel. The modules need to be installed on the same level plane and not deflect or deteriorate the structure that is supporting them. If it is out of level or deflects/deteriorates the support structure when the vessel is being used, the system will not perform as expected.
Selecting a good location for the weigh module system may require structural engineers to make sure that it is suitable for the loading that will occur when supported by the weigh module hardware. Generally speaking, the smaller the weigh module hardware, the more point loading will occur on the support structure.
For example, this means that a concrete surface may need to be reinforced or thickened to assure it does not break or deteriorate once the full weight of a vessel is being supported by just a few weigh module locations.
What piping and external factors should be considered?
Piping has adverse effects on weighing since the vessel is a scale and the piping is mounted to it and anchored somewhere else.
This is comparable to placing your hand on the counter when you are weighing yourself on a bathroom scale. The effects of your arm being partially supported by your hand on the counter changes the weight you see on the scale.
Does the location of the vessel allow access for installation, service and testing?
While determining the location for your weighing system, consider the access to each module for installation, along with necessary maintenance service and calibration/testing.
Test weights are heavy and cumbersome and require additional hardware to move them around. If the scale location is too close to a wall or other plant equipment, it could mean you don’t have a method to install or verify ongoing performance of the system.
All effort should be made to select a location that allows your weighing system to continue performing as desired. Your scale expert can help in making this determination via a site visit or site pictures.
Are there provisions for testing the vessel with external test weights?
The testing and validation of the performance of the tank system is the key to having a functioning, reliable weighing system. The ability to hang or support test weights as part of the design of the weighing vessels is critical as a design consideration.
There are many ways to accomplish this. This is most commonly accomplished by mounting support lugs to the vessel to hang weights or by installing a cross braces that are designed to support the external weight without damaging anything to safely support the weights.
Failure to consider testing and validation will nullify any process improvement that you wish to accomplish by installing weigh modules under a vessel. Your scale expert and his experienced service staff can help develop a calibration and testing plan that will meet your weighing system performance needs.
What type of application is it?
To specify, this question relates to what type of weight display/weighing terminal will be attached to your weigh module system.
Tanks with agitation should consider a terminal with excellent filtering. If an agitator is running while material is being added to the vessel, the weight value tends to jump around. Having good filtering in the weighing terminal levels out the weight display so proper target weight values can be met accurately.
If the vessel is to be used for batching or formulation, specially designed terminals can be used to control material transfer hardware and batch values. When using a batch process terminal, the whole system can be automated with documented results of your final batch when its complete. This is a very good way to improve your overall process performance and it provides valuable production data regarding what was put in the vessel as an audit trail.
Need Help or Want to Know More?
Plenty of support help and documentation is available on our website and via our factory trained sales and service staff. Please don’t hesitate to contact us if you are considering using weigh modules to improve your production process. Our experience with Lean Manufacturing and Process Improvements can help you justify funding your project.
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