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Bulk Material Weighing Systems in Production Processes
Why use weighing systems instead of volume measurement or tracking product levels to determine quantity? Weighing systems offer immediate visibility of product levels with a high level of accuracy. Additionally, weighing systems can be easily integrated into bulk material production processes with minimal impact on the existing product lines.
The Basics of Bulk Weighing Systems
Load cells and mounts form the base of weighing systems. The mount helps ensure vertical forces align on the load cell for correct measurements while also ensuring any horizontal forces don’t damage the load cell. There are many different styles of mounts, and the application environment and requirements will determine the style used.
When a system uses more than one load cell, the signals are combined in a junction box to present one weight reading. The junction box is connected to a digital weight indicator or controller to display the weight or transmit the information to another area of production. Weight can be transmitted to a PLC or PC, and special software is used for batching systems, loss-in-weight dosing systems or belt scales. Connections through Profibus, Profinet, Ethernet and DeviceNet allow more data to be shared between a PLC and weight processor.
Static Weighing Systems
Static weighing systems are one of the most accurate ways to determine the net content of a bunker, drum, hopper or large bag in kilograms or tons. The type of load cell and mount used are determined by a variety of considerations including gross and net weight, vibrations, cleaning methods, exposure to corrosive substances, ATEX zoning and more.
Choosing an indicator or controller to pair with the system depends on your needs for functionality, communication to a PLC, where it will be located and how it will be mounted. Some controllers can be installed in production areas while others will be in a control office. Calibration can be performed with a premeasured amount of material in the container or with certified calibration weights. For Legal for Trade weighing, calibration weights must be used to verify weighing system accuracy.
Silo weighing systems are very similar to static weighing systems. However, when the silo is installed outside there are additional conditions to consider for the installation, including strong winds. Special load cell mounts can compensate for high wind forces while providing accurate weights. The mounts are fitted with anti-tipping features to help protect and prevent silos from tipping over.
For many larger silo weighing systems, it’s recommended that an indicator with an auto-calibration function be used to simplify calibration procedures. When load cell data can be entered and stored in the indicator, the calibration can be performed without weights or material.
Belt scales are installed on conveyor belts to easily monitor the amount of material being moved or loaded onto a truck or barge. Using relatively short conveyor belt scales allows operators to control the flow of material, keeping the supply to machine or production line constant.
Screw weighers can be used instead of belt scales with the advantage of creating an enclosed system. This means screw weighers are used primarily for weighing dusty material such as animal feed, cement and fly ash.
A throughput weigher, also known generally as a bulk weigher, allows for a continuous bulk flow of material to be briefly interrupted when performing batch weighing. Two hoppers are installed, one on top of the other, in the transport route with a shut-off valve on each hopper. The bottom hopper is weighed with three or four load cells while the top hopper acts as a buffer while the bottom hopper is being weighed.
The main advantage of a throughput weigher is that it measures continuous material flow with the same level of accuracy as static weighing. However, these systems do require greater height space be available before installation.
Loss-in-weight systems weigh a hopper and attached conveyor mechanism to monitor weight loss in kilograms per hour and determine capacity. The capacity is continuously compared with a configured setpoint or the minimum capacity. If the actual capacity deviates from the setpoint, the conveyor speed is adjusted, and when the hopper is almost empty, the system will pause the conveyor so the hopper can refill and the dosing system can operate continuously. Loss-in-weight systems are ideal for dosing powders and granulates in capacities of 1 to 1,000 kilograms per hour.
Choosing the right dosing system for your needs can feel overwhelming with so many options available. Working with an industry expert can help you determine the best system for your business, including specific load cells and mounts to meet your requirements. Rice Lake Weighing Systems has an experienced team of weighing system experts available to help you understand all the options available to you.