Technical Profile: Bulkweighing Systems

by Teresa Acklin
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   Contributed by suppliers, technical profiles feature new technology, products, specific applications or proprietary concepts. This material was prepared by Ray Vrtiska, InterSystems, Inc., Omaha, Nebraska, U.S.

   Bulkweighing is defined as “a multiple hopper system designed for weighing of free flowing bulk materials on a continuous basis with accuracies equivalent to static or manual weighing.” The theory of operation is to have a continuous flow of material in and out and obtain weighing accuracies of 0.1% or better.

   A typical InterSystems bulkweighing system consists of a material handling system and automatic scale controls. The material handling system includes an upper surge hopper, weigh hopper, lower surge hopper, gates, steel structure, load cells and level indicators.

   The upper surge hopper serves as the gathering hopper to feed material to the weigh hopper. The weigh hopper is mounted on load cells and weighs each draft fed. The lower surge hopper receives each draft from the weigh hopper and then discharges it into a vessel such as a rail car, ship or truck.

   A gate is located above and below the weigh hopper to control the feed and discharge of material. Level indicators are used on each hopper to indicate material levels that are monitored by the controller. This complete system is framed up and supported by a steel structure.

   The most popular type of InterSystems material handling system is a factory assembled unit including the pre-wiring of electrical components, pre-plumbed valves and cylinders, assembled structure around hoppers and the enclosure. All functions are controlled by an Agris oneWeigh automatic scale control unit, which contains the scale indicator and microprocessor.

   Technology in these controllers includes not only the ability to monitor and record the weighing process but also downloading of the data to a host computer and controlling other operations within a plant. Agris provides an on-line modem service connection for updating programs and assisting in answering service questions.

   Operation of this system is very simple. A desired target weight is placed into the controller and a “start” is initiated. A draft is fed into the weigh hopper from the upper surge hopper, and when a predetermined draft size is reached, the feed gate is closed.

   A gross weight is recorded and then the material is discharged from the weigh hopper into the lower surge to flow away at a controlled rate. A tare weight is taken on the weigh hopper to provide a “net weight” delivered.

   The upper surge has continued to accept material from a feeding device so that it is ready to provide the next draft to the weigh hopper. Upper surge hoppers are designed to suit requirements for run time and cleanout of mechanical feeding devices.

   Each material handling system is properly sized to accommodate the flow rate of material and to account for space limitations. Also, the current trend is to have each model of bulkweighing system approved by weights and measures authorities.

   Bulkweighing systems are the most preferred method of weighing free flowing materials because they offer the following benefits over other weigh mechanisms such as track scales or volumetric measuring devices:

   • speed — there are no delays or obstructions to material flow rates — no need to take a tare weight prior to loading;

   • accuracy — weighing accuracy of 0.1% or better is obtained;

   • recorded weights — each net weight and each total weight is recorded;

   • monitored production — instant feedback on production rates are displayed;

   • cost reduction — better control of inventory and effective utilization of labor;

   • safety — minimal handling of vessels to be weighed;

   • maintenance — limited maintenance necessary; and

   • service — computer on-line service through a modem connection.

   Bulkweighing systems provide the speed, accuracy and reliability that is demanded in today's marketplace.