Correct continuous weighing of ingredients is essential for reaching the required product quality. If the various ingredients are not dosed in the correct quantities to begin with, it will never be possible to produce a correct product. For that reason, Sobatech dedicated years of time and effort in developing the most accurate weighing technology available.
VOLUMETRIC VS. GRAVIMETRIC
(Dry) Ingredients can be dosed volumetrically or gravimetrically. A volumetric dosing system doses a given volume of material per time unit. The dosing speed of a volumetric feeder should be selected manually, which may vary based on the nature of the raw material input. A volumetric feeder is open-loop in a sense that it does not corrects to variations in the material’s density. A gravimetric dosing system doses the actual given weight of material per time unit. The weight is measured by using load cells which form the foundation of the entire system. In a self-calibrating gravimetric feeder system, the motor automatically alters its speed when a change is detected in the material flow. When using a gravimetric feeder to dose, you are in complete control of the quality of your final product.
LOSS-IN-WEIGHT VS. GAIN-IN-WEIGHT
Sobatech only works with gravimetric feeders based on the loss-in-weight dosing principles. This dynamic measuring principle is the most accurate weighing solution available. The feeders are located on digital load cells that constantly measure the weight reduction per time unit. Based on that information, the speed of the dosing screws is constantly controlled based on a closed loop principle. The system ensures an accurate flow of ingredients during both loss-in-weight (normal operation) as well as gain-in-weight (during refilling).
Sobatech’s software to control the feeder pump and other dosing hardware, ensures a continuous and accurate flow of both dry- and liquid ingredients of low, middle and high viscosity. Measurement equipment such as magnetic and Coriolis flow meters are used to regulate the correct quantity of liquid ingredients entering the continuous mixer. Sobatech can either tap the liquids from a circulating pipeline or from a storage tank.
OPEN SOURCE SOFTWARE
Sobatech developed its own tailor made open source software to control the feeder-pumps and other hardware involved in the continuous dosing of the ingredients. Put differently, in Sobatech’s continuous mixing systems there are no hidden programs nor protected passwords. The complete system is open and accessible to the customer.
GAIN IN WEIGHT
The refilling is done at the assymmetrical location in the dosing hopper to prevent the product from being compressed above the dosing screw. This ensures accuracte dosing even during the so called gain in weight process. The gravimetric dosing hopper is seperated from the fixed world by means of a weighing frame mounted on shock absorbers in order to minimize vibrations and other outside influences.
DIGITAL LOAD CELLS
In order to achieve the highest possible dosing accuracy, all gravimetric dosing units are equipped with digital weighing cells. The weighing cells communicate with Sobatech’s open source software of the PLC through an Ethernet connection. Each dosing hopper is equipped with three digital loadcells and venting filters to eliminate pressure differences.