2.0 General Release Check

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Sidebar Figure 1 illustrates the Smart Refill Technology (SRT) approach. The graph at the top plots net hopper weight versus time.  Beginning with a full hopper (where net hopper weight equals refill complete weight) gravimetric operation is in effect, and the feeder operates normally. As net hopper weight declines, the controller also determines and stores a set of up to 100 feed factors, each of which is the index of the average density of material discharged at the hopper weight associated with the feed factor. A low feed factor indicates that a higher number of screw revolutions were required to discharge a given weight, implying a reduced material density. Conversely, a higher feed factor reflects higher density because fewer revolutions were required to deliver the same material weight.

The middle plot of Sidebar Figure 1 shows motor speed versus time. During the early portion of the gravimetric feeding phase, motor speed is relatively constant because density within the metering zone of the feeder, while higher than at later times in the feeding cycle, does not vary substantially. This is because material in the upper portion of a typical hopper is largely supported by the material below, and, in turn, the tapering walls of the lower portion of the hopper. As feeding proceeds and hopper level declines, headload in the metering zone begins to lessen, resulting in a reduction in density and a corresponding increase in motor speed required to maintain feed rate. When hopper weight reaches the refill request threshold, the refill phase begins. During refill, SRT begins with the motor speed that was in effect at the time of the refill request, and then modifies that speed by applying the corresponding feed factor as each hopper weight “slice” is encountered. 

By taking this more sophisticated approach, it is possible to smoothly exit the refill phase and return to true gravimetric operation. Additionally, by controlling feeder speed during refill based upon the most recent performance history, reverting to volumetric performance is avoided and gravimetric accuracy is essentially preserved.

Sidebar Figure 1: The smart refill control concept.

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Sidebar Figure 1 illustrates the Smart Refill Technology (SRT) approach. The graph at the top plots net hopper weight versus time. Beginning with a full hopper (where net hopper weight equals refill complete weight) gravimetric operation is in effect, and the feeder operates normally. As net hopper weight declines, the controller also determines and stores a set of up to 100 feed factors, each of which is the index of the average density of material discharged at the hopper weight associated with the feed factor. A low feed factor indicates that a higher number of screw revolutions were required to discharge a given weight, implying a reduced material density. Conversely, a higher feed factor reflects higher density because fewer revolutions were required to deliver the same material weight.

The middle plot of Sidebar Figure 1 shows motor speed versus time. During the early portion of the gravimetric feeding phase, motor speed is relatively constant because density within the metering zone of the feeder, while higher than at later times in the feeding cycle, does not vary substantially. This is because material in the upper portion of a typical hopper is largely supported by the material below, and, in turn, the tapering walls of the lower portion of the hopper. As feeding proceeds and hopper level declines, headload in the metering zone begins to lessen, resulting in a reduction in density and a corresponding increase in motor speed required to maintain feed rate. When hopper weight reaches the refill request threshold, the refill phase begins. During refill, SRT begins with the motor speed that was in effect at the time of the refill request, and then modifies that speed by applying the corresponding feed factor as each hopper weight “slice” is encountered.

By taking this more sophisticated approach, it is possible to smoothly exit the refill phase and return to true gravimetric operation. Additionally, by controlling feeder speed during refill based upon the most recent performance history, reverting to volumetric performance is avoided and gravimetric accuracy is essentially preserved.

Sidebar Figure 1: The smart refill control concept.