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Stockpile Tracker
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The software does not model the mound as a simple triangular prism shape (elongated pyramid). The shape of the floor and the action of the scraper(s) create irregularities. To capture this, the algorithm calculates detailed cross-sections that differ based on whether the mound has been scraped, the shape of the floor, and how scraping has affected the shape. The model consists of a series of one-meter-wide cross-sectional slices.

one-meter-wide cross-sectional slices
Figure 1 – Sketch of the one-meter-wide cross-sectional slices that form the model.

cross-section that has been scraped
Figure 2 – A cross-section that has been scraped, showing compacted material along the floor.

The figures above show how Stockpile Tracker calculates a complex shape for each cross-section, depending on the shape of the floor under the mound and how the upper parts have been scraped.

Since urea may compact over time, Stockpile Tracker can be configured to treat bottom material as compacted, off-spec and “Unusable.” The crosshatched regions in the above example represent off-spec, compacted urea that can’t be scraped and shipped. Users may configure a certain number of meters at each end of the mound floor as consisting of off-spec material too, since the material at the extreme ends of the warehouse may be difficult to ship and compact over time. The total amount of unusable tons is shown separately on the main display.

For areas of the mound that have been poured but not yet scraped, Stockpile Tracker takes into account the rounded top of the mound. It assumes a slightly flattened top for areas that have been poured but not yet scraped. This greatly reduces the size of the error introduced by the presence of the pile’s rounded crest (see figure below):

slightly flattened crest e
Figure 3 - Assuming a slightly flattened crest eliminates most of the error
caused by the curvature.

Stockpile Tracker, with appropriate tuning, can produce surprisingly accurate results. An early study found that, over several weeks, Stockpile Tracker’s estimate of produced granulated solid agreed to within 0.05% with the production as calculated by the customer’s technical department. Overall inventory should be calculable to within 2% of mound or warehouse capacity.

The model’s accuracy is limited by, among other things, the accuracy of the pile height sensor. Urea, in particular, creates a lot of dust. This can limit the choice of sensor technology (to ultrasonic sensors) and interfere with accuracy when the mound is low. Fortunately, a low mound is usually a temporary condition.

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