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Want Better Inventory Accuracy? Know YOUR Stuff |
July 07, 2010 |
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Posted by Joe Lewis at July 7, 2010 10:32 PM |
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Use of continuous level sensor technologies like wight & cable, radar, acoustic and others are almost always for inventory monitoring purposes when used with powders and other bulk solid materials. In these inventor applications the sensor is used to answer the question, "how much stuff do I have?". Using a continuous level sensor will generally make a measurement of the distance from the sensor to a point on the material surface with good accuracy. But this measurement does not really answer the question. Why? Because you bought or produced the material in inventory storage based on volume or weight.Now you have to convert from distance or perhaps a material level at a single point to volume and then mass. But wait, your material surface isn't flat. Locating the level sensor for measuring distance at the optimum point on the material surface is a key variable to making your volume and mass calculating as accurate and precise as possible. You need to understand your material profile and work with the level sensor manufacturer to determine the best mounting location based on the best level sensing point on the material surface.
What about the material bulk density? Assuming a uniform bulk density throughout the pile of material in your silo may be inaccurate. Your material packs, therefore the bulk density at the top of the pile is somewhat lighter than that at the bottom. In addition, if you are buying this material from an outside source or if you produce the material in batches or lots, the bulk density may vary slightly from batch to batch. This also impacts the accuracy and precision of the calculated weight.
The most practical solution requires you to know your material profile and have a good average bulk density. Other solutions do exist, such as weighing the vessel/contents using a load system or using the latest technology that maps the material surface and accurately determines contents volume.
For additional information check out the below links:
White Paper Continuous Level and Inventory Monitoring of Powders and Bulk Solids
What You Know Can Make All The Difference
Surface Mapping
In addition, you can review an upcoming technical exclusive article in the August issue of Powder Bulk Solids magazine titled "The Problem with Measuring Levels". I'll update this blog with a link when this is available.
Joe Lewis
