Processing, Dec 2012

flat surface profile or shape Some materials due to the vessel design and flow properties may appear to flow like a liquid but they do not Proper vessel design however can aid in reducing the effect of this solids challenge to calculating the volume and weight of a bulk solid from a level measurement with a reasonable degree of accuracy The irregular and angled material surface profile or angle of repose of a powder or bulk solid presents a challenge for the accuracy of the calculated volume and weight because the level measurement sensor measures only at a single point on the surface of the material Any calculation of volume and weight based on the single point distance level measurement will assume you remember the old saying about assume a flat surface because nothing is known about the profile The flatter or more regular the material surface actually is the more accurate and precise the calculated volume can be This also improves the accuracy of the calculated weight volume x material bulk density but that calculation also is impacted by bulk density accuracy Final words I know we havent gone into great depth here about weighing silo contents and the wide variety of level measurement technologies I refer you to the book titled Solids Level Measurement and Detection Handbook copyright 2012 by Momentum Press LLC all rights reserved for further and complete information However it is worthwhile to excerpt a table from Chapter 5 of the referenced book which is reprinted with permission on page 18 to illustrate the differences between the two choices measuring weight or level Be preemptive and cautious about the need for and choice of an inventory measurement strategy for powder and bulk solids kept in a silo or bin Do you need inventory measurement for the purposes of your business accounting If yes then consider this up front and choose weight measurement over level measurement However if you are more concerned about whether you have enough room to replenish the material in your silos or you just need to control the filling cycle then the level measurement sensor with the lowest cost of ownership or even simple level control point level devices would be the best choice Joe Lewis is managing director of BlueLevel Technologies 1741 Industrial Drive Unit 5 Sterling IL 61081 888 61LEVEL 53835 815 625 2224 joe@ blueleveltechnologies com If you have any questions you can reach him by email or phone Blue Level Technologies www blueleveltechnologies com Write In 552 20Level Measurement Write In 214 December 2012 www ProcessingMagazine com