Hello, McFly! Is anybody in there?
Why is sensor selection usually the very last thing that gets considered when new silos are ordered. Having said that, many times level sensors are not even thought of until the silo has been erected on site. Then there is the "we will have to modify the silo to accommodate level sensors crisis". Perhaps the silos were already cleaned and there is some material already being stored so cutting and welding is out of the question. Etc., etc., etc.
Too late for load cells and you didn't like the price tag anyway. So, I guess we will have to settle on a sensor that measures the empty air space and then calculates the volume and weight and make compromises to fabricate a process connection. Too often these days, I am seeing more and more new silo installations with fill points that are not in the center of the vessel. Every level measurement technology out there, except gravimetric, measures the distance (air space)between the sensor and a point of intersection on the material being measured. If the vessel is truly centerfilled and the level sensor is mounted at 1/6th the diameter from the outer wall on the radius, the calculated volume and or weight of the material will be very close to actual assuming all dimensional data and the bulk density data are accurate. Follow this link and download item 3 for complete details regarding sensor placement and accuracy of calculated volumes and weights: http://www.monitortech.com/wseminars.shtml One word of caution is that some silo manufacturers consider center filled to be a fill point that is located anywhere within a circle defined as less than one-third of the radius. This is not good enough if you are striving to maximize the calculated accuracy.
Finally,remember to add an independent self-validating point level sensor to alert you when your silo is full and to prevent over-filling and potential spills, even those due to unknown sensor failure. Refer to other posts within this blog.
Greg DeRudder
Technorati Tags: level sensor level measurement bin level indicator level control solids level indicator
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