These systems provide very cost effective and simple level measurement solution in case of bulk solids. This method of level measurement is generally applied in fields are used in applications where level of the material changes very frequently.
They determine level by converting it into volumes and weights. “Converting a distance into a volume requires an assumption of the relationship between the point on the surface of the material where the level measurement sensor will make its’ measurement and (given the angle of repose) the “theoretical” surface height for that same volume of material if the surface were flat and horizontal.”
These systems provide extremely accurate results for distances below 30 feet. For longer distances and higher accuracies, other techniques are required to be employed though with an increase in cost. These level detectors mostly consist of fixed components and hence free from maintenance and part wear.