Solids flow measurement by correlation methods

The flow velocity of the solids content in pneumatic conveyors is determined from the transit time between two fixed points. Transducers located at these points generate random signals due to the naturally occurring random flow patterns. A special correlator is used for cross-correlating the transducer output signals and for automatically tracking the transit time. The correlating device is simple enough so that a rugged, reliable and yet precise field instrument can be built. Using optical or capacitive transducers, the average velocity of the solid content is measured without obstructing the flow profile. Under certain restrictions, the mean loading and thus the volume flow can be determined from the same sensor signals also. The effect of sensor geometry on bandwidth and the choice of optimal sensor distance is discussed. Optical and capacitive sensors are compared. Illustrative experimental results are given.