ACOUSTICS BASED ONLINE QUALITY ESTIMATION

One of the major difficulties with developing advanced control strateg ies for cooking extruders is the lack of cheap, easy to implement, on- line ''product quality'' estimators. One of the most promising develop ments in this area is the recent emergence of acoustics based estimati on techniques. The basis of this approach relies on the fact that as t he extrudate leaves the die, the water content partially flashes causi ng the extrudate to expand. There are discernible differences in sound as this steam escapes when different products are being extruded. It is the interaction between this expansion, the rheology of the extruda te, and the resultant bubble size distribution that gives the final pr oduct many of the qualities that both the manufacturer and the consume r are looking for.-This paper outlines the techniques used to analyse experimental acoustic data and develop correlations to predict final e xtruder product properties. (C) 1998 Published by Elsevier Science Ltd . All rights reserved.