PROCESS MONITORING WITH MULTIPLE PRODUCT GRADES

In the continuous process industries, multiple grades of the same prod uct are often made on the same production equipment. Key product prope rties for each grade are usually monitored separately because of inher ent differences among grades. Although highly effective in detecting c hanges that affect individual grades such as changes in grade-specific raw material properties, this approach is usually slow in detecting c hanges common to all grades such as a drift caused by production equip ment or changes in common raw materials. The case study of this paper illustrates a simple method of combining and monitoring data from mult iple grades allowing speedy detection of changes affecting all grades and yet still permitting differentiation of overall process shifts fro m grade-specific shifts.