CD Basis Weight Control, Facts Explained and Experience Gained, 1998 Process Control, Electrical & Info. Conference Proceedings

Automatic cross directional control of basis weight on paper machines has been a practical working tool for the machine tender for almost twenty years. On the common fourdrinier type paper machine, the cross directional control task requires a thorough understanding of the principles for controlling the profile. The machine tender, or the automatic system, has to utilize a complex basis weight response with several large peaks and valleys and determine what actuators should be adjusted and by how much. Indeed a difficult task with many pitfalls. Lately new and better headboxes as well as more advanced measurement systems have been developed which have changed the way the profile is controlled on those machines. Still, on standard fourdrinier machines controlled by the slice lip, it is essential to understand the implications of a broad basis weight response, and to realize the limitations of the traditional scanning sensor system as well as its effect on the basis weight profile two-sigma. This paper also looks back on some of the myths that have prevailed in the paper making comunity based on exoeriences from the installation of the worlds first model based CD control svstem.