Feedback Control of the Dry Line on Wire of Paper Machine

Two methods for instrumental measurement of the dry line have been developed. They are based on innovative arrangements of illumination and related observation under which the pulp on wire is seen by video camera as a composition of dark and light fields. The complete dry line is extracted from the image and used industrially for feedback control of the dry line in machine direction (MD). Recorded correlations between changes of dry line and dry basis weight profile justify conclusions on their control in cross direction (CD) and on incorporation of dry line measurement into conventional MD and CD controls which are handicapped by a long process delay.