b'What allfrom each sensor. These are inputsSTART WITH ACCURATE MEASUREMENTS achieve a step change in quality papermakingto the CD controls. The purpose ofIn Honeywells view, the optimaluniformity from existing production applicationsCD control is to minimise the cross- solution for demanding pulp & paperassets such as headboxes, press have indirection variation of measured sheetoperations starts with accurate qualitysections or coaters.common isproperties using one or more CDmeasurement capabilities. Precise the need foractuator beams that span the sheetand reliable measurement sensors areMajor papermaking operations around the fastestand to provide fast profile recovery fromessential for papermaking operationsthe world have found that the right sensorprocess disturbances. because by continuously measuringcombination of measurement sensors, response withsheet properties, they make it possibleCD actuator arrays and control solutions the highestThere are frequently separate handlesto react almost instantaneously tohas enabled them to simultaneously possiblefor controlling weight and moisture inprocess changes, either by operators orimprove sheet properties and reel-accuracy. the cross-direction (across the paperby automated process control. building, along with other associated machine) versus controlling thesebenefits.qualities in the machine direction.Within paper machine operations, Cross-direction quality for each variableeach measurement device has aDEPLOY EFFECTIVE CONTROL SOLUTIONSis commonly referred to as the profiledifferent goal and a different strategyPapermaking is a precision operation. for that variable. Devices that controlfor accomplishing its objectives. TheseWeight, moisture, and thickness of CD or profile variability are known asassets are used to measure productionpaper must be uniform from the start profile controls or profile actuators. variables such as: to the end of a roll and across the width of the sheet. A variety of control CD profiles are controlled using aBasis weight techniques have been developed to number of CD actuator arrays. TheseMoisture maintain the quality of the paperarrays span the paper machine widthThickness (Caliper) not only in the direction the sheet is and may contain up to 300 individualAsh moving, but in the cross-direction as actuators. Common CD actuators arraysCoat weight well.allow for local adjustment, across theColourmachine, of slice lip opening, headboxCrepe The latest MD and CD controls utilise dilution, rewet water sprays, andPorosity multivariable model predictive control induction heating of the rolls. Formation technology to ensure product quality Surface topography and paper machine runnability. These Because paper typically moves in theFibre orientation controls improve the economics of the machine direction at high speeds,Gloss papermaking process through better but the scanning sensors move in theOpacity utilisation of resources and increased cross direction at a considerably slowerCoating production efficiency.rate, the sensors path across the moving sheet is a very low angle. ThisWhat all papermaking applicationsAdvanced MD control algorithms means a single scan across the sheethave in common is the need for theare used to perform a predictive includes both MD and CD variability.fastest sensor response with themathematical material/energy balance As such, cross-direction measurementshighest possible accuracy. State- for overall production improvements. from a single scan rarely reveal theof-the-art paper machine actuatorsIntegrated CD controls employ control persistent profile. Advances in software ensure minimum cross-machine profilealgorithms to systematically achieve the processing in the control algorithmsvariations, thus improving paper qualitybest utilisation of control ranges for all enable the QCS to properly handleand increasing production efficiency. actuators and control sheet property various scan speeds and measurementprofiles at their targets. As a result, resolutions, maximising value from theIndeed, an upgrade in cross directionpapermakers can address multiple MD/CD controls. quality profiling is often needed tosheet profiles and control multiple WORLD PULP&PAPER 57'