System and process for detecting properties of travelling sheets in the machine direction

A method for determining machine-directional variations in a property of a traveling sheet during production, comprising the steps of:

• repeatedly traversing the travelling sheet with a scanning sensor and during each traverse, taking measurements of a property of the sheet at a plurality of slice locations;
• estimating cross-directional measurement values at reference locations for each scan based upon the actual measurements at the plurality of slice locations;
• for each scan, determining the average of the estimated aligned cross-directional measurement values;
• calculating the cross-directional variations in properties of the sheet at each slide location along the scans by, for each scan, subtracting the average value from the estimated aligned value at each slice location along the scan;
• and
• during the next scan, determining machine-directional variations in the sheet property at each slice location by calculating the difference between the actual measured value and the calculated cross-directional variation value for that slice location along the prior scan.

A method for determining machine-directional variations in a property of a travelling sheet during production, comprising the steps of:

• repeatedly traversing the travelling sheet with a scanning sensor and, during each traverse, taking actual measurements of a property of the sheet at a plurality of slice locations;
• at reference locations, estimating true cross-directional measurement values for each scan based upon the following formula:
• E.sub.j,i =1/2(S.sub.j +S.sub.j +1.sub.,i)
• where E is the estimated aligned value of a sheet property, S is the actual measured value of the sheet property, the subscript i represents the slice location, and the subscript j identifies the scan j;
• determining the average of the estimated cross-directional measurement values for each scan;
• calculating the cross-directional variations in sheet properties at each slice location along the selected scans by, for each scan, subtracting the average value from the estimated aligned value at each slice location along the scan;
• and
• during the next consecutive scan, determining machine-directional variations in the sheet property at each slice location by calculating the difference between the actual measured value and the calculated cross-directional variation value for that slice location along the prior scan.