Method and apparatus for on-line web property measurement

Measurement apparatus for measuring at least one property of a web of material as said web is being manufactured and is moving in a machine direction (MD) by scanning said measurement apparatus back and forth across said web in a cross-machine direction (CD), said apparatus comprising:

• a source of measuring radiation appropriate for measuring said at least one property, said measuring radiation being directed toward said web;
• at least first and second sensors that receive radiation from said web and generate signals representative of said radiation;
• at least one pyrometer that measures temperature of said web;
• and
• a shutter mechanism that interrupts said source of measuring radiation when said sensor is positioned on an edge of said web wherein said sensor generates signals in response to measuring radiation representative of said at least one property and Planckian radiation when said source of measuring radiation is uninterrupted for each of consecutive points extending across said web between edges of said web and said sensor generates signals in response to Planckian radiation for at least one of said edges of said web while said source of measuring radiation is interrupted, and said pyrometer measures a temperature for each of said consecutive points extending across said web and for at least one of said edges of said web;
• and
• a controller that develops correction factors for said at least one property for each of said consecutive points across said web from a measured edge temperature and the measured temperatures of each of said consecutive points across said web, and applies said correction factors for each of said consecutive points across said web to correct for Planckian radiation contained in radiation sensed for each of said consecutive points across said web.

Measurement apparatus for measuring at least one property of a web of material as said web is being manufactured and is moving in a machine direction (MD) by scanning said measurement apparatus back and forth across said web in a cross-machine direction (CD), said apparatus comprising:

• a source of measuring radiation appropriate for measuring said at least one property, said measuring radiation being directed toward a first side of said web;
• beam splitting apparatus that receives radiation from a second side of said web opposite to said first side, said beam splitting apparatus having a radiation input port directed toward an area of said web irradiated by said measuring radiation and at least a first output port and a second output port;
• a first sensor that receives radiation from said first output port of said beam splitting apparatus and generates signals representative of received radiation;
• a second sensor that receives radiation from said second output port of said beam splitting apparatus and generates signals representative of received radiation;
• a pyrometer that measures a temperature of said web;
• and
• a shutter mechanism that interrupts said source of measuring radiation when said sensor is positioned on an edge of said web wherein said first and second sensors generate signals in response to measuring radiation and Planckian radiation when said source of measuring radiation is uninterrupted for each of consecutive points extending across said web between edges of said web and said first and second sensors generate signals in response to Planckian radiation for at least one of said edges of said web while said source of measuring radiation is interrupted, and said pyrometer measures a temperature for each of said consecutive points extending across said web and for at least one of said edges of said web;
• and
• a controller that develops correction factors for said at least one property for each of said consecutive points across said web from a measured edge temperature and measured temperatures of each of said consecutive points across said web, and applies said correction factors for each of said consecutive points across said web to correct for Planckian radiation contained in radiation sensed for each of said consecutive points extending across said web between said edges of said web.

A method for measuring at least one property of a web of material as said web is being manufactured and is moving in a machine direction (MD), said measuring apparatus comprising a source of radiation appropriate for measuring said at least one property that is directed toward said web and at least first and second sensors that receive measuring radiation from said web, said method comprising:

• receiving radiation representative of said at least one property of said web from at least one point in the cross direction (CD) of said web;
• measuring temperature at said at least one point in the CD of said web;
• interrupting said measuring radiation;
• sensing radiation received from said web while said measuring radiation is interrupted;
• measuring temperature of said web while said measuring radiation is interrupted;
• developing correction factors for said at least one property from said temperature measured while said measuring radiation is interrupted and the measured temperatures of said at least one point of said web;
• and
• applying said correction factors at said at least one point of said web to correct for Planckian radiation contained in radiation representative of said at least one property of said web received at said at least one point of said web.