Nuclear gauge for measuring a characteristic of moving sheet material and alignment compensation
AssigneeImpact Systems, Inc.
InventorPekka M. Typpo
Life of this patent
Estimating the term…
Abstract
For measuring basis weight of a moving web in the cross direction scanner of a paper-making machine, an encapsulated nuclear source of Promethium 147 is used because of its wide area of emission. To conserve space it is mounted on a vertical axis. The source in a horizontal plane parallel to the moving web from a stowed position where the source is shielded to an active position where the source emits through an aperture, through the moving web, and to a detector. The x-y array planar type detector uses four detector segments symmetrically arranged around a center and compensates for belt direction misalignment (the belt driving the cross direction scanners) by mathematically manipulating the electrical signals from each detector to eliminate the error term.
Claims10
Apparatus for measuring a characteristic of a moving web of sheet material having a pair of transducers on opposite sides of the web the pair of transducers being scanned across the web the apparatus comprising:
- one of said pair of transducers having an aperture with a center axis perpendicular to said web and in close proximity to said web and including an encapsulated radiation source which in a first position emits radiation along a radiation axis substantially coincident with said center axis through said aperture and through said web to the other of said pair of transducers, said other transducer including detector means for sensing radiation received through said web from said radiation source,
- means for mounting said encapsulated radiation source for movement in a plane perpendicular to said radiation axis and parallel to said web from an axis of movement, offset from said center axis, between a stowed position where said radiation from said radiation source is shielded to said first position.
In a multi-segmented planar detector having three or more segments for use in measuring a characteristic of a moving web in conjunction with a radiation source on the opposite side of the web having a radiation axis where the source has a relatively large area of radiation emission, each of said segments being symmetrically arranged around a center detector axis which is nominally coincident and aligned with said radiation axis whereby in this coincident condition electrical signals representative of received radiation having passed through said moving web to each detector segment are equal and taken together are indicative of a single measurement of said characteristic, but if said signals are unequal this is indicative of a misalignment between said axes, and including processing means for eliminating any error due to misalignment between said axes by processing said signals, one from each said segment, including mathematically processing said signals by use of summing and squaring, to eliminate dependence on misalignment.
Dependencies are inferred from the claim text.