Abstract: A method includes illuminating a mixture of materials in a wet-end of a paper process, where the mixture includes an ultraviolet-activated material. The method also includes measuring light from the mixture and determining a property of the ultraviolet-activated material based on the measured light. The method may further include adjusting an operation in the wet-end of the paper process based on the determined property of the ultraviolet-activated material. The determined property could include a quantity of fluorescent material in recycled material used to form stock for a paper machine and/or a quantity of fluorescent material in stock provided to a headbox in the paper process. Adjusting the operation in the wet-end could include adjusting an amount of one or more materials used to form stock provided to the headbox, such as a fluorescent whitening agent, fixative, fluorescent fiber, fluorescent pigment, fluorescent particle, fluorescent highlight, fluorescent planchette, or fluorescent quencher.

Abstract: A method includes receiving a sheet of material at a sensor assembly. The sensor assembly includes a sensor configured to measure a property of the sheet. The method also includes stabilizing the sheet with respect to the sensor using a guide roller. Stabilizing the sheet includes using the guide roller to remove at least a portion of a first boundary layer of air moving towards the guide roller and to reform at least a portion of a second boundary layer of air moving away from the guide roller. For example, the guide roller could include a plurality of grooves or openings in a surface of the guide roller, or the guide roller could include a plurality of rings spaced apart from one another. Air could move from one side of the guide roller to another side of the guide roller through the grooves, through the openings, or between the rings.

Abstract: A system and method for color measurements or other spectral measurements of a material are provided. An illuminating device generates light for illuminating a sample of material. A detector detects light that has interacted with the sample and provides a measurement of the light that has interacted with the sample. A controller adjusts a duty cycle of the illuminating device to control the illumination of the sample. The measurement could be used by an analyzer to determine a spectral characteristic of the sample (such as a color of the sample). The determination of the spectral characteristic could be done without using any measurement of light that has not interacted with the sample. One or multiple light emitting diodes (LEDs) could be used to illuminate the sample, and the duty cycle of individual LEDs or groups of LEDs could be adjusted.