Holmium oxide glasses as calibration standards for near infrared moisture sensors
First Claim
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1. A paper web moisture sensor comprising:
- an infrared radiation source disposed to direct a beam of infrared radiation into the web;
a radiation receiver disposed to detect at least a portion of a beam of radiation emerging from the web, the receiver configured to detect the amount of radiation in first and second separate wavelength regions of the radiation spectrum wherein the first region is positioned around the infrared absorption peak for water, which is about 1.94 microns, and the second region is selected to detect infrared radiation that is insensitive to water, which is about 1.8 microns, and to generate first and second signals therefrom;
computer means operatively coupled to the receiver for computing the amount of water in the web based on the first and second signals; and
one or more calibration standards with each standard comprising holmium oxide glass wherein each standard is maneuverable to a calibration position to receive a beam of infrared radiation from the infrared radiation source and to direct a beam of radiation emerging from the standard to the receiver which measures the radiation in the first wavelength region and the radiation in the second wavelength region to standardize the sensor.
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Abstract
Near infrared moisture sensors using stable holmium oxide glass calibration standards that simulate different moistures levels in paper obviates problems associated with glass encased paper samples. Holmium oxide glass has a strong absorption at 1.93 microns which is close to absorption by paper. Standards can have varying thicknesses to simulate different moisture levels. Didymium glass can also be used with holmium oxide glass. The moisture sensor operates at reference and measurement infrared regions of 1.94 microns and 1.8 microns, respectively.
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18 Claims
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1. A paper web moisture sensor comprising:
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an infrared radiation source disposed to direct a beam of infrared radiation into the web; a radiation receiver disposed to detect at least a portion of a beam of radiation emerging from the web, the receiver configured to detect the amount of radiation in first and second separate wavelength regions of the radiation spectrum wherein the first region is positioned around the infrared absorption peak for water, which is about 1.94 microns, and the second region is selected to detect infrared radiation that is insensitive to water, which is about 1.8 microns, and to generate first and second signals therefrom; computer means operatively coupled to the receiver for computing the amount of water in the web based on the first and second signals; and one or more calibration standards with each standard comprising holmium oxide glass wherein each standard is maneuverable to a calibration position to receive a beam of infrared radiation from the infrared radiation source and to direct a beam of radiation emerging from the standard to the receiver which measures the radiation in the first wavelength region and the radiation in the second wavelength region to standardize the sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of standardizing a sensor that measures moisture in paper having an infrared radiation source and radiation detector with a gap therebetween for directing infrared radiation along a radiation path into the paper and detecting the amount of radiation emerging from the paper, the detector being configured to detect the amount of radiation in first and second separate wavelength regions of the radiation spectrum wherein the first region is positioned around the infrared absorption peak forwater, which is about 1.94 microns, and the second region is selected to detect infrared radiation that is insensitive to water, which is about 1.8 microns, and to generate first and second signals therefrom and means operatively coupled to the detector for computing the amount of water in the paper based on the first and second signals, said method comprising:
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(a) employing a standard that simulates a predetermined moisture level wherein the standard comprises holmium oxide glass; (b) positioning the standard into the radiation path; (c) measuring the radiation in the first wavelength region that emerges from the paper; (d) measuring the radiation in the second wavelength region that emerges from the paper; and (e) standardizing the detector and/or sensor. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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Specification