Holmium Oxide Glasses as Calibration Standards for Near Infrared Moisture Sensors

• US 20170059481A1
• Filed: 08/27/2015
• Published: 03/02/2017
• Est. Priority Date: 08/27/2015
• Status: Active Grant

• Current Assignee: Honeywell Limited (Honeywell International Inc.)
• Original Assignee: Honeywell Limited (Honeywell International Inc.)
• Inventors: Tixier, Sebastien
• Granted Patent: US 9,891,164 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01N 2021/3155 Measuring in two spectral ranges, e.g. UV and visible
• CPC Class Codes: G01N 2021/8663 Paper, e.g. gloss, moisture content inspecting the presence of flaws in moving materials, e.g. paper G01N21/89; measurement of gloss in general G01N21/57
• CPC Class Codes: G01N 21/278 Constitution of standards
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3559 in sheets, e.g. in paper
• CPC Class Codes: G01N 33/346 paper sheets

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.

Claims

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 and the second region is selected to detect infrared radiation that is insensitive to water 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.

2. The sensor of claim 1 wherein the one or more calibration standards comprises holmium oxide glass and didymium glass.

3. The sensor of claim 1 wherein each of the one or more calibration standards consists essentially of holmium oxide glass.

4. The sensor of claim 1 comprising a plurality of calibration standards exhibiting different degrees of infrared radiation absorption.

5. The sensor of claim 4 comprising a plurality of calibration standards with different levels of holmium oxide therein.

6. The sensor of claim 4 comprising a plurality of calibration standards having different thicknesses.

7. The sensor of claim 4 wherein the different degrees of infrared radiation absorption correspond to different predetermined levels of moisture absorption.

8. The sensor of claim 4 wherein the plurality of calibration standards comprise a plurality of calibration standards each consisting essentially of holmium oxide glass.

9. The sensor of claim 1 wherein the first region is about 1.94 microns and the second region is about 1.8 microns.

10. The sensor of claim 1 comprising means for constructing a calibration curve from which a correction factor can be obtained and applied to calculate paper web water weight or moisture to generate corrected water weight or moisture.

11. The sensor of claim 1 wherein the sensor operates in the transmission mode with the receiver being configured to detect radiation that has been transmitted through the paper web.

12. The sensor of claim 1 wherein the sensor operates in the reflection mode with the receiver being configured to detect radiation that has been reflected from the paper web.

13. 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 for water and the second region is selected to detect infrared radiation that is insensitive to water 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:

(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.

14. The method of claim 13 wherein the radiation is either transmitted through or reflected from the paper.

15. The method of claim 13 where step (e) comprises standardizing the detector to yield a correction factor to modify detector measurements.

16. The method of claim 13 wherein step (e) comprises standardizing the sensor to yield a correction factor to modify sensor moisture or water weight calculations.

17. The method of claim 13 wherein the first region is about 1.94 microns and the second region is about 1.8 microns.

18. The method of claim 13 comprising repeating steps (b), (c), and (d) a plurality of times using standards exhibiting different degrees of infrared radiation absorption before executing step (e).

19. The method of claim 18 wherein the standards exhibiting different degrees of infrared radiation absorption have different levels of holmium oxide therein.

20. The method of claim 18 wherein the standards exhibiting different degrees of infrared radiation absorption have different thicknesses.