Sensor and methods for measuring select components in moving sheet products

• US 20060243931A1
• Filed: 04/28/2005
• Published: 11/02/2006
• Est. Priority Date: 04/28/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Beselt, Ronald E., Haran, Frank M.
• Granted Patent: US 7,291,856 B2
• Time in Patent Office: Days
• US Class Current: 250/574
• 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 21/3554 for determining moisture content
• CPC Class Codes: G01N 21/3559 in sheets, e.g. in paper
• CPC Class Codes: G01N 21/86 Investigating moving sheets G01N21/89 takes precedence
• CPC Class Codes: G01N 21/8901 Optical details; Scanning details per se G02B

Abstract

A compact, long lasting sensor for measuring components such as moisture in moving sheets including paper in a papermaking apparatus employs light sources that produce radiation within defined wavelength regions of interest and the light sources are modulated at high frequencies using non-mechanical techniques. A single detector with various radiation sources can measure at all frequencies while keeping information separated. Superluminescent light emitting diode or laser diode light sources can be directly electrically modulates for improved noise rejection. These higher power and bright light sources afford excellent fiber optic launch efficiency and permits the sensor to be scanned at much faster rates over the paper being monitored.

Claims

1. A sensor, for measuring at least one selected component in a composition, that comprises:

at least one light source that generates light having a desired wavelength range to detect a component in the composition wherein the at least one light source is configured to direct the light to the composition;

drive means for modulating the at least one light source, with the proviso that the drive means does not mechanically modulate the at least one light source; and

detection means for receiving light that emerges from the composition.

2. The sensor of claim 1 wherein the at least one light source comprises a superluminescent light-emitting diode or laser diode.

3. The sensor of claim 1 wherein the drive means for modulating the at least one light source directly modulates a drive current of the at least one light source.

4. The sensor of claim 1 wherein the drive means for modulating the at least one light source employs one or more external electro-optical modulators.

5. The sensor of claim 1 wherein the drive means for modulating the at least one light source employs one or more external acousto-optical modulators.

6. The sensor of claim 1 wherein the drive means for modulating at least one light source modulates at a rate of at least 5 kHz.

7. The sensor of claim 1 wherein the at least one light source comprises a light emitting device comprising a superluminescent light-emitting diode or laser diode that is coupled to an optical fiber so that light from the light emitting device is transmitted through the optical fiber.

8. The sensor of claim 7 comprising an optical device that is coupled to the optical fiber and that is configured to direct light to the composition.

9. The sensor of claim 8 wherein the optical device is configured to receive light that emerges from the composition.

10. The sensor of claim 1 wherein the detection means for receiving light generates signals that are proportional to the intensity of light received and wherein the sensor further comprises means for filtering noise from the signals.

11. The sensor of claim 10 wherein the means for filtering noise comprises lockin amplifiers that amplifies the modulated signal and converts the modulated signal to a proportionate DC level signal while simultaneously suppressing the noise with a low-pass filter.

12. The sensor of claim 11 wherein the lockin amplifiers remove background noise.

13. The sensor of claim 1 wherein filtering the light with an optical filter is not needed to generate the light having the desired wavelength range.

14. A sensor, for measuring at least one selected component in a composition, that comprises:

a first light source that generates a first light having a first wavelength region that is sensitive to the component;

a first drive means for modulating the first light source, with the proviso that the first drive means does not mechanically modulate the first light source;

a second light source that generates a second light having a second wavelength region that has a different sensitivity to the component; and

a second drive means for modulating the second light source, with the proviso that the second drive means does not mechanically modulate the second light source.

15. The sensor of claim 14 wherein the first drive means for modulating the first light source modulates the first light source at a first frequency to generate a first modulated light signal and the second drive means for modulating the second light source modulates the second light source at a second frequency to generate a second modulated light signal, wherein the first frequency is different from the second frequency.

16. The sensor of claim 15 wherein the first modulated light signal is multiplexed with the second modulated light signal for transmission through an optical fiber.

17. The sensor of claim 16 wherein frequency division multiplexing is employed to multiplexed the first and second modulated light signals.

18. The sensor of claim 15 wherein the detection means for receiving light comprises a single detector and a single pre-amplifier that detects light having the first frequency and the second frequency.

19. The sensor of claim 14 wherein (i) the first light source comprises a first light emitting device comprising a superluminescent light-emitting diode or laser diode that is coupled to an optical fiber so that light from the first light emitting device is transmitted through the optical fiber and (ii) the second light source comprises a second light emitting device comprising a superluminescent light-emitting diode or laser diode that is coupled to an optical fiber so that light from the second light emitting device is transmitted through the optical fiber.

20. An apparatus, for measuring at least one selected component in a composition, that comprises:

at least one light source that generates light having a desired wavelength range to detect a component in the composition wherein the at least one light source is configured to be delivered to a plurality of positions on the composition;

drive means for modulating the at least one light source, with the proviso that the drive means does not mechanically modulate the at least one light source; and

a plurality of detection means for receiving light that emerges from the composition at the plurality of positions.

21. The apparatus of claim 20 comprising:

a first light source that generates a first light having a first wavelength region that is sensitive to the component;

a first drive means for modulating the first light source, with the proviso that the first drive means does not mechanically modulate the first light source;

a second light source that generates a second light having a second wavelength region that has a different sensitivity to the component; and

a second drive means for modulating the second light source, with the proviso that the second drive means does not mechanically modulate the second light source.

22. The apparatus of claim 21 wherein the first drive means for modulating the first light source modulates the first light source at a first frequency to generate a first modulated light signal and the second drive means for modulating the second light source modulates the second light source at a second frequency to generate a second modulated light signal, wherein the first frequency is different from the second frequency.

23. The apparatus of claim 22 wherein the first modulated light signal is multiplexed with the second modulated light signal for transmission through an optical fiber.

24. The apparatus of claim 23 wherein frequency division multiplexing is employed to multiplexed the first and second modulated light signals.

25. A method for sensing a substance in a composition that comprises the steps of:

(a) irradiating the composition with radiation including wavelengths in at least first and second separate wavelength regions wherein the radiation is provided by light sources that are modulating non-mechanically, wherein radiation in the first wavelength region is strongly sensitive to the substance in the composition and radiation in the second wavelength region is less sensitive to the substance in the composition;

(b) detecting the amount of radiation that emerges from the composition in the first and second separate wavelength regions.

26. The method of claim 25 wherein step (a) comprises irradiating the composition with a first modulated light signal that is modulated at a first frequency and second modulated light signal that is modulated at a second frequency which is different from the first frequency.

27. The method of claim 26 wherein the first modulated light signal is multiplexed with the second modulated light signal for transmission through an optical fiber and directed toward the composition.

28. The method of claim 27 wherein frequency division multiplexing is employed to multiplexed the first and second modulated light signals.

29. The method of claim 25 further comprising the step of computing the amount of substance in the composition based upon the detected amount of radiation in the first and second wavelength regions.

30. The method of claim 25 wherein the composition is a flat sheet product that comprises paper or plastic.

31. The method of claim 25 wherein the level of water in the paper is computed.