EP0137696A2
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Method and apparatus for measuring water content
Assignee: Wiggins Teape Group Ltd
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Filing: 1984-08-29
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Granted: —
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Expires: 2004-08-29
Abstract
Abstract A modified infra-red scanning gauge used in measuring the moisture content of a paper-web during manufacture or when subject to a coating practice, has a measurement channel (216) and a reference channel (218). The measurement channel is based on the infra-red absorption spectrum of water which has an absorption band centred on 1.94 microns. The reference channel is conventionally at a wavelength of 1.83 microns (Figure 2A) where water has previously been considered to be transparent to infra-red or at a wavelength of 1.68 microns. The gauge is intended for measurement of high water content, where at 1.94 microns absorption effectively becomes total thereby preventing measurements being made, and uses a narrow-band filter (222'A) of 0.03 micron wavelength offset from the peak of the 1.94 micron absorption band in the range 1.76 to 1.87 microns, previously considered stable as regards water content but now disclosed as showing a water-dependent variation at high water contents, In a specific example a 1.83 micron filter (222A) is used for the measurement channel (218) and a 1.68 micron filter (224A) for the reference channel (218). The modified gauge which may be of the transmission or scatter type has particular use at the wet end of a paper-making machine (Figure 1).
Inventors
- 👤 Neil Francis Campbell
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 05:42
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/17; G01N21/25; G01N21/31; G01N21/35; G01N21/3554; G01N21/3559; Y; Y10; Y10S; Y10S162/00; Y10S162/06
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
206 words
Apparatus for measuring the water content of a material over a predetermined range and having a source of infra-red radiation for directing at the material, detector means for such radiation and at least first and second filters for selecting radiation for detection at a first wavelength band at which the detected radiation is affected by water content and a second wavelength band at which the detected radiation is substantially unaffected by water content respectively, whereby first and second signals are produced in dependence upon the radiation detected at said first and second wavelength bands respectively, and means responsive to said first and second signals to derive a signal having a value representing the water content, characterised in that said first filter has a significant response at a wavelength offset fran the peak of the absorption band so that the absorption detected at the first wavelength band is substantially attenuated with respect to the absorption at the peak, and in that said second filter has a response at a wavelength removed from said first wavelength band and substantially independent of water content over the predetermined range. 2. Apparatus as claimed in Claim 1 in which said first wavelength band lies in the range of 1.76 to 1.87µm.
Claim 2
Dependent Claim
15 words
Apparatus as claimed in Claim 2 in which said first filter is a narrow-band filter.
Claim 3
Dependent Claim
17 words
Apparatus as claimed in Claim 3 in which said first filter has a bandwidth of 0.03 pn.
Claim 4
Dependent Claim
23 words
Apparatus as claimed in any one of Claims 1 to 4 in which said second filter has a response at about 1.7 µm.
Claim 5
Dependent Claim
101 words
In a paper-making machine comprising in succession a Foudrinier wire on which the web is formed; a press section for removing water from the web; and a dryer section for drying the web to a relatively low moisture content:- apparatus as claimed in any one of Claims 1 to 5 in which the infra-red source, filters and the detectors arrangement is arranged in a transmission type or scatter type gauge positioned to one side or on both sides respectively of the web, and wherein the gauge is mounted adjacent the web at a location preceding the outlet end of said dryer-section.
Claim 6
Dependent Claim
88 words
In a paper-making machine including a coater followed by a dryer section or in a coating machine having a coater followed by a dryer section :- apparatus as claimed in any one of Claims 1 to 5 in which the infra-red source, filters and the detector arrangement is arranged in a transmission type or scatter type gauge positioned to one side or.on both sides respectively of the web, and wherein the gauge is mounted adjacent the web at a location preceding the outlet end of said dryer section.
Claim 7
Independent Claim
153 words
A method of measuring the water content of a material using the absorption spectrum of the material, including moisture therein, in the infra-red where the spectrum includes an essentially water-dependent absorption band, and in which method infra-red radiation is directed onto the material and selective detection is performed at a measurement wavelength band and a reference wavelength band, and the absorption (or transmissivity) of the material at the measurement wavelength band is expressed by the radiation detected at the measurement wavelength band referred to that detected at the reference wavelength band, wherein said measurement wavelength band has a significant portion thereof offset from the peak absorption wavelength of said water-dependent absorption band such that absorption at the measurement wavelength band is substantially attenuated with respect to that at the peak wavelength; and said reference wavelength band is remote from said measurement wavelength band and is substantially unaffected by the moisture in the material.
Claim 8
Independent Claim
153 words
A method of measuring the water content of a material using the absorption spectrum of the material, including moisture therein, in the infra-red where the spectrum includes an essentially water-dependent absorption band, and in which method infra-red radiation is directed onto the material and selective detection is performed at a measurement wavelength band and a reference wavelength band, and the absorption (or transmissivity) of the material at the measurement wavelength band is expressed by the radiation detected at the measurement wavelength band referred to that detected at the reference wavelength band, wherein said measurement wavelength band has a significant portion thereof offset from the peak absorption wavelength of said water-dependent absorption band such that absorption at the measurement wavelength band is substantially attenuated with respect to that at the peak wavelength; and said reference wavelength band is remote from said measurement wavelength band and is substantially unaffected by the moisture in the material.
Claim 9
Dependent Claim
21 words
A method as claimed in Claim 8 in which said measurement wavelength band lies in the range 1.76 to 1.87 µm.
Claim 10
Dependent Claim
19 words
A method as claimed in Claim 9 in which said measurement wavelength band is defined by a narrow-band filter.
Claim 11
Dependent Claim
17 words
A method as claimed in Claim 10 in which said filter has a bandwidth of 0.03 µm.
Claim 12
Independent Claim
22 words
A method as claimed in any one of Claims 8 to 11, in which said reference wavelength band is about 1.7 µm.
Claim 13
Dependent Claim
73 words
In a paper-making machine comprising in succession a Foudrinier wire on which the web is formed; a press section for removing water from the web and a dryer section for drying the web to a relatively low moisture content: a method of on-line measurement of the water content of the web at a location preceding the outlet of the dryer section which is in accord with any one of Claims 8 to 12.
Claim 14
Dependent Claim
60 words
In a paper-making machine including a coater followed by a dryer section or in a paper coating machine having a coater followed by a dryer section: a method of on-line measurement of the water content of the web at a location preceding the outlet of the dryer section which is in accord with any one of Claims 8 to 12.
References Cited (Backward Citations)
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