WO1999066316A1 - Mesure de l'humidite par absorption de micro-ondes - Google Patents

Mesure de l'humidite par absorption de micro-ondes Download PDF

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Publication number
WO1999066316A1
WO1999066316A1 PCT/EP1999/003962 EP9903962W WO9966316A1 WO 1999066316 A1 WO1999066316 A1 WO 1999066316A1 EP 9903962 W EP9903962 W EP 9903962W WO 9966316 A1 WO9966316 A1 WO 9966316A1
Authority
WO
WIPO (PCT)
Prior art keywords
measuring
microwave
microwaves
measured
moisture content
Prior art date
Application number
PCT/EP1999/003962
Other languages
German (de)
English (en)
Inventor
Josef Reitner
Alfred Weingartner
Original Assignee
Mahlo Gmbh & Co. Kg
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE19835859A external-priority patent/DE19835859C2/de
Application filed by Mahlo Gmbh & Co. Kg filed Critical Mahlo Gmbh & Co. Kg
Priority to EP99927924A priority Critical patent/EP1088219A1/fr
Publication of WO1999066316A1 publication Critical patent/WO1999066316A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N22/00—Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more
    • G01N22/04—Investigating moisture content

Definitions

  • the invention relates to a method and a device for measuring the moisture content of a flat sample by microwave absorption, in particular the measurement of the residual moisture content of a continuously conveyed web, the microwaves shining through the sample several times along a measuring beam chain with at least two measuring beams and the field strength of Microwaves after
  • the material to be measured consists, for example, of paper, coated paper, cardboard, tissue, plastic, textile material and / or the like.
  • a generic method and a generic device are known from EP 0 009 187 AI.
  • the known device has a microwave oscillator which is connected to a first horn by a microwave waveguide
  • Ab radiation from microwaves is connected to a measuring section.
  • the microwaves emitted by the first microwave radiation strike the material to be measured.
  • the field strength of the microwaves is weakened by absorption in the sample.
  • the field strength of the microwaves propagating in the direction of the measuring section is weakened by reflection, in particular on the surface of the measured material, and by diffraction or scattering. The microwaves consequently reach a microwave receiver at the end of the measuring path when the reception power is lower than the transmission power.
  • the microwaves become a second via a second microwave waveguide Microwave emitter directed, which emits the microwaves on a second measuring section, in the course of which the microwaves in turn cross the material to be measured.
  • the previously known device has a measuring chain with a total of four successive measuring sections.
  • the microwaves are detected by a measuring detector, which transmits a signal corresponding to the remaining field strength to an evaluation device.
  • the detector signal consists of an electrical voltage that is compared with a reference voltage.
  • the reference voltage represents the measurement signal in the case in which no material to be measured is arranged in the device.
  • the multiple radiation of the measured material increases the sensitivity, so that, for example, measured material with a residual moisture content of 1 g water / m - .30 g water / m can be measured. It is known in particular in the manufacture of textiles
  • the microwaves are modulated with a modulation frequency of 100 Hz and a stroke of more than 25%, so that fluttering movements of the measured material, which typically occur with lower frequencies than the modulation frequency in the direction of the measuring section, have no influence on the measurement result.
  • microwaves can be reflected and scattered on the material to be measured from one of the measuring sections into the microwave receiver of another. Arrive at the measuring section, so that Measurement result is falsified. This is particularly the case with a special embodiment of the previously known device, in which the microwaves radiate the measured material alternately in the course of the measuring chain from one side of the measured material to the opposite side of the measured material and vice versa. Furthermore, it is also possible that microwaves from the
  • Microwave emitters of a measuring section can be passed directly or by deflection in another way than on the measured material into one or more microwave receivers of another measuring section.
  • the object of the present invention is to provide a method and a device of the type mentioned at the outset, in which the microwave signal present after passing through the last heating section or the last measuring beam largely depends only on the absorption in the material to be measured.
  • This task is accomplished through a process with the
  • the microwaves are at least the microwave chain linearly polarized along two of the measuring beams, wherein the polarization directions of the two measuring beams differ from one another, preferably an angle of about 90 ° with one another.
  • Device side are for this purpose each to one-other opposite End points of two measuring sections, on each of which one of the measuring beams lies, a coordinated one
  • Microwave emitter / microwave receiver pair arranged.
  • the microwave receiver of the first pair is via a row conductor and possibly one or several further measuring sections are coupled to the microwave transmitter of the second pair.
  • the microwave emitter of the first pair (first microwave emitter) and the microwave emitter of the second pair (second microwave emitter) are coupled to the microwave transmitter of the second pair.
  • Microwave emitters designed and aligned in such a way that linearly polarized microwaves can be transmitted on the respective measuring section, the polarization direction of the microwaves to be emitted by the first microwave emitter and that by the second microwave emitter being different.
  • Measuring beams are understood to mean the paths of propagation of the microwaves on which they traverse the material to be measured in the course of the measuring chain.
  • the measuring beams can have a finite width transverse to the direction of propagation.
  • the microwaves transmitted on the measuring sections or spreading along the measuring beams each have a property by means of which they can be selected from one another. If there are scattering, diffraction and / or reflection processes that do not depend on the absorption of the measured material,. it can be avoided that at the end of one of the at least two measuring beams, microwave signals other than those of the associated measuring section are received, forwarded and / or detected.
  • a sum microwave signal which may be present at the end of a measuring section and which contains a first, linearly polarized component and a second, linearly polarized component in another polarization direction and / or unpolarized component is broken down using the polarization property, both components being evaluated.
  • the undesired second component is used in particular to determine one caused by the respective material to be measured to determine the reflected, diffracted and / or scattered portion of the microwave radiation propagating along the measuring beam chain in order not to wrongly attribute this portion to the absorption of the microwave radiation in the material to be measured, which would lead to an overestimation of the moisture content.
  • the measuring accuracy is increased, in particular in the case of method variants, in which, to determine the moisture content from the field strength of the microwaves after passing through the last measuring beam, a reference value is used as a comparison value which corresponds to the measuring arrangement in the absence of a measured material.
  • the measuring beams with the linearly polarized microwaves preferably traverse the planar measured material at an angle of 30 ° to 90 °, preferably approximately 60 °, against the surface thereof.
  • An advantage of a non-perpendicular irradiation of the material to be measured is that reflections on the surface of the material to be measured are not reflected directly back into the microwave emitter of the respective measuring section. Standing waves can thus be avoided.
  • the measuring beams traverse the material to be measured at locations spaced apart from one another and in which the directions of polarization of two measuring beams that are adjacent to each other are different. In particular, two variants are proposed for this.
  • the points at which the measuring beams cross the material to be measured are approximately in a straight line to one another.
  • the locations are approximately at the corners of a polygon, in particular a square.
  • the measurement beams preferably have different polarization directions at adjacent corners of the square. The latter case is particularly preferred if the polarization directions of the measuring beams each have two mutually adjacent corners form an angle of approximately 90 °. This has the advantage that the microwaves propagating along the two adjacent measuring beams can be selected on the basis of their polarization directions.
  • the distance between the measuring beams at diagonally opposite corners of the square is preferably chosen to be such that at most a negligibly small extent, portions of the microwaves propagating along these measuring beams with the same polarization direction can reach the end of the other measuring section.
  • the temperature of the measured material is preferably measured without contact and the measured temperature value is taken into account when determining the moisture content.
  • a thermopile, a pyroelectric sensor or a bolometer are preferably used for this.
  • FIG. 1 shows a first embodiment of the device according to the invention in a schematic side view
  • Fig. 2 is a diagram of the radiation directions and the associated directions of polarization of microwaves in that shown in Fig. 1
  • Fig. 3 is a schematic front view of a second embodiment 's of the inventive device.
  • Fig. 4 shows a section through device parts located on the back of the device shown in Fig. 3, seen from the front.
  • FIG. 1 shows a material web 1 which, for example, has paper, coated paper, cardboard material, plastic, textile material and / or the like sheet material, and which in the illustration shown is conveyed continuously in the direction into the image plane.
  • the web of example has a surface density of 3000-5000 g / m and comprises a to be measured "moisture content.
  • the web 1 is passed through a frame-like support 10, are attached to the parts of the measuring device.
  • the measuring device has an oscillator 9 which generates microwaves, for example with a frequency of 8-12 GHz or with a frequency of 2-4 GHz, during operation of the device
  • the microwaves are coupled into the waveguide 8a and connected to a first horn radiator 4a the front 2 of the web 1.
  • the first Horn radiator 4a transmits the microwaves to a transmission path along a measuring beam 4, which ends at a first horn receiver 4b at the rear 3 of the web 1, where the microwaves are coupled into and on a second waveguide 8b
  • a detector 11 which detects the field strength of the microwaves and emits a detection signal to the computer 12, in which the temperature of the material web is determined from the detection signal and possibly other signals, such as a temperature value measured without contact 1 represents, the moisture content of the web 1 at the current conveying position on the carrier 10 is determined.
  • the waveguides 8a, 8b, 8c, 8d, 8e other types of microwave conductors, for example strip conductors and / or coaxial cables, can also be used.
  • the microwaves coupled into the waveguide 8a are preferably at a frequency of 70 Hz with a frequency swing of 2 to 4 GHz modulated (wobbled).
  • Interfering signals, for example from standing waves, with frequencies greater than or equal to 70 Hz, are eliminated in particular by a low-pass circuit, not shown, between the detection device 11 and the computer 12.
  • the detection device 11 which is preferably broadband and detects in the entire transmission frequency range and has a low-pass filter connected downstream, forms an average over the transmission frequency range, which is largely free of undesired effects at certain frequencies of the
  • the detection device 11 has, for example, a Schottky diode for receiving the microwaves.
  • the directions of radiation of the microwaves and the respective directions of polarization on the measuring beams 4, 5, 6, 7 are shown schematically.
  • the double arrow in the upper part of FIG. 2 shows the direction in which the web 1 is conveyed.
  • the microwaves cross the web 1 from top to bottom, ie from the Front 2, on which the first waveguide 8a lies, to the rear 3, on which the second waveguide 8b lies.
  • the microwaves are linear along the measuring beam 4, polarized in the conveying direction of the web 1.
  • the microwaves traverse the web 1 from bottom to top, being polarized linearly, at an angle of 90 ° transversely to the conveying direction of the web 1.
  • the crossing directions and the polarization directions along the measuring beams 6, 7 correspond to the crossing directions and the polarization directions along the measuring beams 4, 5.
  • the polarization directions of mutually adjacent measuring beams 4, 5, 6, 7 are different, so that reflected, diffracted and / or scattered portions of neighboring microwaves
  • Measuring beams at the respective microwave receiver 4b, 5b, 6b, 7b of a measuring section can be selected.
  • the respective horn receivers 4b, 5b, 6b, 7b are set to the respective polarization direction of the transmission path and are insensitive to microwave radiation which has a polarization direction rotated by 90 °.
  • horns widening in the manner of a funnel are provided, the cross-section of which, as cannot be seen from FIG. 1, is rectangular and is oriented in accordance with the respective polarization direction of the measuring section.
  • the direction of polarization coincides with the orientation of the narrower side of the cross-sectional rectangle.
  • patch antennas or rectangular conductor tracks are used, or other means known to the person skilled in the art for transmitting microwaves in a specific polarization direction.
  • the microwaves are linearly polarized along the middle two of the four measuring beams. Nevertheless, any undesirably deflected microwaves from adjacent measuring sections can be effectively selected.
  • Fig. 3 and Fig. 4 show another measuring arrangement with horns 14a, 15a, 16a, 17a and with horn receivers 14b, 15b, 16b, 17b, which are arranged at end points of four measuring sections, each in pairs opposite to each other on a conveyor section of the web 1 are.
  • Fig. 3 shows the arrangement on the front, Fig. 4 on the back of the web 1, each seen from the front.
  • the microwaves are coupled into the first horn antenna 14a via a microwave conductor, in particular a coaxial cable.
  • a microwave conductor in particular a coaxial cable.
  • the first horn radiator 14a is equipped with a horn 18 which has a rectangular cross section which widens in the manner of a funnel in the direction of the measuring section, the longer side of the rectangle in FIG.
  • the horn radiator 14a emits microwaves with this polarization direction onto the measuring section.
  • the microwaves are received by a horn receiver 14b with a horn 18 oriented in the same direction. Both on the front and the horns are on the back of the web '18 arranged and oriented such that the total of four measuring paths pass through the web 1 at locations that define approximately the corners of a square.
  • Horn receivers 14b now guide the microwaves via a microwave guide to the horn radiator 15a, which lies at one end of the measuring section that of the first Measuring section is diagonally opposite.
  • the horn 15a and the associated horn receiver 15b have the same orientation as the horn 14a and the horn receiver 14b, ie the microwaves on the two associated measuring sections are linearly polarized in the same direction.
  • Direction of polarization along measuring beams immediately following one another in the measuring beam chain first irradiating the measured material in one direction and then immediately irradiating the measured material in the opposite direction, direction-dependent effects such as those described above can be compensated or a suitable mean value can be formed.
  • the field strength of the microwaves is only weakened by a small percentage when the sample is irradiated, it is irrelevant in which direction the sample is first irradiated.
  • the microwaves on the front of the web 1 are directed from the horn receiver 15b via a microwave guide to the horn radiator 16a, which emits the microwaves on the third measuring path to the horn receiver 16b.
  • the microwaves are then passed to the fourth and last measuring section, at the end points of which the horn radiator 17a and the horn receiver 17b are arranged, via a further microwave guide on the back of the web 1.
  • the direction of polarization with respect to the horn radiators 14a, 15a and horn receivers 14b, 15b of the first and second measuring sections, the horn radiators 16a, 17a and the horn receivers 16b, 17b of the third and fourth measuring sections are again the same
  • the third and fourth measuring sections cross the web 1 again at diagonally opposite corner points of the imaginary square.
  • the microwaves are emitted by the horn receiver 17b
  • the detection signal is evaluated in particular in the same way as in the device shown in FIG. 1.
  • the device of Figs. 3 and 4 has the advantage that the measuring arrangement has a smaller width, i.e. the same distance between the next adjacent measuring sections. Material webs with a smaller width can be measured. Furthermore, the spatial averaging of the moisture content over areas of smaller width is possible, whereby the same distances between the next adjacent measuring sections can be maintained.
  • Microwaves radiated through the measuring material via a chain of measuring sections with a total of four successive measuring sections is not limited to a measuring section chain with four chain links (measuring sections). Rather, the measuring section chain can have any number greater than or equal to two measuring sections. The number depends in particular on the desired sensitivity. Reference list

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention concerne un procédé et un dispositif pour mesurer la teneur en humidité d'un objet à mesurer (1) plat par absorption de micro-ondes. Les micro-ondes irradient plusieurs fois l'objet à mesurer (1) le long d'une chaîne d'émission de faisceaux de mesure comportant au moins deux faisceaux de mesure (4, 5, 6, 7). Après le passage du dernier faisceau de mesure (7), les micro-ondes sont acheminées à un système de détection (11) par lequel l'intensité de champ des micro-ondes est détectée. La teneur en humidité est déterminée à partir de cette intensité de champ. L'invention vise à permettre la détermination la plus précise possible de la teneur en humidité. A cet effet, les micro-ondes sont polarisées linéairement au moins le long de deux des faisceaux de mesure (4, 5, 6, 7), les sens de polarisation des deux faisceaux de mesure se différenciant l'un de l'autre. Il est ainsi possible de reconnaître et d'éliminer, dans chaque récepteur à l'extrémité des deux faisceaux de mesure, des composantes hyperfréquence, éventuellement déviées, d'autres faisceaux de mesure, au moyen de l'état de polarisation.
PCT/EP1999/003962 1998-06-18 1999-06-09 Mesure de l'humidite par absorption de micro-ondes WO1999066316A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP99927924A EP1088219A1 (fr) 1998-06-18 1999-06-09 Mesure de l'humidite par absorption de micro-ondes

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE19827241 1998-06-18
DE19827241.3 1998-06-18
DE19835859.8 1998-08-07
DE19835859A DE19835859C2 (de) 1998-06-18 1998-08-07 Feuchtemessung durch Mikrowellenabsorption

Publications (1)

Publication Number Publication Date
WO1999066316A1 true WO1999066316A1 (fr) 1999-12-23

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Application Number Title Priority Date Filing Date
PCT/EP1999/003962 WO1999066316A1 (fr) 1998-06-18 1999-06-09 Mesure de l'humidite par absorption de micro-ondes

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EP (1) EP1088219A1 (fr)
WO (1) WO1999066316A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2629701C1 (ru) * 2016-04-06 2017-08-31 Федеральное государственное учреждение науки Институт проблем управления им. В.А. Трапезникова Российской академии наук Устройство для измерения влагосодержания жидкости

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0009187A1 (fr) * 1978-09-16 1980-04-02 Hoechst Aktiengesellschaft Procédé et dispositif de mesure de l'humidité d'échantillons plats par absorption de microondes
GB2112148A (en) * 1981-12-23 1983-07-13 Sentrol Systems Ltd Microwave moisture sensor

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0009187A1 (fr) * 1978-09-16 1980-04-02 Hoechst Aktiengesellschaft Procédé et dispositif de mesure de l'humidité d'échantillons plats par absorption de microondes
GB2112148A (en) * 1981-12-23 1983-07-13 Sentrol Systems Ltd Microwave moisture sensor

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EP1088219A1 (fr) 2001-04-04

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