DE2318032A1 - INFRARED MEASUREMENT ARRANGEMENT - Google Patents

Description

Patent attorneys Dipl.-Ing. F Ψκιοκμανν,

Dipl, -Tng. H. ^ 'EickmaNN, D1PL.-PHYS. Dr. K. Fincke Dipl.-Ing. F. A. Weιckmann, Dipl.-Chem. B. Huber

8 MONKS 86, DEN JkJThI ' POST BOX 8608 * 0

MÖHLSTRASSE 22, CALL NUMBER 98 39 21/22

Ref. 9-GY

INPRA SYSTEMS, INCORPORATED, 650 Ackerman Road, Columbus,

Ohio 43202, USA

Infrared measurement

The invention relates to an arrangement for measuring a material property.

The absorption spectrum of a substance is the value curve that shows the percentage absorption of light in the material indicates. The wavelength of the absorbed light corresponds to a certain characteristic property of the substance. The absorption is based on the logarithm of the inverse of the radiation characteristic of the substance, while the spectrogram of the radiation characteristic is often called Absorption spectrum is referred to. Absorption spectra can be used to analyze unknown compositions by using the full spectrum and performing measurements based on it, or else, which is more common by taking more direct measurements of the light transmission properties of the absorption spectrum with

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selected wavelengths showing characteristic absorptions be performed.

From the patent 3,228,282 (Barker) an infrared measuring arrangement is known, with the aid of which the moisture content of paper can be measured, whereby a two-channel system should switch off the effect of a changing basis weight. In this Arrangement, a signal is generated in one channel, which is determined by the weight per unit area of the paper web due to the absorption of molecular bonds a beam of energy through the cellulose molecules depends on the paper web. In the other channel a signal is generated, which both from the basis weight of the paper web as well as their moisture content due to the molecular bond absorption of a second beam of energy by cellulose molecules and water molecules of the paper web depends. The signals of both channels are combined and lead to a result signal, that only depends on the moisture content of the paper web. This result is apparently based on the fact that the second channel to the same extent and in the same way as the first channel, i.e. by molecular bond absorption of the cellulose molecules depends on the sheet weight. Only under this condition can signals be combined with one another in such a way that a dependency on the basis weight of the belt is switched off for all values of the basis weight.

In an improved patent number 3,405,268 (Brunton) of the above a three-channel system is described. A radiant energy source 'radiates energy in the Infrared spectral band. An optical device wins out substantially equal to the infrared spectral band emitted by the radiant energy source at least three separate beams monochromatic radiation and guides each of these rays

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len through a paper tape. Each of the rays has a specific wavelength. The wavelength X _{1 of} a first beam is chosen so that it is influenced by the molecular bond absorption of water molecules in the paper tape, but is independent of the molecular bond absorption by cellulose molecules in the paper tape. The wavelength% p of a second beam is independent of the molecular bond absorption of the cellulose molecules and the water molecules, and the wavelength χ ~ of a third beam is chosen so that it is influenced by the molecular bond absorption of the cellulose molecules, but that it is independent of the molecular bond absorption of the water molecules. On the side of the paper tape opposite the radiant energy source, a detector is arranged _{which collects the radiant energy of each of the beams with the wavelengths X ^, X 2} ^ M ^ 3 after passing through the paper tape and generates separate electrical voltage signals > those of the intensity of the radiant energy of each are proportional to the rays captured. A ratio calculator is used to generate a proportional signal.

en

In a widely known arrangement, in addition to the basis weight the scattering effect is taken into account when determining the moisture content. In this arrangement will the parameters are measured by a first beam and the constituent is measured by a second beam; a third ray will absorbed in neither case. Mathematical tricks are supposed to switch off the scattering effect with each beam.

Other known arrangements use systems with more than two beams to measure specific parameters or components and apply the Lambert-Beer equation to analyze the desired information.

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However, one material contains different substances next to each other each with complicated absorption spectra, the material spectrum is the sum of the individual absorption spectra of the components. In the past, the usual method was infrared spectral analysis of the absorption spectrum of an unknown, multicomponent material in the percentage absorption measurement a number of selected wavelengths, the number being at least equal to the number of components of the material and in the solution of an equal number of simultaneous linear equations of the percentage absorption.

Other known systems are specifically tailored to measure a single property. A signal is selected in such a way that that it is absorbed according to the property to be measured. As is well known, the basis for this is the Absorption wavelength. However, as is further known, the selected wavelengths are not completely selective; she quite overlap and on other properties of the Signals based on materials lead to interference. In order to rule out this undesirable signal behavior, an only opens the interference properties alone responding "reference" signal used. This reference signal is then used in a mathematical calculation process, for example according to Lambert-Beer, a Wheatstone 'see bridge, a ratio calculator, etc. processed and calculates a measurement result of the desired property.

The above-mentioned arrangements of infrared-selective measuring systems, infrared spectrometers and the like can generally control the absorption depending on a wavelength information with one sufficient to identify the correct reference wavelengths Specify accuracy.

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However, the absorption spectrum for the particular material being measured does not always correctly relate to the actual ones Measurements. In various applications it has been found that measurement errors are also based on the "paper quality" can. The spread of the measurements for what is known to be the same Material exhibiting properties, e.g. paper webs with ambient humidity, can possibly affect the paper web orientation to be led back.

It has been found that the use of more than one reference and / or absorption wavelength, i.e. the use of multiple reference and / or multiple absorption wavelengthsj the "paper quality" effects, as they are with simpler single reference and single absorbance measurements occurred, decreased and often turned off.

The invention now has the task of avoiding the above disadvantages. In particular, it is intended to measure material components without being affected by the effects of "grade", ash content and material orientation will. Furthermore, an infrared moisture measuring arrangement is to be created which can detect the weight per unit area and can correct. The infrared sensing arrangement is also intended to be a constituent part of a material such as the weight of cellulosic fiber can measure without errors due to ash changes.

The invention solves this problem by means of an infrared radiation source and an arranged in front of the infrared radiation source, Beam splitter splitting the infrared radiation into at least three separate beams, at least one of the beams a wavelength that can be absorbed according to the material property and the other rays to other properties of the material have related wavelengths, through a detector,

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which detects at least a portion of the radiation not absorbed by the material of each of the beams, through one to the detector connected summation amplifier, which sums the signals of the detected other beams of radiation, through a Ratio circuit showing the ratio of the detected signal of the absorption beam of radiation and the summation signal the summation circuit and by a display device for displaying the ratio signal of the ratio circuit, wherein the ratio signal indicates the material property free from deviations due to other properties of the material indicates. The present invention thus enables a frequency-selective infrared measuring arrangement with the aid of which a basic property of a material, e.g. its moisture content, can be measured. The method used here and the arrangement based on it include an infrared source and a filter for three wavelength bands arranged between the infrared source and the material to be examined a. On the same side of the material to be examined a detector is arranged as that of the material reflected (backscattered) radiation detected. It can also be arranged and detected on the opposite side then the radiation passing through. In a preferred embodiment, the central wavelength is used as the absorption or reference wavelength, while the shorter and longer wavelengths can be used as reference or absorption wavelengths. TJm the To eliminate errors caused by environmental effects, the absorption signal or the sum of the absorption signals is replaced by the reference signal or the sum of the reference signals divided. So the relationship arises

or

Ii "" ^ej "R ₁ +

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For the case of reflection when measuring the moisture content, the data spread decreased from $ 1.5 to about 0.5% Furthermore, the influence of the weight per unit area on the measurement decreased.

When radiographic measurement of fibers in high ash content Paper, the double absorption system reduced the measurement

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Value spread from + 161.5 gm / m (± ¹ 5 gm / ft) to + 43 _f 2 gm / m (+ 4 gm / ft ² ).

In the following, the invention will be described in more detail with reference to drawings explained. Here shows

Fig. 1 is a simplified schematic representation of a preferred Embodiment of the arrangement according to the invention;

Fig.1A shows the arrangement of the filter, the source and the detector j 1B shows a multiple filter arrangement:

Figure 2 is a graphical representation of the absorption and dual reference signals;

3A shows a graphical representation of the moisture measurements of papers with the same percentage moisture, but different paper grades;

3B results obtained with a fluoroscopic arrangement for paper when influenced by the ash content , and

3C shows the noticeably improved course when using a accumulated double absorption, the reference wavelength lying between the absorption wavelengths.

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In Pig. 1 is the arrangement shown by measurement material to be tested is a moving belt 10 made of a sheet-like material such as paper. The band 10 can Drying rolls 13 and 14 adjacent locations are measured.

A light source 15 is designed as a mixed frequency source and emits radiation in the entire infrared spectrum. It is now known that specific frequencies of radiation within the spectrum are absorbed as a result of specific properties will. The specific property of the present preferred embodiment to be measured and evaluated is that percentage of water content in the paper tape, the water weight, the paser weight or in other words the paser and the Humidity. The one on moisture and fiber absorption related wavelengths are known. The wavelengths related to other components or constituents within the Infrared spectrum are also generally known.

Like in Pig. 1 and partly also in Pig. 1A is shown, a plurality of infrared filters 27 is between the light source 15 and the paper tape 10 in the region of the light source 15 arranged. Each of these pilter 27 has a pass band, the radiation of a wavelength related thereto the tape 10 can hit. The one that hits the belt 10 Radiation is backscattered by this and detected by a detector 19. In a fluoroscopic arrangement, the radiation entering the tape is detected. In a practically realized embodiment, the plurality of pilter is 27 arranged on a disk 28 driven by a motor 29. As schematically in Pig. 1B, the rotary filter several pilter 27a ... 27n which correspond to three or more properties or components to be measured. the

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Disc 28 is driven by the motor 29 so that a continuous radiation over the entire spectrum passing through the filter 27 results. To capture and receive everyone Frequencies, a single detector 19 is used. The detector 19 is via a timer 16 with the movement of the rotary filter 27 synchronized. Alternatively or for reasons of simplification, three detectors 2, 23 »25 can be provided, each record a specific frequency of interest.

Facilities with the help of which a multitude of frequencies of the Infrared spectrum can be hidden are known. One of these devices is described in U.S. Patent 3,405,268; In addition to the radiation source, there is a collimating lens, an interrupter and a beam splitter used, which splits the energy beams emitted by the collective lens into three separate beams.

The one in Pig. The embodiment illustrated in FIG. 1 illustrates a "backscatter" system This type of system is specific to nuclear radiation assemblies known, in which the thickness of the material to be examined prevents the passage of radiation. Rtickstrahlmeßanordmingen are still common used when a top layer applied to a base material, such as tin on steel or dust (clay) on paper is to be measured.

As usual with backscatter measuring arrangements, the radiation hits the source 15 on the paper 10 and what is from the paper 10 is not absorbed or passes through the paper 10 is reflected from the surface of the paper. The property and the meaning of the reflected beam is detailed in the pending patent application 874 357 (now continuation-

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in-part application no.) and in patent 3,597,616, but has no direct connection with the present preferred embodiment.

When using infrared measuring arrangements not modified according to the invention for measuring the humidity of paper, erroneous deviations of neighboring samples occurred. For moisture measurements Although there was a much smaller scatter due to the "quality", one observed one general predominant basis weight effect.

In researching the above-mentioned discrepancy, it was found that the paper sheet orientation affected the final display. There were four different ads specifically received, depending on whether the smooth or rough side (feit or wire side), or whether the detectors of the production line are parallel or perpendicular to the machine direction were arranged.

An obvious irregularity was the change in the ambient humidity due to short-term humidity and temperature changes. Since an infrared source gives off heat, it has been suggested that the radiated heat is inside the sample Could dry by about $ 1 in a few minutes. The disturbances from ambient humidity resulted from daily changes the measuring room humidity. To overcome these disturbances, a measuring room with constant humidity was constructed and test measurements carried out for confirmation.

A system for compensating for plasticizer changes had a pass band at 1.94 μ for the absorption wavelength and a passband at 2.25μ for a reference wavelength. When examining the sample data obtained, it was noted that that despite the large distance between the wavelengths

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differential diffraction backscattering occurred. It was also taken into account that 2.25 μ in the area of a weakened Cellulose absorption was.

Further investigations of the shorter wavelengths showed that the daben scattering for 1.84 / 1 »94 μ is a mirror image of that at 1.94 / 2.25μ represented.

The infrared sample measurement system has now been changed to that shown in FIG. 1A and 1B are modified to the preferred embodiment shown. A three-channel arrangement was specifically provided in which the disc 28 of the filter 27 has three filters 27a, 27b and 27c, which let through 1.84, 2.09 and 1.94 μ. The mean wavelength represents the absorption wavelength while the longer and shorter wavelengths take the scattering into account as reference frequencies.

In Fig. 2 the reflection of the absorption spectrum is shown graphically. The signals R ₁ , A, Rp with the three wavelengths are also entered in relation to the spectrum. As can be seen from FIGS. 1, 1A and 1B, the backscattered absorption signal A is detected and compared _{with the reference signals R 1} and R _{2 in a computer circuit which forms a ratio.} Since two reference signals R ₁ and Rp are used in the preferred embodiment, they are summed in a summing amplifier 33. The ratio is then formed by comparing the sum of the two reference signals R ₁ and Rp with the absorption signal from an amplifier 31. A ratio circuit 41 thus specifically forms the ratio function

7 ^ s? ? rt? —τ · This ratio signal can then be applied to a measuring

^ v ₁ + OV ₂ ;

instrument 51 can be visibly displayed or further processed as required. The value of C of the above ratio can be

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be adjusted so that DER Fasergewiehtseffekt over a considerable range through moisture, about 5 to 20 $, and the paper material basis weight, such as from 15 to 80 # per 279 m ² (1300 ft ²⁾ is exactly compensated for.

In the summing amplifier 33, the reference gain is changed by three to double the reference signals and a little lower To compensate for the absorption pulse.

The backscatter data due to basis weight, whitener and plasticizer decreased, as in Pig. 3, in the arrangement of FIG. 1 using two reference signals, to a total of about 0.5 ° of moisture. These scatter values used to be $ 1.5 and more. The preferred embodiment according to FIG. 1 almost completely suppresses the basis weight effect.

In another preferred embodiment for measuring a paper with a high concentration of clay, a reflection wavelength of 1.1 μ is used and 1.2 μ absorption wavelength transilluminated. The basis weight measurement (fibers plus moisture) became strong influenced by changes in the weight, which led to data spreads of + 161.5 gm / m (+15 gm / ft). The described Embodiment used double absorption at 1.0 µ and 1.2 µ. The data spread decreased to +43.2 gm / m (+ 4 gm / ft) in a measuring system with practical Utility.

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Claims (10)

-, 1 j - claims 1.J Arrangement for measuring a material property, marked by an infrared radiation source (15) and one arranged in front of the infrared radiation source (15), the infrared radiation beam splitter (28,29) splitting into at least three separate beams »wherein at least one of the beams a wavelength that can be absorbed according to the material property and the other rays to other properties of the Materials (10) have related wavelengths, by a detector (19) which detects at least part of the radiation not absorbed by the material (10) from each of the beams recorded, by a summation amplifier connected to the detector (19) (33), which sums the signals of the other rays of radiation detected, by a ratio circuit (41), the ratio of the detected signal of the absorption beam of radiation and forms the summation signal of the summation circuit (33), and by a display device (51) for displaying the ratio signal the ratio circuit (41) f wherein the ratio signal is free from deviations due to the material property other properties of the material (10) indicates. 2. Arrangement according to claim 1, characterized in that at least two of the beams according to the material property have absorbable wavelengths. 309844/1133 3. Arrangement according to one of claims 1 or 2, characterized in that that the infrared radiation source (15) and the detector (19) are arranged on the same side of the material (10) are and the detector (19) backscattered by the material (10) Radiation detected. 4. Arrangement according to one of claims 1 or 2, characterized in that that the infrared radiation source (15) and the detector (19) on opposite sides of the material (10) are arranged and the detector (19) detects radiation passing through the material (10). 5. Arrangement according to one of claims 1 to 4 »characterized in that that amplifiers (31) are provided which amplify the signals of the detector (19) corresponding to the beams. 6. Arrangement according to one of the preceding claims, thereby characterized in that the display device (51) is a display device. 7. Arrangement according to one of the preceding claims, characterized in that the beam splitter (28,29) a Has filter disc (28) and a drive (29) for rotating the filter disc (28). 8. Arrangement according to one of the preceding claims, characterized in that the beam splitter (28,29) the Infrared radiation divides into three rays, and that one of the rays is one between the wavelengths of the other two Rays lying wavelength. 9. Arrangement according to one of the preceding claims, there- 309844/1133 characterized in that the wavelengths of the at least three beams are adjacent. 10. The arrangement according to claim 9 »characterized in that the wavelength of one of the beams is approximately 2.28 μ and that the wavelengths of the other two beams are of the order of 1.84 / 1.94 μ and 1.94 / 2.25 μ. 309844/1133 Blank page