DE2603221A1 - METHOD AND DEVICE FOR DETERMINING THE GRANULOMETRIC DISTRIBUTION IN MIXTURES - Google Patents

Description

Fo 9699 D 2 Jan. 9, 1976

Dipl.-Ing. Jürgen WEINMILLER

PATENT ASSESSOR O C Π O O O 1

«OSPIGmbH 2603221

8OGO Munich 80
Zeppeiinstr. 63

COMPAGNIE INDUSTRIELLE DES LASER Route de Nozay, 91460 MäRCOUSSIS France

METHOD AND DEVICE FOR DETERMINING THE GRANULOMETRIC DISTRIBUTION IN MIXTURES

The invention relates to a method and a device for determining the particle size distribution in Mixtures, i.e., to determine the values of a curve that depending on the diameter of the particles present in the mixture, the proportions of the particles of a certain diameter reproduces.

It is a device for determining the granulometric Distribution in a suspension-like particle mixture present in a liquid known, which is a light source for monochromatic light, a transparent container containing the mixture placed in the path of the light beam is, a convergence optical system for producing a

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Diffraction spot of the illuminated mixture at the focal point, a diaphragm located in this focal point and displaceable in the focal plane, the opening width of which is variable and which has a part of the spot delimiting section of a circular crown, a light receiver for Receiving the light from this patch and emitting electrical signals that determine the received light intensity reproduce when the diaphragm is shifted in the focal plane to examine the diffraction spot, as well as a Computer includes, based on these signals, the proportion of the particles contained in the mixture different Can determine diameter.

However, as the concentration of the particle mixture decreases, so does the sensitivity of the above-mentioned apparatus bad that the measured values are no longer meaningful.

The aim of the invention is to eliminate this disadvantage and to specify a method with which with great accuracy the particle size distribution of a particle mixture is determined even if the concentration of the particles in the mixture is very low.

Another object of the invention is a device for using this method.

The invention relates to a method for determining the granulometric distribution of a particle mixture which is present as a suspension in a liquid, the method comprising at least partial steps
- put the mixture in a transparent container,

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which is arranged in the path of a monochromatic light beam will,

- one in the focal plane of a converging optical system To create a diffraction spot of the illuminated mixture,

- that of a receiver in response to the light of a section to process the said spot emitted electrical signals, this section through the opening of a arranged on the spot aperture is limited and the circumference of this opening has the shape of a section of a on the focal point of the converging optical system has centered circular ring sector-shaped crown,

characterized in that the mixture in the container is caused to flow through the light beam, the Cross-section of the flow of this mixture is sufficiently small to allow the particles of the mixture in the container to flow are displaced, successively wandering through the light beam, the electrical signals passing through these particles and the amplitude of these signals is an increasing function of the diameter of the particles, and that the processing of the electrical signals comprises several stages, each consisting in the passage of a predetermined one Amount of mixture to count the number of signals whose amplitude exceeds a predetermined threshold value.

The invention also relates to a device for determining the particle size distribution of a particle mixture, which is in suspension in a liquid, the device comprising

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- a source for a monochromatic light beam,

- a transparent container that holds the mixture and is placed in the path of the light beam,

a converging optical system for the formation of a diffraction spot in its focal plane by the light beam illuminated mix,

- A diaphragm, the opening of which is a cutout in the focal plane of the diffraction spot limited,

- A light receiver which is arranged so that it is through the Aperture receives the light of the patch section, the opening of this aperture through a section of one on the Focal point of the converging optical system centered circular crown is limited,

- Means with which the dimensions of the opening of the diaphragm changed can be

- means for processing the electrical signals sent by the receiver in response to the light, characterized in that means are also provided by which the mixture in the container passes through the light beam is set in motion, the electrical signals passing through the individual passages of the particles of the mixture in the Container are generated by the light beam, and that the means for processing the electrical emitted by the receiver Signals comprise a counter, the input of which is connected to the output of the receiver via a threshold device, in order to determine during the passage of a predetermined amount of the mixture the number of signals whose amplitude is greater than is a predetermined threshold, and that means for setting

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this predetermined threshold value are provided.

The invention is explained in more detail below with reference to the accompanying three figures.

Fig. 1 shows schematically an embodiment of the invention Contraption.

FIG. 2 shows a component of the device shown in FIG. 1.

Fig. 3 shows a family of curves, with the help of which the invention Procedure can be evaluated.

1 shows a device which has a source for a monochromatic light beam 1. These The light source comprises a laser generator 2 which emits a laser beam 3, on whose path an afocal optical system is arranged which can reduce the cross section of the laser beam 3. This afocal optical system consists of two lenses 4 and 5, which are centered on the axis 6 of the light beam 3, a focal point 7 of the lens 4 coinciding with a focal point of the lens 5. The opening of a spatial filter, which is formed from a diaphragm 8, is at the common focal point 7 of two lenses arranged.

On the path of the light beam 1, which leaves the afocal system, a transparent container 9 for receiving a to examined particle mixture housed. A centered on the axis 6 converging optical system 10 can in his Focal plane 11 a diffraction spot of the existing in the container 9 and form mixture enlightened by ray 1.

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In the focal plane 11 of this system, a diaphragm is arranged, the opening 13 of which in the plane 11 is a cutout the diffraction spot limited. This screen can be arranged, for example, on one side of a container 14, the enclosing a receiver 15 which is a photoelectron multiplier can act and its photosensitive surface 16 through the aperture 12 that of the through this aperture limited diffraction spot section can receive emitted light. Between the photosensitive surface 16 and the Diaphragm 12 is advantageously arranged an interference filter 17 which is transparent to the light of the diffraction spot, however, it is impermeable to interference radiation.

A counter 18 is connected to the output of the receiver 15 via a threshold device 19, the means for Setting this threshold includes.

The various optical organs described above are preferably installed on an optical bench 20, which in turn rests on vibration dampers 22. The container 14 can be known with the aid of those shown schematically at 21 Means are moved on the optical bench 20.

Finally, the device also comprises means with which the mixture to be examined in the container 9 is in motion can be moved. These means are a container 23 for the mixture 24 with lines 25 and 26, which connects the container 23 to the container 9 and to a pump 27 built into the circuit. Advantageously, an agitator 28 is installed in the container 23, which is operated with the aid of a motor 29.

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In Fig. 2, the front of the screen 12 is shown to show the shape of its opening 13. This opening is formed by an angle u from a circular ring sector-shaped delimited by two concentric circles Rl and R2 centered on a point Edged crown. The cross-section of the opening 13 can be determined by any known means (not shown here) are changed, in particular the values of the radii Rl and R2. The position of the diaphragm 12 to the optical bench 20 can be determined with the aid of Means 21 are adjusted, which act on the container 14 so that the point 30 on the axis 6 at the focal point of the optical Systems 10 can be brought.

With the device shown in Fig. 1, the granulometric distribution of a suspension-like in a Liquid present particle mixture of low concentration can be measured.

This process can include one or more operations.

With each operation, the mixture is poured into the container 9 and set in flow in this container · The Cross-section of the flow of the mixture in the container 9 must take into account the concentration of the particles in the mixture be sufficiently small that the particles of the mixture i.w. pass light beam 1 one after the other, The agitator 28 accommodated in the container 23 ensures homogeneity of the mixture and local particle accumulations prevented.

Each passage of a particle through the light beam 1 causes a change in the light-sensitive surface

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of the receiver 15 received light intensity of the limited by the opening 13 of the diaphragm 12 diffraction spot section coming light. Electrical signals are thus obtained at the output of the receiver, the amplitude of which has an increasing function is the diameter of the particles. Therefore, if the threshold value of the device 19 is set to a certain value, so the number of particles in the mixture whose diameter is greater than a predetermined value is counted with the aid of the counter 18 ai is the diameter of the particles. This counting takes place during the passage of a predetermined amount of the mixture, i.e. during a predetermined time when the flow volume caused by the pump 27 is constant, which is generally the case is. The proportion of particles in the mixture, their diameter, can be derived from the number Ni counted is greater than ai.

Then the same measurement is carried out for another threshold value that is slightly above the previous one, and thus determines the number Nj of particles whose diameter is greater than aj. One obtains in this way by subtraction the number η = Ni - Nj of particles of the mixture, their diameter lies between ai and aj. It is easy to see that. when the threshold value of the device 19 is adjusted during different stages, it changes to increasing values, which are increasing Diameter values from ai to the maximum diameter of the particles correspond to the mixture, the granulometric is possible Determine the distribution of the mixture for diameter values greater than ai.

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During the various above-mentioned measuring processes, the opening 13 of the diaphragm 12 remains unchanged. The opening widths must be adapted to the diameter of the particles to be counted will.

The radii of the circles R1 and R2 delimiting the circular sector-shaped crown of the diaphragm are as follows certainly :

In a focal plane of an optical system similar to the optical system 10, a diffraction image of a dispersion becomes produced with dispersed particles of diameter A, this dispersion being illuminated by a light beam, which is equal to light beam 1. The value of the diameter A represents an upper limit of the diameter of the particles of the mixture to be examined.

Then in a rectangular coordinate system OPR, where 0 is the origin and P is the percentage of Light energy of the image, which is diffracted in a diffraction circle with the radius R, is drawn a curve P = f (R). The corresponding measurements can be carried out, for example, by placing a in the focal plane of the optical system Aperture is arranged with a circular variable opening. In Fig. 3 four curves P = f (R) are shown, the Corresponding to particle diameters of 4, 8, 16 and 32 microns, respectively.

For example, if one wants to study the particle size distribution of particles in the mixture whose diameter is smaller when the value A = 8 microns, a growing and practically linear part 31, 32 of the curve is projected onto the axis OR for 8 microns; this part of the curve, which is between 20 and 70%

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lying percentage P is projected onto the axis OR in the form of a section 33, 34. The radii Rl and R2 of the circular crown shown in Fig. 2 are chosen equal to the abscissa of points 33 and 34 on the axis OR, where a constant value is taken for the angle u, preferably for all operations of this method.

During an operation, the opening width is the Aperture 12 is the same, and experience shows that the opening widths determined in this way are particularly good for reception by the receiver 15 corresponds to the passage through the light beam in the container 9 of particles whose diameter is smaller than A. Signals is matched, i.e. smaller than 8 microns in the case examined above.

If one wants to determine the particle size distribution of a particle mixture of low concentration, its diameter are staggered between 2 and 32 microns, for example, proceed as follows:

The first step is to draw the curve for 32 microns according to FIG. 3, which is the maximum value for the diameter of the Particle corresponds to the mixture. The opening width of the diaphragm 12 is increased by projection onto the axis OR of FIG. 3 and the practically linear part of this curve is determined. With the aid of the device shown in FIG. 1 with the diaphragm thus determined the particles of the mixture are counted, the threshold value of the device 19 being set to a value that corresponds to the amplitude of the noise signal arriving in the receiver, this noise signal in turn, for example, corresponding to a particle diameter of 16 microns. During that first one

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Operation is the threshold value, successively to between 16 and 32 microns, e.g. 18, 20, 22, 24, 26, 28 and 30 microns, staggered values are set. These take place one after the other Settings correspond to the different stages of this first operation, during which the number of predetermined amount of the mixture contained particles is counted. This first step thus enables the determination the granulometric distribution of the mixture for diameter values from 16 to 32 microns.

This is followed by a second stage of the procedure

applied, during which the aperture width by using a

the curve of the network of Fig. 3 is chosen to be practically the minimum Diameter corresponds to the range of the diameters examined during the previous stage, i.e. using the Curve for 16 microns. With the aid of the device shown in FIG. 1 with the aperture set as indicated above, one goes in the same way as for the first step. The noise signal of the receiver adjusts itself to a lower level, for example to a level corresponding to a particle diameter of 8 microns. This second process thus enables the determination the granulometric distribution of the mixture for diameters from 8 to 16 microns.

Finally, a third and fourth operation are carried out in which the granulometric distribution of the mixture can be determined for diameters from 4 to 8 or 2 to 4 microns. . ■

The correspondence between the noise signal upon reception and the diameter of the particles whose passage through the light

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ray causes the formation of a signal for a given aperture, the amplitude of which is equal to that of the noise signal, i.e. the calibration curve of the receiver, can be determined by an experiment which is uniform with dispersions of particles and defined diameter is carried out with the aid of one of the apparatus corresponding to FIG. 1, in which an oscilloscope 35 is arranged at the output of the receiver 15 in order to measure the amplitude of the electrical received signals.

The invention can be used in the determination of the particle size distribution of particle mixtures, which are suspended in a liquid in a very low concentration.

Patent smells

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Claims (1)

PATENT CLAIMS f 1 j- method for determining the particle size distribution development of a particle mixture, which as a suspension in a liquid is present, the method comprising at least one sub-step - put the mixture in a transparent container, which is placed in the path of a monochromatic light beam, - to create a diffraction spot of the illuminated mixture in the focal plane of a converging optical system, - that of a receiver in response to the light of a section to process the said spot emitted electrical signals, this section through the opening of a Arranged on the stain aperture is limited and the circumference of this opening has the shape of a section of a on the Has the focal point of the converging optical system centered circular ring sector-shaped crown, characterized in that the mixture in the container (9) through the light beam (1) in flow is offset, the cross section of the flow of this mixture is sufficiently small that the particles of the mixture, which in the container (9) are set in flow, successively migrate through the light beam (1), the electrical signals through the passing of these particles are generated and the amplitude of these signals is an increasing function of the diameter of the particles is, and that the processing of the electrical signals comprises several * stages, each consisting of during the 609832/0857 Passing a predetermined amount of the mixture to count the number of signals whose amplitude is a predetermined Exceeds threshold. 2 - Device according to claim 1, characterized in that the dimensions of the opening (13) of the diaphragm (12) remain constant and the radii (Rl and R2) of the circles delimiting the crown depending on a value A of the diameter of the Particles are determined, this determination consisting in that a diffraction image of a dispersion of particles of uniform and defined diameter A is produced in the focal plane of an optical system similar to the converging optical system (10), the mixture being produced by a monochromatic light beam (1) the same light beam is illuminated to draw a curve (P = f (R)) in a coordinate system OPR, where O is the origin of the axes and P indicates the percentage of the light energy of the image diffracted in a diffraction circle with the radius R, where a growing and practically linear part (31, 32) of this curve in the form of a section (33, 34) on the Ac hse OR is projected, the radii (Rl and R2) of the circles delimiting the crown during this operation being equal to the abscissa on the axis OR of the end points (33, 34) of the curve projection section, and that within this operation from one stage to the other of predetermined threshold value successively assumes different values between the amplitude of the noise signal of the receiver (15) and the amplitude of the electrical signal caused by the passage of a particle with the diameter A, the 609832/0 857 Amplitude of the noise signal equal to the amplitude of the passage of a particle with a diameter a ^ A evoked electrical signal. 3 - The method according to claim 2, characterized in that that in a first operation the value A of the diameter of the particles with which the radii (Rl, R2) of circles delimiting the crown can be determined during this first operation, equal to the value Al of the diameter of the largest Is particles of the mixture, the diameter a then having a value al. 4 - · Method according to claim 3, characterized in that that in addition at least a second whereby
Work step is provided, r3er value A2 of the diameter of the particles, with which the radii (Rl, R2) of the circles delimiting the crown during this second work step can be determined, is practically equal to the diameter a1. 5 - Device for determining the granulometric distribution of a particle mixture, which is like a suspension in a Liquid is present, the device comprising - a source for a monochromatic light beam, - a transparent container that holds the mixture and is placed in the path of the light beam, a converging optical system for the formation of a diffraction spot in its focal plane by the light beam illuminated mix, - A diaphragm, the opening of which is a cutout in the focal plane of the diffraction spot limited, 609832/0 857 - A light receiver which is arranged so that it is through the Aperture receives the light of the patch section, the opening of this aperture through a section of one on the Focal point of the converging optical system centered circular crown is limited, - Means with which the dimensions of the opening of the diaphragm changed can be - means for processing the electrical signals sent by the receiver in response to the light, characterized in that means (23, 25, 26, 27) are also provided with which the mixture (24) is set in motion in the container (9) by the light beam (1), the electrical signals through the individual passages of the particles of the mixture in the container (23) are generated by the light beam (1), and that the means (18) for processing the messages sent by the receiver (15) electrical signals comprise a counter (18), the input of which is connected to the output of the receiver (15) via a threshold device (19) is connected to the number of signals during the passage of a predetermined amount of the mixture determine, whose amplitude is greater than a predetermined threshold value, and that means for setting this predetermined Threshold are provided. 6 - Device according to claim 5, characterized in that that the source for the monochromatic light (1) a laser generator (3) and an afocal optical system (4, 5), which is arranged at the output of the laser generator (2) in order to reduce the cross section of this laser beam. 609832 / 08Ö7 7 - Device according to claim 6, characterized in that that the afocal optical system (4, 5), the two lenses centered on the axis (6) of the laser beam (3) wherein a focal point (7) of a lens (4) coincides with the focal point of the other lens (5), moreover comprises a spatial filter (8) which consists of a diaphragm whose opening is at the common focal point (7) of the two lenses (4, 5) is arranged. χ χ 609832/0807