JP3183853B2 - In-line particle size distribution analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the particle size of a granular material, and more particularly, to a technique for mounting a powdery substance in a fluidized bed or in a pneumatic transport pipe attached to a fluid treatment device or an air transport pipe. The present invention relates to an in-line particle size distribution measuring device capable of accurately and accurately measuring the particle size distribution of a body in real time.

[0002]

2. Description of the Related Art Conventionally, in the particle size distribution measurement performed when adjusting the particle size of a granular material represented by sugar, corn starch, chemicals, etc., the granular material is measured from a fluidized bed or an air transport pipe each time. Is sampled and measured by a laser beam type particle size sensor installed in an inspection room or the like, and the measured powder or granular material is returned to the fluidized bed processing apparatus again.

However, this method has a serious problem that not only the sampling itself is troublesome, but also that the particle size distribution in the fluidized bed cannot be grasped in real time.

Therefore, a technique has been considered in which a measuring unit of a particle size distribution measuring device is attached to a fluid processing device or a pneumatic transport pipe in an in-line manner to directly measure a powder in a fluid state or a transport state. .

[0005]

However, when this in-line method is adopted, particles flowing or moving in a fluidized bed or a pneumatic transport pipe adhere to a shielding glass provided in a measuring section and become contaminated. Therefore, there is a large problem that the scattering state of the laser light is affected and a large factor of measurement error is caused.

Accordingly, the present invention is to prevent the contamination due to the adhesion of the granular material to the shielding glass provided in the measuring section,
It is an object of the present invention to provide an in-line particle size distribution measurement device capable of performing highly accurate particle size distribution measurement in real time.

[0007]

In order to achieve the above object, the present invention employs the following means. In claim 1,
First, a pair of opposed cylindrical measuring heads through which a laser beam output from a laser beam generator passes is provided, and scattering generated by powder particles entering an open transmission path formed between the measuring heads. A particle size distribution measuring device that collects light, detects a scattering angle, and measures the particle size of the granular material is provided, and the pair of measuring heads are protruded inside the fluidized bed processing device. Each measurement head includes a shielded transparent glass disposed so as to be orthogonal to the laser beam, an outer cylindrical portion extending toward the open transmission path so as to surround the front of the shielded transparent glass, and a radially inner side from the outer cylindrical portion tip. An annular hollow portion formed of an inner cylindrical portion extending so as to approach the shielding transparent glass side by wrapping around, and at least one air inflow hole formed in the outer cylindrical portion, A laminar airflow from the front surface of the shielded transparent glass toward the open transmission path is formed in the inner cylindrical portion. That is, the air sent from the air inflow hole by a predetermined method is blown out through the gap between the inner cylindrical portion tip and the shielding transparent glass while flowing in the hollow portion provided in the annular shape in the measuring head, It blows evenly from the entire circumferential direction to the surface of the shielding transparent glass, or forms a laminar air flow from the shielding transparent glass to the open transmission path. This laminar air flow prevents the granular material that has entered the open transmission path from entering the measuring head, and does not create a swirl of air on the surface of the shielded transparent glass, so that no dust is trapped. . According to the second aspect, a pair of opposed cylindrical measuring heads through which the laser light output from the laser light generating device passes are provided, and the powdery and granular materials that enter the open transmission path formed between the measuring heads are provided. A scattered light generated is collected, a scattering angle is detected, and a particle size distribution measuring device for measuring the particle size of the granular material is provided. The measuring head is configured to transport the powder so that the open transmission path crosses the powder transport path. Attach to pipe. The configuration of each measurement head is the same as that of the first aspect, and a laminar air flow from the front surface of the shielded transparent glass to the open transmission path is formed in the inner cylindrical portion. By adopting this means, the powder particles moving in the powder transport path do not enter the measuring head when passing through the open transmission path, and the powder particles adhere to the surface of the shielding transparent glass. Disappears. According to a third aspect of the present invention, the inner cylindrical portion forming the optical transmission path in the measurement head is formed in a tapered shape in which the diameter becomes narrower from the shielding transparent glass toward the open transmission path side. Item 2 is an inline particle size distribution measuring device means. By this means, the velocity of the laminar air flow increases from the shielded transparent glass toward the open transmission path side, and the granular material entering the open transmission path is more reliably prevented from entering the measurement head, and the particle size is reduced. Increase the distribution measurement accuracy. According to a fourth aspect of the present invention, there is provided the inline particle size distribution measuring device according to any one of the first to third aspects, wherein a plurality of air inlet holes are provided at equal intervals in a circumferential direction. . By this means, the air blown out through the gap between the inner cylindrical portion tip and the shielding transparent glass is blown more uniformly from all circumferential directions to the shielding transparent glass surface, or the air is blown to the shielding transparent glass surface. Vortices are not formed, and no dust pools are formed. In claim 5, the scattered light of the laser light generated by the granular material is focused on the light receiving sensor to detect the scattering angle,
An in-line particle size distribution measuring device according to any one of claims 1, 2, 3, and 4, wherein the light receiving sensor is provided with an automatic focusing mechanism. By this means, it is possible to easily adjust the optical axis of the focal point after the condenser lens, which is caused by the deviation of the mirror or the reflection prism used in the optical transmission path for the laser light, and to easily perform the focusing. According to a sixth aspect of the present invention, the automatic focusing mechanism comprises software programmed to automatically focus during the real-time measurement. I do. In this means, in the fluidized bed processing apparatus, the focus shift due to the shift of the optical axis which may be caused by the temperature change or the vibration during the real time measurement is automatically corrected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an overall schematic view of a first embodiment according to the present invention, FIG. 2 is a cross-sectional view of a measuring head section which is a main part of the first embodiment, and FIG. 3 is a light emitting section and a light receiving section of the same embodiment. FIG. 4 is a diagram showing the structure of the channel of the light receiving sensor of the embodiment, FIG. 5 is a flowchart showing the procedure of the automatic focusing mechanism of the embodiment, and FIG. FIG. 7 is an overall schematic diagram showing a modification of the embodiment, and FIG. 8 is an overall schematic diagram of a second embodiment according to the present invention.

A first embodiment according to the present invention described below is a particle size distribution measuring apparatus based on a laser light scattering method, which is an in-line method, that is, a measuring apparatus which serves as a measuring unit in a fluidized bed processing apparatus or the like. This is a device in which the head 2 is provided, and specifically, a device in which an open transmission path 12 (see FIG. 1 and the like) where a laser beam 10 is scattered by a granular material 20 is provided in a fluidized bed processing device 18. It is.

The basic principle is that a laser beam 10 emitted from a laser light emitting device 8 (He-Ne laser) disposed in the particle size distribution measuring device main body 1 and passed through a collimator 9 is used.
Is scattered by the granular material 20 flowing in the fluidized bed processing apparatus 18, receives the scattered laser light 10, and measures the particle size of the scattered substance 20 in real time from the intensity or the like. Things.

First, referring to FIG. 1, a first embodiment according to the present invention will be described.
The configuration of this embodiment will be described. In the present embodiment, a measuring head 2 (2a, 2b) provided with an open transmission path 12 is provided to protrude into a fluidized bed processing apparatus 18, and a laser beam is directly applied to a powder 20 flowing in the fluidized bed processing apparatus 18. This device is designed so that it can be irradiated with light 10 and its particle size can be measured in real time.

In other words, according to this apparatus, the powder and granules 2 are removed from inside the fluidized bed processing device 18 during measurement from inside the fluidized bed processing device 18.
The inconvenience of sampling 0 every time and bringing it back to a measurement room or the like for measurement is not only eliminated at once, but also the change in particle size can be continuously measured in real time.

More specifically, first, a laser beam 10 emitted from a laser emitting device 8 (He-Ne laser) is emitted.
Is converted into a clear circular parallel beam having a diameter of about 14 mm by the collimator 9, reflected at a right angle by the first reflecting prism 6 a, subsequently reflected at a right angle by the second reflecting prism 6 b, and transmitted to the measuring head 2 a. Heading.

Subsequently, the laser beam 10 is applied to the measuring head 2a.
Is disposed at an end position on the side of the reflection prism 6a so as to be orthogonal to the laser light transmission path (refers to a path through which the laser light 10 passes), passes through the shielding transparent glass 3a, and transmits light inside the measurement head 2a. After passing through the channel, it proceeds to the open transmission channel 12 which is open to the fluidized bed processing device 18.

The open transmission line 12 is connected to the fluidized bed processing device 1
8 is a part of the optical transmission line completely opened, into which the granular material 20 flowing by the flow device enters, and where the scattered light is generated by the granular material 20, that is, the particle size measuring point Becomes

Subsequently, the laser beam 10 including the scattered light that has passed through the open transmission path 12 passes through an optical transmission path formed inside the other measurement head 2b facing the measurement head 2a, and then passes through the shielding transparent glass 3b. Pass through. The laser light 10 that has passed through the shielding transparent glass 3b is condensed by the condensing lens 7 and proceeds toward the light receiving sensor 21.

Here, the scattered light is applied to individual powder
The scattering patterns generated by the scattering are all combined, and this scattering pattern can be calculated depending on the size of the particles. That is, the open transmission path 1
If there are particles of various sizes in 2, laser light 1
0 causes the scattering pattern to be caused by each particle forward.
The scattered light having the combined scattering pattern is condensed by the front condenser lens 7 and measured as a scattered light intensity distribution corresponding to the scatter angle by a light receiving sensor 21 (described later) formed in a multiple ring shape. The particle size distribution is calculated from the scattered light intensity distribution corresponding to the scattering angle.

The delicate analog signal detected by the light receiving sensor 21 (each channel described later) is converted into an electric signal by the high-speed data processing unit 27 (see FIG. 3) and amplified by an amplifier (not shown). Thereafter, the data is converted into a digital value by an AD converter (not shown), sent to the personal computer 26 via a data processing device / transfer device (not shown), and the particle size distribution is calculated.

Here, mainly with reference to FIG. 2, the configuration of the measuring head 2 (2a, 2b) which is a main part of the present embodiment will be described in detail. The measuring head 2 (2a, 2b)
It has a substantially cylindrical shape as a whole, and is arranged so as to face each other across a space forming an open transmission line 12 provided at the center in the left-right direction.

The reflecting prism 6 of each measuring head 2a, 2b
Near the end on the (6a, 6b) (see FIG. 1) side, the shielding transparent glass 3 (3a, 3b) is arranged so as to be orthogonal to the optical transmission path. The shielding transparent glass 3 functions as a partition wall separating the apparatus main body 1 and the inside of the fluidized bed processing apparatus 18 and plays a role of preventing the intrusion of the particles 20.

However, this shielding transparent glass 3 (3a, 3a
b) is the measurement granular material 2 entering the open transmission line 12
If 0 is attached and contaminated, an error occurs in the measurement and the measurement accuracy is lowered. Therefore, it is necessary to always keep a clear state. That is, since the present embodiment is an in-line type particle size distribution measuring device for directly measuring the powder 20 flowing in the flow device interior 18, the shielding transparent glass 3 (3a, 3b)
It is essential to solve the problem of dirt.

Therefore, in the present embodiment, the following contrivance is applied to the measuring head 2 (2a, 2b).
That is, each of the measuring heads 2a, 2b is formed so as to extend toward the open transmission path 12 side from the respective shielding transparent glass 3a, 3b to form the outer cylindrical portion 4a, 4b. Then, the outer cylindrical portion 4a,
4b are bent at right angles inward in the radial direction, and further extended so as to approach the shielding transparent glass 3a, 3b side.
a and 5b are formed.

Thus, an optical transmission path that opens to the open transmission path 12 is formed inside each of the measuring heads 2a and 2b, and the outer cylindrical section 4a, the inner cylindrical section 5a, and the outer cylindrical section are formed around the optical transmission path. Annular hollow portions 13a and 13b surrounded by the inner cylindrical portion 5b and the inner cylindrical portion 5b are formed.

Here, each of the outer cylindrical portions 4a and 4b has an air inlet hole 15 facing each hollow portion 13a and 13b.
(15a, 15b) are formed, and air (compressed air) supplied from a compressor (not shown) is ejected from the air inflow hole 15 and flows into the hollow portions 13a, 13b.

The air that has flowed into the hollow portions 13a and 13b flows in the hollow portions 13a and 13b,
a, 5b, end portions 2 facing the shielding transparent glass 3a, 3b
2 (22a, 22b) and the gap 23 (23a, 23b) formed between the shielding transparent glass 3a, 3b.

By this means, the shielding transparent glasses 3a, 3a
It is possible to form a uniform laminar air flow 14 having a relatively low velocity from the entire circumferential direction of b to the inside in the radial direction. Therefore, a smooth air laminar flow 14 toward the open transmission path 12 is formed along the inner cylindrical portions 5a, 5b without forming a vortex of air on the surfaces of the shielding transparent glasses 3a, 3b. The entry of the powder 20 into the measuring heads 2a and 2b is prevented.

In other words, since no air vortex is formed on the surfaces of the shielding transparent glasses 3a and 3b, no air bubbles are formed due to the intrusion of the powder 20 and the surfaces of the shielding transparent glasses 3a and 3b are always cleared. Can be kept in a state.

If a plurality of air inlet holes 15 are provided in the outer cylinder portion 4 at equal intervals in the circumferential direction, the shielding transparent glasses 3a, 3a
b, the speed from the entire circumferential direction toward the inside in the radial direction is low,
A more uniform laminar air flow 14 can be formed.

Further, since the inner cylindrical portions 5a and 5b are formed in a tapered shape in which the diameter becomes smaller from the shielding transparent glasses 3a and 3b toward the open transmission line 12, the inner laminar flow 1
In No. 4, the flow velocity increases toward the open transmission line 12 side, and becomes maximum at a position facing the open transmission line. As a result, the powder 20 is scattered, and the shielding transparent glass 3a, 3b
Invasion to the side can be prevented more effectively.

Hereinafter, the configurations of the light receiving section and the automatic focusing mechanism of the present embodiment will be described mainly with reference to FIGS. First, the light receiving section will be described. The collimator 9 emits light from a laser light emitting device 8 (He-Ne laser).
Is passed through the condenser lens 7 and forms a focal point 24 at the point. The light receiving sensor 21 is installed in accordance with the focal length F. The light receiving sensor 21 is provided with a sensor including a plurality of channels.

More specifically, the center of the light receiving sensor 21 has a first channel (with a radius of about 90 microns) 21a, and a concentric second channel sensor 21b is formed outside the first channel 21a. The sensor 21c of the semi-concentric third channel (also 21d, 21e,
21f), and a total of 32 channels of sensors are provided alternately in a multiplex ring shape spreading outward. As for the value of the sensor 25, a total of 32 channels of sensor values are sent to the personal computer 26 and analyzed by a sensor value reading command from the personal computer 26.

Next, the automatic focusing mechanism 11 attached to the light receiving sensor 21 is provided with a moving stage 11 for the X axis and the Y axis.
a, and a stepping motor 11b capable of moving the stage back and forth by 20 microns per step.

The laser beam 10 focused at the position of the focal length F
Is the first channel 2 at the center of the light receiving sensor 25 described above.
When concentrated on 5a, the value becomes the maximum, and the state where the value of the second channel outside it becomes the minimum is the state where the focus 24 is in focus. The focal point 24 is moved to the first channel.

The procedure of the above-described automatic focusing will be described with reference to the flowchart of the automatic focusing shown in FIG.
First, in step 1 (hereinafter referred to as "S1"), the moving stage 11a is moved up, down, left and right by the stepping motor 11b to read the sensor values at each point. In S2, the sensor is moved to the position closest to the focal point 24. Subsequently, in S3, the moving stage 11a is moved up, down, left, and right again to read the sensor values at each point. Then, in S4, it is determined whether or not the current position is the point closest to the focal point by comparing it with a previously input maximum value. In the case of YES, the automatic focusing is ended in S5. Go back and focus.

In this embodiment, the automatic focusing mechanism 11 described above is provided with the automatic focusing mechanism 11 in the light-receiving sensor 21 which collects the scattered light on the sensor 25 and detects the scattering angle. Can be done.

However, since the condenser lens 7 and the reflecting prism 6 are used in the laser light transmission path, if a slight displacement of these members occurs due to a temperature change or vibration during the measurement, the optical axis is shifted. As a result, a shift of the focal point 24 of the light receiving section is caused. Therefore, if focusing can be performed automatically even during real-time measurement, stable real-time measurement can be performed in the in-line type particle size distribution measurement.

On the other hand, whether or not the focal point 24 is deviated during the real-time measurement can be determined by measuring to which part of the light receiving sensor 21 the laser light 10 is focused. Are focused when the laser beam 10 is focused on the focal point 24 at the center of the laser beam.)

Therefore, when the optical axis shifts during the real-time measurement and the focus 24 becomes out of focus, the automatic focusing mechanism 11 is controlled by software which is programmed to automatically operate the automatic focusing mechanism 11. Then, automatic focusing during the real-time measurement is performed.

The procedure of automatic focusing during measurement will be described below with reference to FIG. First, in S10, the measurement interval T
Seconds and the number of measurements N are set, and in S11, automatic focusing is performed to set the device in a measurable state. Then, in S12, continuous measurement is started. Then, it is determined in S13 whether or not the focus is in focus.
The particle size distribution measurement of 0 is started, and the particle size distribution is calculated in S15.

When the calculation in S15 is completed, it is determined in S16 whether the number of measurements has reached a predetermined N times, and if it has reached N times, the automatic focusing in S17 is ended.
On the other hand, if the determination in S13 is NO, that is, if the focus is out of focus, the automatic focusing similar to the above S1 to S5 is performed again in S18, and then the process proceeds to S14 and S15.

If the number of measurements has not reached the predetermined N times in S16, it is determined in S19 whether a predetermined measurement interval T seconds has elapsed.
13 and proceed as above. On the other hand, if the measurement interval has not reached T seconds, it is determined whether T seconds have elapsed again, and after the elapse of T seconds, the process returns to S13 and proceeds as described above.

In the automatic focusing mechanism of this embodiment,
Although the above procedure is performed, the present invention is not necessarily limited to this procedure, and a focusing algorithm can be appropriately selected.

Next, a modification of the first embodiment shown in FIG. 7 will be described. The difference from the above embodiment is that the flow device 1
The arrangement of the measuring heads 2 (2a, 2b) protruding into the interior 8 is described. That is, in the embodiment shown in FIG. 1, while the optical transmission path between the measuring heads 2a and 2b is configured to be orthogonal to the side wall 18a of the fluidized bed apparatus 18,
The present modification is different in that the optical transmission path between the measuring heads 2 (2a, 2b) is configured to be in a direction along the side wall 18a of the fluidized bed processing device 18.

A laser beam 10 emitted from a laser emitting device 8 (He-Ne laser) and passing through a collimator 9
However, in the embodiment shown in FIG. 1, the light is reflected at a right angle by the first reflecting prism 6a, and subsequently, reflected by the second reflecting prism 6a.
b, the light is reflected at a right angle, and the measuring heads 2a, 2b pass through the optical transmission path and travel toward the condenser lens 7. On the other hand, in this modification, the light is reflected at a right angle by the first reflecting prism 6a. Then, after passing through the optical transmission paths in the measuring heads 2a and 2b, the light is reflected at a right angle by the second reflecting prism 6b.
It is also different in that the configuration is directed toward the condenser lens 7.

The other structure is the same as that of the first embodiment. In consideration of the modified example and the above-described embodiment, it is possible to appropriately select a method of arranging the measuring head 2 depending on the internal structure of the fluidized bed processing apparatus 18 and the like.

Next, a second embodiment according to the present invention shown in FIG. 8 will be described. Reference numeral 17 shown in FIG. 4 indicates a powder transport path made of a pipe or the like. In the present embodiment, the measuring heads 2a and 2b are arranged to face each other in the middle of the powder transport path 17 so as to sandwich the transport path 17,
Are provided at right angles to the laser beam 10 transmission line.

That is, the space portion 19 of the powder transport path 17 sandwiched between the measuring heads 2a and 2b plays the role of the open transmission path 12, and the granular material 20 being transported is irradiated with the laser beam 10 and scattered. Light is generated.

The structure of the measuring heads 2a and 2b of the present embodiment is the same as that of the first embodiment, and the description thereof will be omitted by retaining the same reference numerals.
The same applies to the configuration of the automatic focusing mechanism 11 and the focusing procedure. Thus, the particle size distribution of the powder 20 during pneumatic transportation can be measured in real time, so that it is also suitable for measuring the particle size distribution of the powder 20 such as toner.

[0049]

The effects of the invention disclosed by the present application will be listed and described as follows. (1) A pair of measuring heads are protruded inside the fluidized bed processing apparatus, and air sent by a predetermined method from an air inlet hole provided in the measuring head flows in a hollow portion provided in the measuring head in an annular shape. While blowing out through the gap between the inner cylindrical portion tip and the shielding transparent glass, the air layer blows evenly from the entire circumferential direction to the shielding transparent glass surface, and goes from the shielding transparent glass to the open transmission path. Since the flow is formed, it is possible to prevent the granular material entering the open transmission path from entering the measuring head, and to prevent the particulate material from being trapped on the surface of the shielding transparent glass. Therefore, the surface of the shielding transparent glass can always be kept in a clear state, and highly accurate real-time particle size distribution measurement without measurement error can be performed.

(2) The measuring head is attached to the powder transport pipe so that the open transmission path crosses the powder transport path.
A similar air laminar flow is generated in the measuring head to prevent the intrusion of the granular material into the measuring head, and to prevent the formation of dust accumulation on the surface of the shielding transparent glass. The particle size distribution of the powder moving in the transportation path can be accurately measured in real time.

(3) The inner cylindrical portion formed in the measuring head is formed in a tapered shape in which the diameter decreases from the shielding transparent glass toward the open transmission path side, so that the velocity of the laminar air flow is reduced. , The size of the particle increases toward the open transmission path side, so that the particles entering the open transmission path can be more reliably prevented from entering the measurement head, and the measurement accuracy of the particle size distribution can be further improved.

(4) By providing a plurality of air inlet holes at equal intervals in the circumferential direction in the outer cylinder portion of the measuring head, more uniform air can be blown to the shielding transparent glass from all circumferential directions of the shielding transparent glass. Therefore, the measurement accuracy can be further improved.

(5) Scattered light of laser light generated by the granular material is focused on a light receiving sensor to detect a scattering angle, and a program is set in the light receiving sensor to automatically operate an automatic focusing mechanism. The automatic focusing mechanism controlled by the software automatically detects the deviation of the optical axis caused by the deviation of the mirror and reflection prism used in the laser light transmission path due to temperature change and vibration during real-time measurement. Since the focusing can be performed by appropriately adjusting the size, highly accurate real-time measurement of the in-line type particle size distribution device can be performed continuously and stably for a long time.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of a first embodiment according to the present invention.

FIG. 2 is a cross-sectional view of a measuring head part, which is a main part of the embodiment.

FIG. 3 is a block diagram showing a light emitting unit and a light receiving unit of the embodiment.

FIG. 4 is a diagram showing a structure of a channel of the light receiving sensor of the embodiment.

FIG. 5 is a flowchart showing a procedure of the automatic focusing mechanism of the embodiment.

FIG. 6 is a flowchart showing a procedure during measurement by the mechanism.

FIG. 7 Overall schematic diagram showing a modification of the embodiment

FIG. 8 Overall schematic diagram of a second embodiment according to the present invention

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 particle size distribution measuring device main body 2 (2a, 2b) measuring head 3 (3a, 3b) shielding transparent glass 4 (4a, 4b) outer cylindrical portion 5 (5a, 5b) inner cylindrical portion 8 laser light generator 10 laser light 11 Automatic focusing mechanism 12 Open transmission path 13 (13a, 13b) hollow part 14 Air laminar flow 15 (15a, 15b) air inflow hole 16 Tip of outer cylinder part 17 Particle transport path 18 Fluidized bed processing device 20 Powder and granular material 21 Light receiving sensor 22 (22a, 22b) gap 23 (23a, 23b) inner cylindrical portion tip

Claims (6)

(57) [Claims] 1. A pair of opposed cylindrical measuring heads through which a laser beam output from a laser beam generator passes is provided, and a powdery material entered into an open transmission path formed between the measuring heads. A particle size distribution measuring device that collects the scattered light generated, detects the scattering angle, and measures the particle size of the granular material, wherein the pair of measuring heads are protruded inside the fluidized bed processing device. Each measurement head is provided with a shielded transparent glass disposed so as to be orthogonal to the laser beam, an outer cylindrical portion extending toward the open transmission path so as to surround the front of the shielded transparent glass, and a radially inner side from a tip of the outer cylindrical portion. An annular hollow portion formed of an inner cylindrical portion extending so as to approach the shielding transparent glass side by wrapping around, and at least one air inflow hole formed in the outer cylindrical portion. The inside of the inner cylinder portion is shielded. From the front of the transparent glass, inline particle size distribution measuring apparatus, wherein an air layer flow toward the open transmission paths are formed. 2. A pair of opposed cylindrical measuring heads through which a laser beam output from a laser beam generator passes is provided, and a powdery or granular material entered into an open transmission path formed between the measuring heads. A particle size distribution measuring device that collects the scattered light to be generated, detects the scattering angle, and measures the particle size of the granular material, wherein the open transmission path is provided so as to cross the powder transport path. Each measurement head is provided with a shielded transparent glass disposed so as to be orthogonal to the laser beam, an outer cylinder portion extending toward the open transmission path so as to surround the front of the shielded transparent glass, and a radially inner side from the tip of the outer cylinder portion. An annular hollow portion formed by an inner cylindrical portion extending around and approaching the shield transparent glass side; and at least one air inflow hole formed in the outer cylindrical portion; Shielding transparent inside the inner cylinder From the front of the lath, inline particle size distribution measuring apparatus, wherein an air layer flow toward the open transmission paths are formed. 3. The in-line particle size distribution measuring device according to claim 1, wherein the inner cylindrical portion is formed in a tapered shape in which the diameter decreases from the shielding transparent glass toward the open transmission path side. . 4. The air inlet according to claim 1, wherein a plurality of air inlet holes are provided at equal intervals in a circumferential direction.
The inline particle size distribution measuring device according to claim 3. 5. The light-receiving sensor according to claim 1, wherein said scattered light is collected on a light-receiving sensor to detect a scattering angle, and said light-receiving sensor is provided with an automatic focusing mechanism. 3. An in-line particle size distribution measuring device according to claim 4. 6. An in-line particle size distribution measuring apparatus according to claim 5, wherein said automatic focusing mechanism comprises software programmed to automatically focus during real-time measurement.