JPH01250735A - Apparatus for measuring particle size - Google Patents

Abstract

PURPOSE:To obtain the title apparatus capable of outputting the accurate particle size value of particles to be measured even when said particles do not correctly pass through a measuring visual field, by calculating the particles size of the particles to be measured from the rising time of a scattering light pulse signal. CONSTITUTION:An operation apparatus 13 calculates the peak value Imax of the scattering light pulse signal S read from a waveform memory apparatus 12 from the data thereof and calculates, for example, the preset points X1, X2 where the 90%- and 10%-threshold values of the value Imax cross each other and the rising time Dw' of the signal S wherein both points are connected by a straight line is calculated by extrapolation. Next, an actual rising time Dw is obtained according to a predetermined formula to set a 50% threshold value to the value Imax and points X3, X4 where the value of the signal crosses said threshold value is calculated to calculate the time tv between them. The passing speed (v) of particles M to be measured is calculated based upon the length Iz of a preliminarily known measuring visual field E and the time tv. Next, the speed (v) and the time Dw are used to calculate the particle size of the particles according to a separate predetermined formula to display the same on a display device 14. Thereby a particle size can be measured with respect to all of the cases wherein the particles M pass in such a state that 1/2 or more of the sizes thereof enters the visual field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a particle size measuring device for measuring the particle size of minute particles.

(Conventional technology) Conventionally, as a method to measure the particle size of microparticles.

A method using scattering of light by particles to be measured is known. One of them is a method called the photo counting method. The main part of a particle size measuring apparatus employing this photocount method is constructed as shown in FIG. That is, in this device, the measurement point is set to P, and the irradiation optical system A is provided on one side with this point P as the boundary, and ft! ! A light receiving optical system B is provided on one side. The irradiation optical system A includes a light source 1.

The light emitted from this light source 1 enters an optical fiber 3 via a lens 2, and this optical fiber 3 transmits an RF signal near the measurement point.
After being guided to l, the light is input to the rectangular waveguide 4. Then, the light exiting the rectangular waveguide 4 passes through a lens 5 and a prism 6.
is guided to point P via

The lens 5 and the prism 6 are arranged in such a relationship that an image of the exit of the rectangular waveguide 4 is formed on a point P.

On the other hand, in the first light-receiving optical system B, the image of point P is incident on the optical fiber 9 via the lens 7 and the slit 8. The lens 7 is arranged in such a manner that the image of the slit 8 is focused on a point P. Therefore, around point P, there is a
), the measurement view of the cube defined by the irradiating optical needle A and the receiving optical needle B! ! E is formed. In this case, due to the presence of the rectangular waveguide 'f#14, the light intensity distribution within the measurement field of view E is kept constant as shown in FIG. 5(b).

This outfit! Now, as shown in FIG. 5(a), when a particle to be measured M passes within the measurement field of view E, the scattered light by this particle to be measured M passes through a lens 7 and a slit 8 to an optical fiber 9.
guided by. The light guided to the optical fiber 9 is then guided to a photodetector 10 made of a photomultiplier tube or the like, and converted into an electrical signal by the photodetector 10. That is, it is converted into a scattered light pulse signal S having a magnitude corresponding to the intensity of the scattered light. The scattered light pulse signal S is then introduced into a signal processing device (not shown). This signal processing device utilizes the relationship shown in FIG. 6 between the magnitude of the scattered light pulse signal S and the particle size, that is, the height of the scattered light pulse signal S is approximately proportional to the square of the particle size. The particle size is calculated using

However, the particle size measuring device configured as described above has the following problems. That is, the particles to be measured M do not always pass through the center of the measurement field of view E. For example, a particle to be measured M1 of a certain particle size may pass through the center of the measurement field of view E as shown by the solid line in FIG. Even if a scattered light pulse signal Sl of height IIaX is obtained, if only half of the measured particle M1 of the same particle size passes through the measurement field of view E as shown by the broken line in the figure, the resulting scattering As shown by the broken line in the height of the optical pulse signal S, I na
It becomes 172 of x. Therefore, there was a problem in that the range in which one particle size could be accurately measured was narrow and reliability was lacking.

(Problems to be Solved by the Invention) As mentioned above, in conventional particle size measuring devices, if the particle to be measured does not enter the measurement field of view correctly, it outputs an erroneous measurement result, making it unreliable. The problem was that it lacked sex.

Therefore, the present invention provides a particle size measuring device that can output the correct particle size value of the measured particle even when the measured particle does not pass through the measurement field of view correctly, that is, even when the entire measured particle does not fall within the measurement field of view. is intended to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the apparatus of the present invention focuses on the rise time of the scattered light pulse signal.

That is, in the apparatus of the present invention, the particle diameter of the particle to be measured is calculated from the rise time of the scattered light pulse signal.

(Function) When a cubic measurement field of view is defined by the irradiation optical system and the light receiving optical system, the use of a rectangular waveguide can make the light intensity distribution in the measurement field of view uniform in the direction of passage of the particle to be measured. It can be easily achieved. There is a relationship shown in FIG. 1 between the waveform of a scattered light pulse signal obtained when a particle to be measured passes through such a measurement field of view and the measurement field of view. That is, in Figure 1, E indicates the measurement field of view, 1M indicates the particle to be measured, and S indicates the waveform of the obtained scattered light pulse signal.

Now, suppose that the particle to be measured M begins to enter the measurement field of view E of length Iz at time t1 and completely enters at one time t3, then the rise time Dw of the scattered light pulse signal S is t.
It is determined by l and t3. On the other hand, the particle to be measured M is in the measurement field of view E.
The time tv required to pass through is.

peak of scattered light pulse signal S @so for Inax
The time difference between two points showing the value of '<, i.e. t2 and 14
It can be found from. Also, the length I of the measurement field of view E
z can be easily determined from the optical system. therefore,
From tv and Iz, the velocity (2) at which the particle M to be measured passes within the measurement field of view E can be determined.1In the end, the diameter of the particle M to be measured is:

D=Owxv (1) This can be calculated as 0. The apparatus of the present invention uses such a calculation method to measure the particle size.

The rise time of the scattered light pulse signal S does not change even if the particle to be measured M passes through the edge of the measurement field of view E when the particle size of the particle to be measured M is the same. Therefore, unlike conventional devices that determine the particle size from the height of the scattered light pulse signal S, J! Even when the particle M to be measured passes through the edge of the constant field E, the particle size can be accurately measured, and reliability can be improved.

(Example) Examples will be described below with reference to nine drawings.

Figure 2 shows a particle size measuring device according to one embodiment! FIG. 4 is a schematic diagram of the configuration of FIG. 4, and the same parts as in FIG. Therefore, a detailed explanation of the overlapping portion will be omitted.

The difference between the particle size measuring apparatus according to this embodiment and the conventional one lies in the processing system C that processes the scattered light pulse signal S output from the five-photodetector 10.

That is, the scattered light pulse signal S output from the photodetector 10 is subjected to current-to-voltage conversion by the amplifier 11 and then introduced into the waveform storage device 12. The waveform storage device 12 performs A/D conversion on the input scattered light pulse signal and then stores it in a digital memory.

The scattered light pulse signal S stored in the waveform storage device 12 is processed by the arithmetic unit 13 as follows.

The arithmetic unit 13 first calculates the peak value Inax of the scattered light pulse signal S from the data of the scattered light pulse signal S read out from the waveform storage device 12, as shown in FIG. Threshold levels are set at predetermined percentages for the value IIax, for example threshold levels of 90% and 10% for l1ax. Point x1 where the value of one scattered light pulse signal S intersects with the set threshold level. Find x2, and this
.

x2 is connected with a straight line, and the rise time Ow' of the scattered light pulse signal S is determined by extrapolation. Next, the determined rise time DI′ is the actual rise time D without extrapolation.
Because it is a small value compared to v.

In order to correct this and obtain the correct rise time Dw, we use the proportionality constant k, which has been determined experimentally in advance, and use the following formula to calculate OW.
Calculate.

DW = k x DW' (2) Next, a 50% threshold level is set for Inax, and the point X3. where the value of the scattered light pulse signal S intersects with the threshold level is set. Find X4.

This χ3. Calculate the time tv between X4. and.

The length Iz of the measurement field of view E, which is known in advance, and the above time 1v
From this, the passing velocity V of the particle M to be measured is calculated.

Next, using this passing speed ■ and the rise time Dw that has already been calculated, the measured particle M is determined according to equation 1(1).
Calculate the particle size. Then, the particle size of the particles M to be measured calculated as described above is displayed on the display device 14.

With the device configured in this way, the particle size of the particles M to be measured can be accurately determined for all cases where particles M to be measured or 1/2 or more of their size enter the measurement field of view E. This means that it can be measured. Therefore, reliability as a measuring device can be improved compared to conventional devices.

[Effect of the Invention 1] As described above, according to the present invention, the particle diameter is measured based on the rise time of the scattered light pulse signal obtained when the particle to be measured passes through the measurement field. The particle size can be accurately measured even when the particle to be measured passes through the edge of the measurement field of view.

The reliability of the device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the measurement principle of the particle size measuring device according to the present invention, FIG. 2 is a schematic configuration diagram of a particle size measuring device according to an embodiment, and FIG. 3 is an illustration of the actual measurement using the same device. A diagram for explaining the processing method, Figure 4 is a schematic configuration diagram of a conventional particle size measuring device, Figures 5 and 6 are diagrams for explaining the measurement principle in the same device, and Figure 7 is a diagram of the same device. FIG. 2 is a diagram for explaining the problem. A... Irradiation optical system, B... Light receiving optical system, C... Processing system. P...Measurement point, 1...Light source, 2.5.7...Lens, 3°9...Optical fiber, 4...Square waveguide, 6
···prism. 10... Photodetector, 11... Amplifier, 12... Waveform storage device, 13... Arithmetic device, 14... Display device. Appearing agent Patent attorney Takehiko Suzue t1t2t3t4 A Three times a month! l↑Mei Studies 1st move. Figure 3 A J1! fi Seven Light Palm Thread 4rM (a) Long □ (b) Figure 5 Demon Red Diameter <pm)

Claims (1)

[Claims] An irradiation optical system and a light receiving optical system that define a measurement field of view as a cube, and a size corresponding to the intensity of light guided through the light receiving optical system among the scattered light caused by the particles to be measured passing within the measurement field of view. A particle size measuring device comprising a photodetector that converts the particle size into an electric signal, and a particle size calculation means that calculates the particle size of the particle to be measured from the scattered light pulse signal output from the photodetector. A particle size measuring device characterized in that the diameter calculation means calculates the particle size from the rise time of the scattered light pulse signal.