JPH0368336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves sedimenting test particles uniformly dispersed in a medium solution under centrifugal force, detecting the particle concentration at a certain sedimentation distance, and determining the difference in sedimentation speed with respect to particle size. This invention relates to an apparatus for determining the particle size distribution of sample particles.

Generally, when particles are uniformly dispersed in a medium solution and a centrifugal force is applied to them, the particles settle in the direction of the centrifugal force. When ω is the particle density, ρp is the density of the medium, ρl is the particle diameter, Dp is the particle diameter, and η is the viscosity of the medium, v=Rω ² (ρp−ρl)Dp ² /18η (1). As is clear from this formula, the particle size
The larger Dp is, the faster the particles will settle. When a test sample consisting of various particles is uniformly dispersed in a medium solution and sedimented in a centrifugal force field, each particle sediments at a speed according to the particle size according to equation (1), and a certain amount of sedimentation is achieved. Measure the concentration in this medium solution over time at the distance, and measure the time t on the time axis corresponding to each measurement point, that is, the time t from the start of applying centrifugal force to each measurement time, (1) can be modified and integrated over the distance R to obtain t={1.05η/N ² (ρp−ρl)}・log
(R ₂ /R ₁ )・1/Dp ² ...(2) where N: Number of revolutions per unit time (1 second) R ₁ ; Distance between center of rotation and medium solution surface R ₂ ; Center of rotation and concentration measurement point By converting the time t on the time axis corresponding to each measurement point into particle diameter Dp by the distance from have been determined, and the particle size distribution can be calculated from these.

Conventionally, in devices that measure particle size distribution using this type of method, the rotational speed of the centrifuge to apply centrifugal force to the sample particles in the medium solution is kept constant throughout one measurement cycle. was. When measuring the particle size distribution of test particles consisting of particles of various sizes using this conventional device, if the rotation speed of the centrifuge is set to a high speed, particles with small particle sizes will settle quickly and settle in a short time. The measurement is completed, but particles with large diameters settle too quickly and cannot be measured, and in order to measure them, the upper limit of the rotational speed of the centrifugal force is automatically determined. Therefore, it has the disadvantage that it takes a considerable amount of time for particles with small diameters to settle at the concentration measurement point and to complete the measurement.

The present invention has been made to solve the above-mentioned drawbacks, and is a particle size distribution measuring device that can accurately measure the distribution of particles with large particle diameters and can also measure small particle diameters in a short time. The purpose is to provide.

In the particle size distribution measuring device of the present invention, the rotational angular velocity ω of the centrifuge for applying centrifugal force to the sample particles in the medium is determined by a preset monotonically increasing function ω=f
It is configured to perform acceleration control according to (t) and to convert the momentary concentration detection results in this state into particle size distribution based on the following formula.

d ² R／dt ² = Rω ² (ρ _p −ρ _l /ρ _p )−18η／ρ _p・D _p ²
・dR/dt where R is the distance from the center of rotation to the particle, ρ _p
is the particle density, ρ _l is the density of the medium, D _p is the particle diameter, η
is the viscosity coefficient of the medium, t is time, and ω is ω=f(t) as described above.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention.

A sedimentation container 1 for sealing sample particles uniformly dispersed in a medium solution is attached to a rotating disk 3 attached to a rotating shaft of a motor 2. The concentration of the medium solution in the sedimentation container 1 is detected by using a concentration detection light source 4 that is installed at a certain distance from the center of rotation and emits light that crosses the rotating sedimentation container 1, and receives the light and converts it into an electrical quantity. The output of the light receiving section 5 is sent to the central processing unit 8 via the A/D converter 6 and the input/output device 7.
The output of a timer 9 for measuring the elapsed measurement time is also introduced into the central processing unit 8 via the input/output device 7, and the concentration detection value at each time point and the elapsed measurement time corresponding to each time point are used to calculate the output value, which will be described later. Calculate the particle size distribution. This measurement program and calculation program are stored in the read-on memory 10,
Further, each concentration detection value, particle size distribution calculation result, etc. are configured to be stored in the random access memory 11.

On the other hand, the motor 2 that drives the rotating disk 3 is a DC motor whose rotational speed can be changed according to the supplied voltage, and is connected to a voltage control circuit 12 . The rotating disk 3 has small holes equally spaced on the circumference around the center of rotation, a light source 13 for detecting rotational speed that emits light that crosses the small holes, and a light receiver for detecting rotational speed that receives the light. A rotation speed detection circuit 15 is provided which detects the rotation speed of the rotary disk 3 by introducing the output of the light receiving section 14 and the rotation speed detection circuit 15, and this rotation speed detection value is supplied to a comparison circuit 16. Comparison circuit 16
Also, the output of a reference signal generation circuit 17 that generates a reference signal according to a monotonically increasing function regarding the elapsed time of the rotational speed shown in FIG. 2 is introduced, and the difference signal is supplied to the voltage control circuit 12 described above. Motor 2
is controlled by feedback. This reference signal generation circuit 17 is connected to a central processing unit 8 via an input/output device 7, and the central processing unit 8 takes in the measurement elapsed time from a timer 9, and stores it in advance in a read-on memory 10. The output of the reference signal generating circuit 17 is controlled in accordance with a function of rotational speed over time as shown in FIG.

The method of calculating the particle size distribution using the concentration detection value at each point and the elapsed measurement time corresponding to each point is the same as the calculation method of conventional equipment, but the time axis corresponding to each concentration measurement point is Since the rotation speed of the rotating disk 3 changes based on a function of the elapsed measurement time, the above equation (2) for converting t into the particle length Dp is changed as follows.

d ² R／dt ² =Rω ² (ρp−ρl／ρp)−18η／ρp・Dp ²
・dR/dt...(3) Here, R is the distance from the center of rotation to the point where the particle exists, and ω is a function of time such that ω=f(t),
For example, in the region from t=o to t= _t1 in Figure 2, it is expressed by the equation ω=at, which can be substituted into equation (3), which is a variable coefficient type second-order differential. Since it is an equation, it can be solved for the distance R,
The relationship between distance R and time t can be confirmed for each particle diameter Dp. Therefore, the solution to this differential equation may be stored in the read-only memory 10 and the particle diameter Dp may be determined from the time t by the central processing unit 8. Alternatively, the particle diameter Dp corresponding to each time t may be stored in advance in a read-only memory.

Equation (3) has the following meaning. In other words, considering the equation of motion of a particle in a centrifugal field, we get the following
Equation (4) is obtained.

π/6D _P ³ ρ _p d ² R/dt ² = π/6D _p ³ (
ρ _p −ρ _l ) Rω ² −3πηD _p dR/dt...(4) The left side of equation (4) is the net force acting on the particle, which is in the form of mass x acceleration. Further, the first term on the right side is a term indicating the difference between gravity and buoyancy acting on the particle, and the second term on the same side is a term indicating the resistance force that the particle receives from the fluid when the particle moves.

By rearranging and eliminating the common terms in equation (4), equation (3) is obtained. Therefore, equation (3) is used to comprehensively capture particle motion and obtain particle diameter from actual particle motion. It can be said that the formula is

It goes without saying that the function related to the elapsed time of the rotational speed in the above embodiment may be a linear function as shown in FIG. 2, or may be another continuous monotonically increasing function. Further, the rotary disk drive motor and voltage control circuit may be other known variable speed motors and their control circuits, and furthermore, other known means may be used as the rotational speed detection means of the motor. Needless to say.

As explained above, according to the present invention, since centrifugal force is small at a point where the rotational speed is low immediately after the application of centrifugal force starts, particles with large particle diameters settle at a relatively low speed, and the sedimentation can be detected. can be easily and accurately measured, as the rotational speed increases over time, and by the time particles with a small diameter settle, the centrifugal force has increased, so the sedimentation rate increases and the rotation speed increases over a short period of time. The measurement can be completed in a few seconds.

Moreover, even if the rotational speed of the centrifuge is changed to increase temporarily during the measurement, this change is accurately reflected in the calculation of the particle size distribution, so the error caused by the change in the control method of the centrifuge is reduced. Therefore, according to the present invention, particle size distribution can be measured accurately in a short time. In addition, since the rotational speed of the motor is not accelerated to a constant rotational speed all at once as in conventional devices, but is accelerated gradually, the startup time of the motor is shortened, and measurement errors caused by ignoring the startup time are reduced. It decreased, and the disturbance of the sedimentation system also became less. Furthermore, since it is possible to know the motor rotation speed immediately after the rotation starts,
It became possible to track the movement of particles throughout the entire sedimentation region.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between measurement elapsed time and rotational speed. DESCRIPTION OF SYMBOLS 1... Sedimentation container, 2... Motor, 3... Rotating disk, 4... Light source for concentration detection, 5... Light receiving section for concentration detection, 8... Central processing unit, 12... Voltage control circuit, 13... ... light source for rotational speed detection, 14 ... light receiving section for rotational speed detection, 15 ... rotational speed detection circuit,
16... Comparison circuit, 17... Reference signal generation circuit.

Claims (1)

[Claims] 1. Sample particles uniformly dispersed in a medium are allowed to settle under the centrifugal force of a centrifuge, and the concentration is detected at a certain settling distance, and the sedimentation rate according to the particle size is determined. In an apparatus equipped with a conversion means that utilizes the difference to convert the instantaneous concentration detection results into the particle size distribution of the sample particles, the rotational angular velocity ω of the centrifuge is adjusted to a monotonically increasing time function ω set in advance. =f(t)
A particle size distribution measuring device controlled according to the following, and wherein the conversion means is configured to convert the function ω and the concentration detection result into a particle size distribution based on the following formula. d ² R／dt ² = Rω ² (ρ _p −ρ _l /ρ _p )−18η／ρ _p・D _p ²
・dR/dt Where, R: Distance from the rotation center to the particle ρ _p ; Particle density ρ _l ; Medium density D _p ; Particle diameter η ; Viscosity coefficient of the medium t : Time