JP3431777B2 - Particle size distribution analyzer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a cell containing a sample with light from a light source, and detects scattered light at that time with a plurality of photodetectors. The present invention also relates to a particle size distribution measuring device for measuring a particle size distribution in a sample based on a scattered light intensity signal from each photodetector. 2. Description of the Related Art FIG. 4 shows a main part of a conventional particle size distribution measuring apparatus by a laser diffraction / scattering method. In this figure, reference numeral 1 denotes a laser tube which emits a He--Ne laser beam 2; Is a beam expander for appropriately expanding the laser beam 2, 4 is a cell for accommodating the sample 5, 6 is a condenser lens provided behind the cell 4, and 7 is a plurality of photodiodes provided behind the condenser lens 6. A ring detector in which the photodetectors 7a to 7n are arranged in a ring shape; 8a to 8n are amplifiers provided corresponding to the plurality of photodetectors 7a to 7n; A multiplexer for sequentially taking in the output signals of 7a to 7n; 10, an A / D converter;
Is a photodetector 7a sequentially input through the A / D converter 10.
Is a CPU for performing calculations based on scattered light intensity signals from .about.7n to obtain a particle size distribution. In the scattering type particle size distribution measuring device,
When the sample 5 is stored in the cell 4 and the laser beam 2 is irradiated to the cell 4, a part of the laser beam 2 irradiates the particles 12 in the sample 5 in the cell 4 to become forward scattered light 13, Light passes between the particles 12 and becomes the transmitted light 14. Then, both the forward scattered light 13 and the transmitted light 14 reach the photodetectors 7a to 7n via the condenser lens 6. [0004] The above-mentioned scattering particle size distribution measuring apparatus requires a large number of diffracted light intensity signals and scattered light intensity signals due to the principle of measurement. Is provided with a ring detector 7 in which a plurality of photodetectors 7a to 7n are arranged in a ring shape, but conventionally, an amplifier 8 is provided corresponding to each of the photodetectors 7a to 7n.
a to 8n are provided, and the signals amplified and processed for each of the channels 15a to 15n corresponding to each of the photodetectors 7a to 7n are sequentially sent to one A / D converter 10 via the multiplexer 9, and the A / D converter 10 In each of the photodetectors 7a to 7n
Are individually A / D converted and output to the CPU 11, so that the signal processing is complicated,
Therefore, there is a problem that processing time is required. [0005] In recent years, this type of particle size distribution measuring apparatus has been required to measure small particles, particularly fine particles of 0.1 µm or less. It is difficult to calculate the particle size distribution using only forward scattered light, and the wavelength of side / backward scattered light, polarized scattered light, and He-Ne laser light (632.8 nm).
Information such as scattered light when irradiating light with a shorter wavelength is also required. [0006] Therefore, in the particle size distribution measuring device, a large number of photodetectors are provided for detecting the various kinds of scattered light, and the number of channels is increasing in order to improve the resolution. As described above, in the particle size distribution measuring device provided with many photodetectors, in the above-described conventional signal processing method, the signal sent through the multiplexer 9 is sequentially A / D converted by the A / D converter 10. Since the converted output is sent to the CPU 11, it becomes difficult to perform signal processing efficiently in a short time. The present invention has been made in consideration of the above-mentioned matters, and has as its object to simplify the signal processing system as much as possible and to increase the number of photodetectors (the number of channels). Another object of the present invention is to provide a particle size distribution measuring device capable of efficiently performing signal processing in a short time. In order to achieve the above object, according to the present invention, a cell containing a sample is irradiated with light from a light source, and scattered light at that time is supplied to a plurality of photodetectors. In the particle size distribution measuring device that detects in the, and measures the particle size distribution in the sample based on the scattered light intensity signal from each photodetector,
The outputs of the photodetectors are modulated at mutually different frequencies, the modulated signals are added, and the added signal is A / D-converted and then Fourier-transformed. According to the particle size distribution measuring device having the above-described structure,
Since the signal input to the A / D converter is one signal obtained by adding the outputs of a large number of photodetectors, signal processing can be performed easily, and signal processing can be performed efficiently in a short time. it can. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. In the following drawings, the same reference numerals as those shown in FIG. 4 indicate the same components. FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 shows the structure of a particle size distribution measuring apparatus according to the present invention after a photodetector, and FIG. . In FIG. 1, reference numerals 16a to 16n denote channels 15a to 15n having a plurality of photodetectors 7a to 7n.
Are frequency modulators provided respectively. These frequency modulators 16a to 16n frequency-modulate the outputs of the photodetectors 7a to 7n sent through the amplifiers 81 to 8n, and have different modulation frequencies in the respective channels 15a to 15n. In this embodiment, the frequency modulators 16a to 16n also have a function of converting the modulated signal from a voltage signal to a current signal. Reference numeral 17 denotes an adder for adding the modulation outputs outputted in the form of current signals from the frequency modulators 16a to 16n. The addition output from the adder 1 is sent to the A / D converter 10. In this embodiment, the CPU 1
1 is a fast Fourier transform (FF) of the output of the A / D converter 10.
FT). Next, the signal processing operation in the particle size distribution measuring apparatus having the above configuration will be described with reference to FIG. Photodetectors 7a to 7n of each channel 15a to 15n
Are amplified by the amplifiers 8a to 8n and input to the frequency modulators 16a to 16n. The signals from the photodetectors 7a to 7n input to the frequency modulators 16a to 16n are modulated at different frequencies for each channel. FIG. 2 shows channels a to a for convenience of explanation.
3C shows the processing states of the signals S _a , S _b , and S _c in the three cases c.
The output signals S _a , S _b , S _c of _{a to} 7c are respectively modulated at different frequencies ω _a , ω _b , ω _c . After the frequency modulation, the signals S _a , S _b , and S _c are converted from voltage signals to current signals. The reason why the voltage signal is converted to the current signal is that the addition of the current signals can be performed more easily. The modulated outputs S _a , converted into the current signals,
S _b and S _c are added together in an adder 17 to form one signal. This signal is A / D-converted by the A / D converter 10 and then input to the CPU 11, where
The PU 11 performs the FFT processing. This FFT processing, as shown at the right end in FIG. 2, the frequency omega _a,
Spike frequency spectra are obtained at the positions of ω _b and ω _c , respectively. The magnitude (length in the vertical direction) of this spectrum is determined by the output signals S _a , S _b , and S _{c of the} photodetectors 7a to 7c.
It is itself. The CPU 11 performs a predetermined process based on the output signals S _a , S _b , and S _c, that is, the scattered light intensity signal. As described above, according to the particle size distribution measuring device, the signal input to the A / D converter 10 is one signal obtained by adding the outputs of the many photodetectors 7a to 7n. The signal processing can be easily performed, and the signal processing can be efficiently performed in a short time. FIG. 3 shows another embodiment of the present invention. In this embodiment, the photodetectors 7a to 7n and C
The PU 11 side is wirelessly connected. That is, in FIG. 3, reference numeral 18 denotes a wireless communication transmitting unit provided on the output side of the adder 17, which internally includes an A / D converter for A / D converting the output of the adder 17, a CPU, a high-frequency transmitting unit, , And an external antenna 18a. Reference numeral 19 denotes a wireless communication receiving unit provided on the input side of the CPU 11, which is internally provided with a high-frequency transmitting unit, a CPU, and a power supply unit thereof, and externally provided with an antenna 19a. In such a particle size distribution measuring device, the output of the adder 17 is A / D converted and then transmitted wirelessly from the wireless transmission unit 18, and the transmitted signal is
After being received by the wireless receiving unit 19, the scattered light intensity signal is obtained by being input to the CPU 11 and processed in the same manner as in the above embodiment. In each of the embodiments described above, the output of the adder 17 is subjected to the FFT processing in the CPU 11, but may be processed by other Fourier transform. The present invention is embodied in the form described above and has the following effects. In the particle size distribution measuring device of the present invention,
The outputs of the plurality of photodetectors are modulated at mutually different frequencies, the respective modulated signals are added, and the signals resulting from the addition are A / D-converted and then Fourier-transformed. Becomes as simple as possible, and even if the number of photodetectors (the number of channels) increases, signal processing can be performed efficiently in a short time. Also, since a single signal is transmitted,
Wireless communication can be performed, and signal transmission between the measurement unit and the signal processing unit in the particle size distribution measurement device can be made wireless.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of a configuration for processing a signal of a photodetector in a particle size distribution measuring device of the present invention. FIG. 2 is a diagram for explaining the operation of the configuration. FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 4 is a diagram for explaining a conventional technique. [Description of Signs] 1 ... light source, 2 ... light, 4 ... cell, 5 ... sample, 7a-7n ...
Photodetector, 11 CPU, 13 Scattered light, 16a to 16
n: frequency modulator, 17: adder.

Claims (1)

(57) [Claims 1] A cell containing a sample is irradiated with light from a light source, and scattered light at that time is detected by a plurality of photodetectors. In the particle size distribution measuring device for measuring the particle size distribution in the sample based on the scattered light intensity signal, the outputs of the respective photodetectors are modulated at mutually different frequencies, the modulated signals are added, and the addition is performed. Signal from A
A particle size distribution measuring device characterized by performing a Fourier transform after performing a / D conversion.