Selection of laser particle size analyzer

Selection of laser particle size analyzer

　　

The laser particle size analyzer mainly consists of an optical detection system, a dispersed sampling system, and control analysis software, and the optical detection system includes key parts such as the light source, optical path, and detector. When choosing a laser particle size analyzer, special attention should be paid to the following points:

　　

1. Light source

　　

There are mainly two types of light sources: helium neon gas lasers and semiconductor solid-state lasers. Helium neon laser instruments have narrow wires, monochromaticity, are not affected by power supply voltage fluctuations and temperature changes, and have high stability. Especially in recent years, the development of sealing and other technologies has greatly improved their service life. Therefore, although helium neon lasers have the disadvantages of large volume, high voltage power supply, and high price, they are still used by some instruments. Semiconductor lasers have the advantages of small size, low power supply voltage, long service life, and lower price compared to helium neon lasers. However, their poor monochromaticity, wide linewidth, and susceptibility to temperature changes and power supply fluctuations also limit their application in instruments. Of course, it can be foreseen that with the improvement of semiconductor light source technology, semiconductor solid-state lasers will be more used in particle size analyzers. Additionally, it should be noted that the wavelength of the laser has an impact on particle size measurement. According to Rayleigh scattering theory, when the particle size is small, the scattered light intensity is proportional to the sixth power of the particle size and inversely proportional to the fourth power of the light source wavelength. Therefore, using a short wavelength laser can better improve the signal strength and signal-to-noise ratio during small particle detection.

　　

2. In terms of optical path configuration, as mentioned earlier, the main considerations are whether the instrument has a stable optical platform, whether it has automatic alignment function, and whether it can measure a wide range of particle sizes without replacing the lens; If dry measurement is required, can the lower limit of particle size measurement range reach 0.1 microns while the upper limit can reach over 1000 microns.

　　

3. The detector is one of the most critical components of a laser particle size analyzer, and the cost of a good detector can sometimes account for more than a quarter of the total cost of the particle size analyzer. In section 6.7 of the ISO13320 laser diffraction standard, it is specifically mentioned that the detector has an impact on the sensitivity and resolution of the instrument. Therefore, when selecting, one cannot only consider the number of detection units in the detector, but also the geometric shape, arrangement, area of the detection units, and their true physical detection angle.

　　

4. The sample dispersion and injection system is an important accessory to ensure the correct dispersion and injection of samples. Wet dispersion and injection devices require built-in ultrasound and stirring, as well as a centrifugal pump with sufficient power circulation. Dry dispersion and injection devices require vibration injection function, adjustable airflow pressure, and sample trays of different capacities to choose from. In addition, during the sample measurement process, the sample may inevitably adhere to the window of the sample cell, so whether the sample cell is easy to disassemble and clean is also very important.

　　

5. Software is used for instrument control and data analysis, and the faster the data acquisition speed, the better. In the ISO13320 standard, it is specifically stated that if the particle size is less than tens of micrometers, the Mie theory should be used to input the correct refractive index and absorption index of the sample in order to obtain more accurate results. Therefore, the software needs to have a database of general material optical parameters, namely refractive index and absorption index, and be able to supplement the input of these optical parameters. In addition, data output function, user report format design function, range expansion function, etc. are also factors of *. If there were Chinese software and manuals, it would be a better choice for most Chinese users.