The laser particle size analyzer mainly consists of an optical detection system, a decentralized sample introduction system, and a control analysis software. The optical detection system also includes key parts such as a light source, an optical path, and a detector. When selecting a laser particle size analyzer, pay special attention to the following points:
1. There are two kinds of light sources: helium gas laser and semiconductor solid-state laser. The helium laser has narrow line width and excellent monochromaticity. It is not affected by the fluctuation of power supply voltage and temperature change, and has high stability, especially in recent years. With the development of such technologies, the service life has been greatly improved. Therefore, although holmium lasers have the disadvantages of large size, high voltage power supply and high price, they are still used by some high-end instruments. Semiconductor lasers have the advantages of small size, low supply voltage, long service life, and low price compared to HeNe lasers. However, they have poor monochromatism, wide line width, and are susceptible to changes in temperature and power supply fluctuations. The shortcomings also limit its application in the instrument. Of course, it is foreseeable that with the improvement of semiconductor light source technology, semiconductor solid-state lasers will be used more in particle size analyzers. In addition, it should be noted that the effect of laser wavelength on particle size measurement is that when the particles are small, according to Rayleigh scattering theory, the scattered light intensity is proportional to the sixth power of the particle size and inversely proportional to the fourth power of the wavelength of the light source. The use of short-wavelength lasers can improve the signal intensity and signal-to-noise ratio of small particles.
2, in the light path configuration, mentioned in front of the above, the main need to consider is whether the instrument has a stable optical platform, whether there is automatic light function, whether you need to change the lens can measure a wide range of particle size; if needed According to the method, whether the lower limit of the particle size measurement range can reach 0.1 micrometers and the upper limit can reach more than 1000 micrometers at the same time.
3. The detector is one of the most critical components of the laser particle size analyzer. The cost of a good detector sometimes accounts for more than one-fourth of the cost of the entire particle size analyzer. The detector is specifically mentioned in the ISO 13320 laser diffraction method international standard section 6.7. The influence on the sensitivity and resolution of the instrument, so when choosing can not only consider the number of detection units in the detector, but also to see the detector geometry, arrangement, detection unit area and its real physical detection angle.
4. The sample dispersion sample introduction system is an important accessory to ensure that the sample is properly dispersed and sampled. The wet dispersion sampler needs a circulating pump with built-in ultrasonic and stirring and sufficient strength. It is best to use a centrifugal pump. The dry-dispersing sampler needs With the vibration sample function, the pressure of the air flow can be adjusted, and sample trays with different capacities are available. In addition, the sample sometimes inevitably adheres to the window of the sample cell during sample measurement, so it is also very important whether the sample cell is easily disassembled and cleaned.
5, software is used for instrument control and data analysis, the faster the data collection, the better. In the ISO 13320 international standard, it is particularly proposed that if the particle size is less than tens of micrometers, Mie theory must be used to input the correct refractive index and absorption rate of the sample so that more accurate results can be obtained. Therefore, a general substance is required in the software. The optical parameters, ie the refractive index and the absorption rate database, can supplement the input of these optical parameters. In addition, data output functions, user report format design functions, and range expansion functions are also indispensable factors. If there are Chinese software and Chinese manuals, it will be a good choice for most Chinese users.
6. The last point to mention is the accuracy, reproducibility, or accuracy of the laser particle size analyzer measurements. These indicators should be for certain characteristics of standard samples (such as NIST traceable latex particles) (eg, D50, D10, D90, etc.) If only 0.5% or less is marked on the instrument sample without specifying the specificity, it will inevitably mislead the user. Therefore, when the user sees these indicators, it is necessary to confirm its specificity and specificity. meaning.
1. There are two kinds of light sources: helium gas laser and semiconductor solid-state laser. The helium laser has narrow line width and excellent monochromaticity. It is not affected by the fluctuation of power supply voltage and temperature change, and has high stability, especially in recent years. With the development of such technologies, the service life has been greatly improved. Therefore, although holmium lasers have the disadvantages of large size, high voltage power supply and high price, they are still used by some high-end instruments. Semiconductor lasers have the advantages of small size, low supply voltage, long service life, and low price compared to HeNe lasers. However, they have poor monochromatism, wide line width, and are susceptible to changes in temperature and power supply fluctuations. The shortcomings also limit its application in the instrument. Of course, it is foreseeable that with the improvement of semiconductor light source technology, semiconductor solid-state lasers will be used more in particle size analyzers. In addition, it should be noted that the effect of laser wavelength on particle size measurement is that when the particles are small, according to Rayleigh scattering theory, the scattered light intensity is proportional to the sixth power of the particle size and inversely proportional to the fourth power of the wavelength of the light source. The use of short-wavelength lasers can improve the signal intensity and signal-to-noise ratio of small particles.
2, in the light path configuration, mentioned in front of the above, the main need to consider is whether the instrument has a stable optical platform, whether there is automatic light function, whether you need to change the lens can measure a wide range of particle size; if needed According to the method, whether the lower limit of the particle size measurement range can reach 0.1 micrometers and the upper limit can reach more than 1000 micrometers at the same time.
3. The detector is one of the most critical components of the laser particle size analyzer. The cost of a good detector sometimes accounts for more than one-fourth of the cost of the entire particle size analyzer. The detector is specifically mentioned in the ISO 13320 laser diffraction method international standard section 6.7. The influence on the sensitivity and resolution of the instrument, so when choosing can not only consider the number of detection units in the detector, but also to see the detector geometry, arrangement, detection unit area and its real physical detection angle.
4. The sample dispersion sample introduction system is an important accessory to ensure that the sample is properly dispersed and sampled. The wet dispersion sampler needs a circulating pump with built-in ultrasonic and stirring and sufficient strength. It is best to use a centrifugal pump. The dry-dispersing sampler needs With the vibration sample function, the pressure of the air flow can be adjusted, and sample trays with different capacities are available. In addition, the sample sometimes inevitably adheres to the window of the sample cell during sample measurement, so it is also very important whether the sample cell is easily disassembled and cleaned.
5, software is used for instrument control and data analysis, the faster the data collection, the better. In the ISO 13320 international standard, it is particularly proposed that if the particle size is less than tens of micrometers, Mie theory must be used to input the correct refractive index and absorption rate of the sample so that more accurate results can be obtained. Therefore, a general substance is required in the software. The optical parameters, ie the refractive index and the absorption rate database, can supplement the input of these optical parameters. In addition, data output functions, user report format design functions, and range expansion functions are also indispensable factors. If there are Chinese software and Chinese manuals, it will be a good choice for most Chinese users.
6. The last point to mention is the accuracy, reproducibility, or accuracy of the laser particle size analyzer measurements. These indicators should be for certain characteristics of standard samples (such as NIST traceable latex particles) (eg, D50, D10, D90, etc.) If only 0.5% or less is marked on the instrument sample without specifying the specificity, it will inevitably mislead the user. Therefore, when the user sees these indicators, it is necessary to confirm its specificity and specificity. meaning.
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