Measurement Range

The range in which measurement by the laser diffraction/scattering method can be applied is several tens of nanometers extending up to the millimeter unit. However, note that actual numerical values for a laser diffraction particle size analyzer (i.e. particle size analyzer that operates based on the laser diffraction/scattering method) is dependent on the analyzer's optical system (wavelength of light source, location of diffracted/scattered light sensors, focal distance of condenser lens, etc.), as well as on the method used for sampling the measurement target (sample).

The numerical value for the measurement lower limit listed in catalogs and other literature, strictly speaking, is the distribution lower limit, and the measurement lower limit for 50 % diameter (median diameter) is larger than that. Alternatively, the numerical value for the measurement upper limit is the upper limit of distribution, and the measurement upper limit for 50 % diameter (median diameter) is smaller than that. Also, when a powder made up of solid particles is dispersed by compressed air and measured by dry measurement, about 1 µm is generally regarded to be the substantial lower limit because of the dispersibility limit.

In the case of wet measurement, the measurement upper limit is influenced not only by the optical system (wavelength of light source, location of diffracted/scattered light sensors, focal distance of condenser lens, etc.) but also by the circulation system of the sampler. So attention must be paid to particles having a high specific gravity. With some manufacturers and models, particle samples of about several hundred µm in size sometimes cannot be successfully measured even if the upper limit of the measurement range is over 1000 µm (1 mm). If the pump's circulating force is weak, large particles in the measurement target (sample) will be hard to circulate, and the particle size distribution will shift in the smaller direction since the amount of small particles will be overvalued, causing inaccurate measurement. I recommend actually trying out and testing pumps since the behavior of particles circulated by the pump cannot be assessed merely by the flowrate performance listed in catalogs.