Problems in selecting light shading rate during laser particle size analyzer testing

The shading rate is the concentration of the sample suspension configured when using a laser particle size analyzer to test samples. The correct selection of the shading rate is an important step in the particle size testing process of the laser particle size analyzer. Whether the shading rate is appropriate or the sample being tested is Whether the concentration is appropriate is closely related to the accuracy and representativeness of the particle size measurement results.

The measurement principle of the laser particle size analyzer requires that during the test process, the concentration of the sample is based on the principle that the particles in the sample do not scatter each other twice. Theoretically, the distance between particles in the suspension or air is required to be 3 times the particle diameter. , but this requirement is very difficult to master, so in the actual particle size test, the value of the shading rate is adjusted to try to ensure that no secondary scattering occurs between particles. The shading rate should not be too large (more than 50%) or too small (less than 5%). When the shading rate is too large, the concentration of particles is too high, and secondary scattering is prone to occur, which increases the error of the measurement results; when the shading rate is too low, the sample If the concentration of particles in the medium is too low and the number of particles is too small, the representativeness of the test results is very poor, and may even cause the test results to be invalid. Therefore, during the test process, the selection of the shading rate must be conducted through repeated trials to obtain correct measurements. result.

The specific calculation method is to divide the difference between the light intensity I0 at the center point of the detector after the laser passes through the pure medium and the light intensity Ii at the center point of the detector after adding the sample divided by the light intensity I0, that is, the shading rate =（I₀—I_i）/I₀ x 100%，

   Generally speaking, for relatively thick samples, the shading rate can be selected to be relatively high, such as 20~30%, and the normal situation can be 10~25%; for ultra-fine samples, the shading rate of the sample can be appropriately reduced, but generally not More than 40%, these are empirical values obtained from experiments, but in the end it is necessary to find the optimal value for the shading rate corresponding to the sample test through repeated experiments.