During particle sizing, the relative value of shading rate is used to represent the concentration of suspension. The shading rate is determined by the number of particles in the suspension: the more particles in the suspension, the stronger the scattered light, the higher the shading rate; the fewer particles in the suspension, the weaker the scattered light, and the lower the shading rate. In order to achieve a certain shading rate, more particles are required for coarse particles whilst a smaller amount of particles are needed for fine particles. Thus, the percentage concentration is higher for suspensions of coarse particles and it is lower for finer particle suspensions.
In addition, even if the particle size is the same, the percentage concentrations may still be different because their densities are different.
Therefore, the percentage concentrations should not be fixed in laser particle sizing. Instead, the shading rate, a relative value, is used. The percentage concentration can only be a range, which is usually 0.01% - 0.1%.