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Particle measurement

The measurement and documentation of the particles is performed by digital image analysis. The system is validated before each measurement.

Particle parameters

In context of our digital analysis of the particles, the following parameters are determined:
  • Area
  • Shape factor (defines the deviation from a circle 0 < FF< 1; 1= Circle)
  • ECD (circle equivalent diameter)
  • Perimeter
  • Feret Max (maximum distance between two parallel tangents)
  • Feret Min (minimum distance between two parallel tangents)
  • Fiber length (= Perimeter / 2)

Typically, the Feret Max parameter classifies the size of a particle.

Influence of the container’s geometry on the measurement

Optic distortions can arise during the particle measurement because of the curved glass- and liquid (meniscus) surface. For measuring this purpose, certified glass spheres (with a diameter of 99,8 µm ± 1,8 µm) are transferred into the container. Once they sink to the bottom, they are measured. The ECD-, Feret Max and Feret Min values are then compared to one another.

Position of the object in the liquid

Digital image analysis shows a two dimensional picture of a three dimensional object (e.g. particle). The results therefore depend on the position of the particles in the respective formulation. The projected object lengths for objects 1 and 3 correspond to their true values. This is not the case for object 2 because of its sloping position it assumes. Therefore we ensure that the particle is lying in the lowermost zone of the formulation during the analysis.