## 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.