Residual dirt analyses for counting particles

Residual dirt analysis is carried out by inspecting samples of product and packaging for residual dirt particles. Those particles can be both product parts respectively abrasion such as rubber or plastic particles, as well as fibers or human tissue.

During sample preparation, the product is rinsed with highly cleaned water, which is then filtered on a paper filter with a pore size of 0.8 micrometers. The dirt particles remain on the filter membrane, which is stored in a petrislide made of plastic and then closed with a transparent lid.

The sample, with the lid closed, is illuminated using a combination of red dark-field lighting and white top-light.

An ultra-high resolution camera (16 megapixels) is used to record image sequences with a controlled illumination.

Particles with a size of 15 micrometers and larger are detected.  Particles with a size of 25 micrometers and larger are classified. A difference is made between fibers and other particles.