Understanding the Technical Background

Component Cleanliness Analysis is usually not only focused on particle counting results, but also on the differentiation by particle type.

Using a microscope, the established analysis is performed by sequential acquisition of two images. One image is recorded with the parallel orientation of two polarizer and a further image is recorded with the two polarizer in 90° orientation to each other (crossed polarization).

Metallic particles appear dark black when using crossed polarization whereas non-metallic particles often change their appearance from gray to darker gray or even do not show any reaction on polarization. This effect is used to differentiate between metallic-shiny and non-shiny particles.

The new camera technology with on-chip polarization allows parallel acquisition of one dual channel image with both directions of polarization at the same time. This leads to time reduction by 100% for the image acquisition step.

This functionality is only available when using the Axiocam 705 pol.

The component cleanliness job templates are designed to analyze images acquired with the Axiocam 705 pol.

See also

• Applying Polarization Channel

The POL camera is a black and white camera and offers beside the raw image four selectable directions of polarization: 0°, 45°, 90°, 135° to acquire a multi-channel image. The raw image shows all directions of polarization. In color mode the images are displayed in false-color.

After image acquisition, the selected directions of polarization are extracted from the raw image and provided as multi-channel image.

The default value for multi-channel images shall be Single Channel. This is valid for all TCA job templates.

If single channel is not activated, the merged image is displayed. The merged image is an additive image of all selected channels and therefore much brighter than the single channel images.

1. Axiocam 705 pol is installed.
2. In the Extended Camera tool > Mode section, the camera mode B/W is selected.
3. In the Extended Camera tool > Mode section, Live speed high is selected.
4. In the Extended Camera tool > Model Specific section, the channels 90° and 135° are selected.
5. On the Display tab, Single Channel is activated. It is not possible to display more than one channel at the same time. You can switch between the two image channels to differentiate immediately between metallic and non-metallic particles. The Pol-90° channel and one additional channel, i.e. 0°, 45° 135° is mandatory for correct differentiation of the particle types metallic-shiny and non-shiny.

1. To display metallic particles bright shining, in the Image View, on the Display tab, select Pol-135 channel. Note: Depending on the particle surface and its orientation on the filter membrane, it might be that only smaller areas of the metallic particle appear bright shining. This is a general effect using polarization and is independent of the applied technology.
   Note: Also, the 0° or the 45° channel can be selected to display metallic particles bright shining, but it is recommended to use the 135° channel. In this setting, metallic particles are not outshined which leads to a better image quality in the report. Furthermore, foamed filter membranes show less reflections.
2. In the image, the metallic particle is displayed in Pol-135 channel.
   
2. To display metallic particles dark black, in the Image View, on the Display tab, select Pol-90.
3. In the image, the metallic particle is displayed in Pol-90 channel.
   

Example: Non-metallic particle

Non-metallic particles do not react on polarization with a change in brightness from silver white to dark black. In most of the cases you can observe a change from gray to darker gray, even for those materials with reflecting brighter areas. They never get dark black when using crossed polarization.

The Relative Image Brightness (Luminosity) is adjusted to 55% which means that the filter background indicated by the largest peak (gray value with the highest intensity in pixel counts) appears in the middle of the gray value range:

The Relative Threshold is set at 70% referring to the Relative Image Brightness (Luminosity) setting.

For information on setting the relative image brightness (Luminosity), see Camera Tool and Light Path Editing Tool.

For information on relative threshold, see Particle Segmentation Tool (Components).