The APMON sensor collects the deposited particles on inclined glass witness plates in the cartridge. Particles stick to the position where they landed due to Van der Waals forces. By taking regular pictures of these witness plates the additional particles can be measured. Holographic imaging makes it possible to do this for all witness plates in one three-dimensional picture.
Holographic Measurement Method: Coherent laser beams that pass the surface of a particle are mixed with undisturbed laser beams and detected.
- The recorded image shows a diffraction pattern from which using Fourier transformation methods the change of the real image can be reconstructed.
- The result is the particle size distribution of the particles that are deposited since the previous measurement (5 minutes before).
- Particles deposit on glass plates under an angle of 45O.
- Broad coherent light beam passes these glass plates.
- Sensor detects interference pattern generated by the deposited particles.
- This pattern contains information on the number of particles, their size and shape.
- Each interval the change in this pattern is measured to determine the deposition of particles.