Model 11-R
GRIMM AEROSOL TECHNIK GmbH & Co.KG Seite 40 von 83
Figure 3-2: Schematic of the laser measuring chamber
The count rate is derived from the number of particles divided by the volume flow rate. The particle size
is proportional to the intensity of the detected scattered light signal. In addition to the particle size, the
scattered light intensity is also influenced by the refraction index of the particle form and the orientation
of the particle in the sensing volume. Positioning the detector in the 90° direction makes it possible to
minimise the influence of the refraction index for the aerosol particles on the determination of the parti-
cle size. The large opening angle of the detector optics was chosen so that ambiguities in the scattered
light intensity are compensated by resonances, which inevitably occur when monochromatic laser light
is used.
This makes the clear assignment of the particle size to sufficiently narrow size classes possible. The 11-
R uses 31 size channels. Capturing the particle concentration and particle size makes it possible to
capture the size distribution of the aerosol particles, which in turn is the foundation for calculating the
particle mass.
volume
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