BSA Flow Software Installation and User's Guide - CSI

The trajectory effect
The slit effect
The trajectory effect can be attributed to the non-uniform (Gaussian)
intensity distribution in the measurement volume, as is illustrated in Figure
7-26. In this figure the measurement volume is defined by the receiving
optics placed at an angle to receive light scattered by first order refraction.
As indicated in this figure, there exist particle positions within the volume
(trajectories) where reflection may become the dominant scattering mode
due to the much higher intensity of the incident light, in particular on the
negative Y-axis. In such cases the unwanted, reflectively scattered light
contribution will be processed with the refraction-based phase-diameter
relation and therefore lead to incorrect size information.
Intensity
Projeced slit
Intersection volume
Y Y
Figure 7-26: The trajectory effect expressed in terms of geometrical optics.
From this representation of the trajectory effect, it is evident that only
droplets large relative to the dimensions of the beam waist can be affected.
However in dense sprays, it is desirable to drastically decrease the
measurement volume dimensions for two reasons; to increase the light
intensity and to decrease the probability of multiple particles being in the
volume simultaneous. Thus, the trajectory effect becomes of considerable
concern, especially since only large droplets are affected, which are most
influential in determining the mass flux.
The consequences of the slit effect on the calculation of the particle diameter
from the measured phase difference are the same as those explained in
connection with the trajectory effect, because the presupposed scattering
mechanism (refraction) is suppressed. This is graphically depicted in Figure
2-21, again using ray tracing (geometric optics).
Projeced slit
Intersection volume
BSA Flow Software:Reference guide 7-31
Y
Z
Z