The LISST-200X has been designed to cover a wide range of concentrations of
particles. However, when the concentrations are high the light scattering from the
particles can included multiple scattering which will affect the measurement of particle
size and concentration. The concentration where multiple scattering can take effect is
dependent on particle size. The finer the particles are the lower the maximum
concentration where multiple scattering will occur. The rule-of-thumb we recommend is
when the optical transmission is less than 30% multiple scattering may be significant
enough to cause errors. The multiple scattering gradually increases as the
concentration increases. Therefore, 30% optical transmission is a warning level where
multiple scattering may be present. It may still be possible to get reasonable data down
to 10% transmission. Below is a table with estimates of the maximum concentration for
different sized particles.
To measure higher concentration with the LISST-200X the optical path that the laser
passes through needs to be reduced. By reducing the optical path, we decrease the
number particles in the laser beam and therefore reduce the chances of having multiple
scattering. The maximum concentration scales linearly with the optical path. If we
reduce the optical path by ½ we double the maximum concentration. Sequoia has
designed a Path Reduction Module (or PRM) for the LISST-200X that reduces the
optical path from 25mm to 5mm. This results in increasing the maximum concentration
by a factor of 5 over the standard LISST-200X.
Table 1: Estimated maximum concentration for different sizes and different path lengths
The following sections include detailed instructions for installing, uninstalling and
maintaining the Path Reduction Module for the LISST-200X.
