23 Inline and Online Process Analytical Technology with an Outlook …
571
The pneumatically operated sensor lock gate allows calibrating or adjusting the
measuring system as well as cleaning the sensor in the running process. The sensor
can be moved into “PROCESS” position where the probe is located in the process
medium. In “SERVICE” position, the probe is located in the calibration chamber. In
this position, the measuring system can be calibrated or can be cleaned and dried,
e.g., using compressed air. The used liquids (for cleaning or calibration) leave the
calibration chamber through an outlet hose; i.e., they are displaced from the calibration chamber by following liquids or by air. The spectrometer software detects
optical window contamination via the measuring signal, and the probe is cleaned as
required or automatically at specific intervals.
23.5 Inline Spectroscopy of Surfaces, Thin Films,
and Particulate Systems
23.5.1 Separation of Specular and Diffuse Reflectance
in PAT Applications Using Polarization Spectroscopy
23.5.1.1 Specular and Diffuse Reflectance
Light scattering is an elastic interaction between the photon and the particle. The
phenomena of reflection and scattering are thus closely related to particle size, angle
of incident of the illuminating light source, angle of detection of the observer, respectively, sensor and the difference between the refractive index of the substance and
that of the embedding medium, respectively, environment. When polarized light is
used for the measurement, specular reflected light preserves its polarization, whereas
diffuse reflected light is depolarized after scatter in all directions. Scatter also changes
the angular distribution of the scattered light. This means, the light no longer has a
preferential direction, but spreads itself in all directions. Specular reflection is always
mirrored at exactly the same angle of the incident light with respect to the surface,
whereas (ideal) diffuse reflected light is scattered in all directions.
For the measurement of diffuse reflection or transmission, ideally an integrating
sphere is used. The sample is illuminated with directed light through an opening
in the sphere. Specular reflection, where the angle of illumination and the angle of
reflection is the same, is lost in a light trap (usually, an angle of around 5° is used)
or measured directly with an additional detector. The diffuse reflected light is spread
over the whole volume of the sphere and can be measured at one spot with a detector
located where specular reflected light is avoided [47–50].
571
The pneumatically operated sensor lock gate allows calibrating or adjusting the
measuring system as well as cleaning the sensor in the running process. The sensor
can be moved into “PROCESS” position where the probe is located in the process
medium. In “SERVICE” position, the probe is located in the calibration chamber. In
this position, the measuring system can be calibrated or can be cleaned and dried,
e.g., using compressed air. The used liquids (for cleaning or calibration) leave the
calibration chamber through an outlet hose; i.e., they are displaced from the calibration chamber by following liquids or by air. The spectrometer software detects
optical window contamination via the measuring signal, and the probe is cleaned as
required or automatically at specific intervals.
23.5 Inline Spectroscopy of Surfaces, Thin Films,
and Particulate Systems
23.5.1 Separation of Specular and Diffuse Reflectance
in PAT Applications Using Polarization Spectroscopy
23.5.1.1 Specular and Diffuse Reflectance
Light scattering is an elastic interaction between the photon and the particle. The
phenomena of reflection and scattering are thus closely related to particle size, angle
of incident of the illuminating light source, angle of detection of the observer, respectively, sensor and the difference between the refractive index of the substance and
that of the embedding medium, respectively, environment. When polarized light is
used for the measurement, specular reflected light preserves its polarization, whereas
diffuse reflected light is depolarized after scatter in all directions. Scatter also changes
the angular distribution of the scattered light. This means, the light no longer has a
preferential direction, but spreads itself in all directions. Specular reflection is always
mirrored at exactly the same angle of the incident light with respect to the surface,
whereas (ideal) diffuse reflected light is scattered in all directions.
For the measurement of diffuse reflection or transmission, ideally an integrating
sphere is used. The sample is illuminated with directed light through an opening
in the sphere. Specular reflection, where the angle of illumination and the angle of
reflection is the same, is lost in a light trap (usually, an angle of around 5° is used)
or measured directly with an additional detector. The diffuse reflected light is spread
over the whole volume of the sphere and can be measured at one spot with a detector
located where specular reflected light is avoided [47–50].