Capturing the scattering pattern
This section describes the principles of the Spraytec’s operation.
Fundamentals
The fundamentals of Spraytec spray measurement are shown in this diagram:
The process is:
.
Light from the laser
+
is scattered by the spray droplets
-
.
.
The laser beam is expanded by the collimating optics
,
to provide a wide
parallel beam.
.
The scattered light is focussed by a focussing lens
.
in a Fourier arrange
-
ment and picked up by the detector array
/
.
.
Unscattered light is focussed by the focussing lens
.
, so that it passes
through the pinhole at the centre of the detector array. This is measured by
the beam power detector (detector 0) to give the light transmission.
.
The angle at which a particle diffracts light is inversely proportional to its
size. The detector array is made up of over 30 individual detectors, each of
which collects the light scattered by a particular range of angles. There is a
data channel for each of these. Measuring the angle of diffraction deter
-
mines the size of the particle, as shown in the following diagram.
CHAPTER 2
Spraytec Page 2.3
1
2
3
4
5
ILL 7424
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