Don't Spray The Optical Unit; Ensure The Spray Is Stable During Measurement - Malvern Mastersizer Series Getting Started

A P P E N D I X E

Don't spray the optical unit

Ensure the spray is stable during
measurement
P a g e E . 2
G e t t i n g S t a r t e d
ligaments that will later divide into stable droplets. Thus the limiting minimum
distance may not be set by concentration considerations alone.
In other sprays the droplets themselves may be volatile and evaporate rapidly
causing size distributions that will change with distance from the nozzle.
For all of the above reasons it is important to choose carefully the distance
between the nozzle and the analyser beam. Having set a suitable distance satisfied
by measurements, continue to use this configuration every time.
It is most common for measurements to be made with the analyser beam
intersecting the centre of the expanding spray cone. The result reported is the
average size distribution in the volume of spray in the beam. By moving the beam
off the spray axis it is possible to obtain the average size distribution in a different
part of the spray. By this means it is possible to probe the spatial variation of size
distribution and hence obtain further diagnostic information about the nozzle
characteristics.
Care is required to avoid the spray settling on the lenses. The droplets formed
will scatter light and distort the size distribution accordingly.
Variations or inconsistent spray performance during the measurement can lead to
fluctuating results. Try to ensure that the spray conditions are stable and if
fluctuations are inherent remember to increase the measurement interval so that
averaging increases the result stability. If you wish to probe time variations in the
size distributions then you must use the Spray Synchroniser accessory which
allow accurate time resolution of the size measurement. For advice on making
pulsed spray measurements please see 'Spray Measurements' in the Software
Reference manual.
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