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C H A P T E R 4
'
Making a measurement
P a g e 4 . 6
G e t t i n g S t a r t e d
The lens cut off point is only an issue when using the Mastersizer for spray
measurements. Other forms of measurement use a cell to confine the samples
within the measurement zone.
N o t e
.
It should be noted that spray measurements can be made with the
sample beyond the cut-off point but the outer detector elements must
be removed from the analysis using Kill data.
Always measure a background
The background measurement is used to subtract the ambient light signals from
the total scattering received from your sample. This allows the instrument to
differentiate stray light from sample scattered light and is important for accurate
results. The background should ideally be freshly taken for every sample that you
analyse. It is advisable to measure the background as near as possible to the time at
which your sample is to be measured, to avoid changes in ambient lighting
conditions.
Exceptions to this rule occur when you wish to run a series of measurements on
the same sample. Here the one background measurement is applied to all the
measurements. This is necessary to allow them to proceed without operator
intervention. In such circumstances the user is advised to operate under stable
lighting conditions if the sample area cover is removed from the instrument (i.e.
when measuring sprays).
We shall now go through the practical steps in making a measurement.
Instrument preparation
By now you should have connected the system by following the instructions in
the installation manual and the dispersion unit manual (We are assuming that you
are using Automated Sample Dispersion unit - if not consult the manual of the
accessory that you do have). Check that:
. The computer, optical unit and dispersion unit are connected and switched
on.
. For this measurement the 300RF lens (Mastersizer S) or the 45mm lens
(Mastersizer X) is fitted and both lens caps are removed.
. The beam expander is fitted and the lens cap removed.
M A N
0 1 0 1
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