DHR/AR Series SALS Accessory Getting Started Guide
Page 24
To use the Laven program:
1
Select from the following parameters:
2
For the remaining two text boxes, select
Mie
and
Intensity v. scattering angle
.
3
Click
New plot
to perform the calculation. The results can be exported as a text file from the
File
menu,
which can then be opened directly by Microsoft Excel.
The first column in the results text file is headed Angle theta (these values are in degrees). The data in this
column can be converted to
q
values using the formula q = 4
π
n
/
λ
0
sin(
θ
/ 2), where
n
is the medium
refractive index ( ~ 1.332 for water), and
λ
0
is the wavelength of the laser light in a vacuum. Since the
units of
q
are usually µm
-1
, the laser wavelength should also be in µm, i.e. 0.6328 (NB Excel uses radians
for angles). This line works:
=(SIN(A20*2*PI()/360))*4*PI()*1.332/0.6328
Parameter
Instructions for SALS
Intensity Scale
Select
Logarithmic
.
Leave
Maximum
and
Minimum
as
Automatic
.
Light Source
Select
Point
.
Angle Scale
Minimum angle
and
Maximum angle
. These refer to the scattering angle in degrees; typically
0 and 30 respectively seem appropriate.
Angular resolution
. This is the resolution to which the Mie curve will be calculated. If it is set
too high, the curve will not be smooth. If it is set too low, the calculation will be excessively
time-consuming. A value of 0.1 gives a reasonable compromise.
Drop Size
Diameter (µm)
. Enter the value for
Calibrated Particle Diameter
from the Certificate of
Analysis, but note that the default for the Mie program is radius. Diameter can be selected from
the
Advanced
menu.
Select
Disperse
and scroll to either
Normal
or
Log-normal
(it doesn't seem to matter which is
selected).
Std Dev %
(i.e., standard deviation %). Enter the value given on the Certificate as
CV
(i.e.,
coefficient of variance), which is the same thing.
N
is the number of slices in the particle size distribution. The higher this is set, the longer the
calculation takes, but it is fast enough when left on 50.
Light
Number of wavelengths
leave as 1, as laser light is monochromatic.
Wavelength (µm) in vacuo
. Enter the wavelength of the laser light, which is
0.635 µm.
Refractive index (sphere)
. For
Real
use the value given on the Certificate for Refractive index
(strictly speaking, this was not measured at the correct wavelength or possibly temperature, but
the difference will be negligible). For
Imaginary
use zero.
Refractive index (medium)
. Use the refractive index of water, which is about 1.332 (as with
the spheres, this varies with wavelength and temperature, but the effect is negligible).
Polarization
. Select as appropriate. Either
perpendicular
or
parallel
options can be used with
TA Instruments SALS system.
