triOS OSCAR G2, Руководство пользователя, Страница: 13 / 62

OSCAR G2
Manual
D01-44en201810
Software V.1.1.6
(C)TriOS Mess- und Datentechnik GmbH
Bürgermeister-Brötje-Str. 25
D- 26180 Rastede/Germany
13 / 62
The integrating cavity of the OSCAR (Fig. 1) has an inner diameter of 8.0 cm or 5.0 cm
(depending on the ordered version) and is made out of a diffuse reflective plastic material
(PTFE). The reflectivity of this material is depending on the material thickness, and
between ~ 94 and 97 % for a thickness of 10 mm. The surface is water-repellent to
avoid/mitigate problems with contamination. Particulate matter is easily washed out of
the cavity. The central light source consists of a small scattering sphere made out of a
diffuse quartz-glass with an outer diameter of approx. 10 mm. The light beam from the
lamp is guided to the central diffuse emission sphere by a quartz-glass rod. Similarly the
light from the cavity to the detector is guided by a second quartz-glass rod. The rod has
only a narrow field of view and, thus, does not collect any light coming from the central
light source directly. It measures the light reflected at the cavity wall opposite to the
collector as well as the path radiance, i.e. the light scattered into the receiving cone of
the collector.
2.1.2 Theoretical considerations
According to Kirk (1997) and Leathers et al. (2000),
the “transmission”,
T
AB
, measured in a
PSICAM is the ratio of the diffuse reflected irradiance F
0
at the inner wall when the cavity is
filled with either the sample A or B (Eq. 1). Each irradiance is proportional to the number of
times a photon is reflected by the wall N
C
, before it is absorbed either by the wall or by the
sample fluid. Hence,
B
C
A
C
B
A
AB
N
N
F
F
T
 
0
0
(1)
N
C
is the fraction of photons reaching the wall directly and indirectly by reflection on the wall
for one, or more times (Eq. 2). It depends (1) on the probability P
0
that a photon, coming from
the central light source, reaches the wall directly, (2) on the reflectivity of the wall

, and (3)
on the probability P
s
that a photon, which is reflected, will return to the wall. In the PSICAM
set-up used here the detector does not collect light that comes directly from the light source,
thus, for N
C
this gives
S
S n
S
n
S S C
P
P P
P P P P P P N


  

    



1
) ( ...
0
1
0
2 2
0 0
(2)