Jasco RI-2031, Инструкция по эксплуатации

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10.1.2 Optical system
Light source
Slit
First photodiode
Collimator lens
Flow cell
Half mirror
Second photodiode
Zero glass
(motor driven)
Figure 10.2 Optical System
Light from the light source passes through a slit and into the collimator lens
where it is made into a parallel beam. The parallel light then passes through
and is refracted by the flow cell. Part of the light is reflected by a half mirror,
passes through the cell again, and strikes the first photodiode. The remainder
of the light passes through the half mirror and strikes the second photodiode.
If the concentration of the sample in the cell changes, then the refractive index
changes, thereby changing the angle of deflection in accordance with equation
(1). The light image striking the primary photodiode will therefore shift in the
horizontal plane (direction perpendicular to the plane of this paper).
The amount of shift is proportional to the angle of deflection and the focal
length of the lens. When s is the amount of shift and f is the focal length of the
lens, the following equation can be expressed.
s = 2f x θ ... (2)
The coefficient of 2 is required in the equation to account for the fact that the
light passes through the flow cell twice and is therefore refracted twice.
The method for detecting the amount of shift is described below.
The first and second photodiodes contain identical photo-sensitive surfaces
and are referred to as PD1 and PD2, respectively.