Jasco RI-2031 Instruction Manual
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Contents
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6310.1.2 Optical systemLight sourceSlitFirst photodiodeCollimator lensFlow cell Half mirrorSecond photodiodeZero glass(motor driven)Figure 10.2 Optical SystemLight from the light source passes through a slit and into the collimator lenswhere it is made into a parallel beam. The parallel light then passes throughand 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 remainderof 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 indexchanges, thereby changing the angle of deflection in accordance with equation(1). The light image striking the primary photodiode will therefore shift in thehorizontal plane (direction perpendicular to the plane of this paper).The amount of shift is proportional to the angle of deflection and the focallength of the lens. When s is the amount of shift and f is the focal length of thelens, 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 thelight 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 surfacesand are referred to as PD1 and PD2, respectively. |
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