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7
PRINCIPLE OF OPERATION
%Brix, °Baumé, °Oechsle, °KMW and % potential alcohol determinations are made by
measuring the refractive index of a solution. Refractive Index is an optical characteristic
of a substance and the number of dissolved particles in it. Refractive Index is defined as
the ratio of the speed of light in empty space to the speed of light in the substance. A result
of this property is that light will “bend”, or change direction, when it travels through a
substance of different refractive index. This is called refraction.
When passing from a material with a higher to lower refractive index, there is a critical
angle at which an incoming beam of light can no longer refract, but will instead be
reflected off the interface. The critical angle can be used to easily calculate the refractive
index according to the equation:
sin (
T
critical
) = n
2
/ n
1
Where n
2
is the refractive index of the lower-density medium; n
1
is the refractive index of
the higher-density medium.
In the
MA882
,
MA883
,
MA884
and
MA885
refractometers, light from an LED passes
through a prism in contact with the sample. An image sensor determines the critical angle
at which the light is no longer refracted through the sample.
