Hanna Instruments HI 96811 - Manual (Page 5)

5
%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 (θ
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 Hanna wine measurement 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.
Specialized algorithms then apply temperature compensation to the measurement and convert this
refractive index to the model specific measurement unit.
PRINCIPLE OF OPERATION