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7
PRINCIPLE OF OPERATION
The Brix determination is 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 MA871, 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. The MA871 automatically applies temperature compensation to the
measurement and converts the refractive index of the sample to sucrose concentration in
units of percent (by weight) Brix.
