User manual

4
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 HI 96801, 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 HI 96801
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.