ATAGO Twilight AT-CM800a, Инструкция по эксплуатации

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2. Refractive Index and Brix(%)
The In-line Brix-Monitor CM-800α is a refractometer that detects the Refractive Index of a sample and outputs
the Brix(%) value on the display.
The CM-800α can also transmit measured data to external devices via 4 to 20mA or RS-232C.
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What is refractometer?
When a straw is placed into a glass filled with water, the straw appears to bend. When a straw is placed into a
glass filled with sugar water, the straw appears to bend much more sharply than in the case of water alone.
This phenomenon is known as the refraction of light. The refractometer is an instrument that measures the
Refractive Index by utilizing this principle (the Refractive Index increases in proportion to the concentration of
the solution), and was developed by Dr. Ernst Abbe at the end of the 19th century.
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What is the Refractive Index?
If the Refractive Index of air under atmospheric pressure is 1, then when
light enters medium χ, the ratio of the sine of the incident angle α
measured against the phase boundary to the sine of the refracting angle
β is called the Refractive Index of the mediumχ.
The Refractive Index varies with the wavelength of light and
temperature and is represented as follows:
n
t
D
n ： Represents the Refractive Index
t ： Temperature (℃)
D ： D-line of natrium (589nm)
For example, Refractive Index of water at 20℃ under the D-line is:
= 1.33299:
(Generally expressed as nD = 1.33299.)
m The Refractive Index is based upon the supposition that the Refractive Index in a vacuum is 1 and is
called the absolute Refractive Index. Generally, however, this index is seldom used.
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Brix(%) scale
The CM-800α is programmed with the Brix(%) scale, based on the Refractive Index of water (nD = 1.33299)
as the reference (0%). The Brix(%) scale represents the weight of sucrose expressed by percentage (sucrose
weight in grams contained in 100 grams of sucrose solution).
Therefore, this scale corresponds with the sucrose concentration. However, most samples are comprised of
ingredients other than sugar. The total concentration of these ingredients is represented by the Brix(%), so
this makes the Brix(%) scale a practical tool for measuring concentrations.
m The Brix(%) scale is recommended by ICUMSA (International Committee of Uniform Method of Sugar
Analysis) and is expressed in % mas (Sucrose) in international units (SI unit).
C The relationship between Brix(%) and the Refractive Index (nD) is outlined on page 35.
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Temperature correction
The Refractive Index of a substance varies with temperature. Thus, when using a refractometer to measure
the Refractive Index of a liquid, the measurement value will vary with the sample temperature.
The CM-800α always detects the prism temperature. The value of the measurement is automatically
corrected for temperature by a built-in processor, so that the displayed value is equal to the value measured
at 20℃ (provided that the sample temperature is within the range of 5 to 100℃).
Air
Medium χ
n=1
α
β
nχ=
sin α
sin β