Ametek 1400700, Руководство пользователя

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1400700-101 Rev. A
What is refractometry?
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Examples
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Therefore one can neither say straight lines nor parabola are adequate for a device that should
reach a precision of 0.01 Bx !
With a third-order function the maximum error at the seven support points would be only 0.01 Bx .
But be careful ! The result of a measuring of a 65 - Bx -sample would be 65.04 Bx with a third or-
der function. It is a general problem of all polynomal fits that they are unsteady beyond the support
points. If you only have values from 0 to 60 Bx , it means, that the scale is only secured up to 60 Bx .
Let us take a look to the temperature correction. If you are using a manual Abbe-refractometer
with a defined brix scale, you also got a table with temperature corrections that came with it. Ac -
cording to this table the measured value is changed per degree Centigrade about 0.06 Bx at water
and about 0.08 Bx at 60 Bx . Since the parabola does provide good results, a linear correction of
0.07 Bx / °C is adequate. But please consider that this linear correction of 0.07 Bx / °C is not good
enough for a refractometer that should guarantee a precision of 0.04 Bx !
Therewith
c
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would be 0.07 and all the other coefficients zero in this simplified case.
This example shows that the calculation of a special scale is not that simple. Many users probably
have a calculator that is able to determine a best-fit curve. But in the example shown above you
saw that this was not sufficient, because you can achieve an accuracy range of 2 Bx .
Starting point of all calculations is respectively a table with values that the refractometer should
show (set values) and the corresponding refractive indexes (or also brix values). Such a table can
also be computed with a formula you find in technical literature. For a number of particular cases we
provide you already calculated coefficients.
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Refractometry
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