Sper Scientific 300038 Software for 300037 Refractometer - Manual (Page 8)

8
CUSTOMS SCALES
Your Programmable Refractometer comes preloaded with the commonly used Brix and nD (refractive index) scales. In
addition you may purchase many application-specific scales from your Sper Scientific Ltd. dealer or create your own
custom scales. An unlimited number of scales can be stored in the software’s database. Transfer these from your
computer to the three numbered display positions on Programmable Refractometer using the using the built-in RS232
computer interface. Once a scale is loaded onto your refractometer you will be able to conduct measurements in it,
independent of a computer. Scales can be loaded and unloaded from your database to your refractometer at any time.
Figure 5
Create Your Key-Values
Before creating your custom scale, you need to gather refractive index data for key-values. Generally, all custom scales start
with a refractive index value of 1.3330 nD (refractive index) for the zero point. The nD at other points varies depending on
the solution you wish to measure. Many refractive index charts are available for known concentrations of pure substances
dissolved in water. Refer to the relative literature for the arithmetic used to convert these nD values to values for your
solution.
If you are unable to locate a chart for the solution you wish to measure you can create one by preparing solutions
of known concentrations to acquire the nD of the zero point, mid-range, and maximum point. These three points are
essential when generating a custom scale. Although only three key-values are necessary, you may use up to 21 key-
values to define your custom scale. The more key-values entered, the greater the precision of your Custom Scale. We
recommended entering values that are proportionally divided. Figure 6 illustrates sample key-values for a scale of 0-26%
sodium chloride by weight.
Refractive Index Value (nD) of NaCl (% by weight)
0% = 1.3330
5 % = 1.3418
10% = 1.3505
15% = 1.3594
20% = 1.3684
26% = 1.3795
Figure 6