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Many refractometers have built in "Automatic Temperature Compensation" (ATC), which is based on knowledge of the way the refractive index of sucrose changes. For example, the refractive index of a sucrose solution of strength less than 10 °Bx is such that a 1 °C change in temperature would cause the Brix reading to shift by about 0.06 °Bx.
A refractometer is a laboratory or field device for the measurement of an index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law .
Refractometers are frequently used by grape growers and kiwifruit growers for Brix testing of sucrose levels in their fruit. Refractometry is also used in the gelatin industry. To convert the RI of a gelatin sol (reported in Brix) to a gelatin concentration, one need only multiply by eight-tenths (0.8). A sol with a 10.0 RI would therefore be 8 ...
A rough conversion between specific gravity, SG, and either degrees Brix, Plato or Balling can be made by dividing the thousandths of SG above 1 (which is often referred to as gravity points) by 4. So a specific gravity of 1.048 has 48 gravity points, and 48 divided by 4 would be approximately 12 degrees Plato, Balling or Brix.
These are to be used with the analysis methods that characterize sugars by refractometric means but find wide application outside the sugar industry as the sucrose polynomial is built into the firmware of modern refractometers and is the basis for calibration of purely optical refractometers which read in Brix.
In the Abbe refractometer the liquid sample is sandwiched into a thin layer between an illuminating prism and a refracting prism. The refracting prism is made of a glass with a high refractive index (e.g., 1.75) and the refractometer is designed to be used with samples having a refractive index smaller than that of the refracting prism.
The result may be displayed in one of various units of measuremeant: Brix, freezing point, boiling point, concentration, etc. Nearly all digital refractometers feature Automatic Temperature Compensation (for Brix at least)
A traditional handheld refractometer is an analog instrument for measuring a liquid's refractive index. It works on the critical angle principle by which lenses and prisms project a shadow line onto a small glass reticle inside the instrument, which is then viewed by the user through a magnifying eyepiece.