The Basics of Process Refractometers

Light refractionA refractometer is a process instrument capable of determining a solution's refractive index. Light bends and changes velocity as it travels from one media into another through the media interface. When light traveling through air enters liquid, the light rays change direction by an amount determined by the liquid's density.

Angle of refraction refers to the magnitude the light bends as it exits one media and enters the interface of another. With the angle of refraction defined by their densities, different liquids display different amounts of refraction - for example, a higher density juice such as orange juice will have significantly different refraction than cranberry juice, because of its higher density.

Light refraction
Light bends when traveling through
different media. That's why this pencil
appears to be "broken" when it enters
the water.
A liquid's refractive index relates to the amount of light bending that liquid displays. The greater the bending, the greater the refractive index. The lower the bending, the lower the refractive index.

Standard tables are available that correlate refractive index to a variety of materials. These same tables also correlate refractive index to varying concentrations of particular liquid media at a particular temperature. Take corn syrup for example. Different refractive indexes are observed for different corn syrup samples of different concentrations. Therefore, by using a process refractometer to observe the refractive index of a particular corn syrup sample, a determination of the concentration of that particular sample can be made. By referring to the table or scale that correlates the refractive index to concentration at a particular fixed temperature, liquid concentration can be determined.

The refraction index of the liquid medium readings will vary at different temperatures, and therefore, the sample's temperature must be measured and compensated for in order for refractive index readings to be accurate and repeatable.

Refractive index measurements have been used for process control in the food, juice and beverage industries for decades, with the most common applications being the measurement of sugars (Brix) and total dissolved solids (TDS). Large scale production and processing of fruit juices, jams, tomato products, wine, beer, coffee, and many other products rely on industrial refractometers for quality and consistency.

For more information contact Electron Machine Corporation by visiting or by calling 352-669-3101.