ETHANOL PRODUCER'S DATA BASE

Simplicity in Applied technology

Refractometers

In Line Process Refractometers

Working Principle:

  • The light from an LED source is transmitted by a fiber optic onto one side of a measuring prism and internally reflected to the interface of the prism and the sample liquid.
  • A portion of this light beam is reflected back onto the opposite side of the prism at an angle which depends on the refractive index of the liquid at the interface.
  • The position of this reflected beam, as it exits the prism, changes with the angle of reflection (which depends on the refractive index of the sample ).
  • A linear diode array is used to accurately detect the varying position of the reflected beam and this position is calibrated with respect to refractive index.
  • As there are no moving parts, only precise optical and electronic elements, the calibration is very stable, repeatable and accurate.

 

SOURCE: http://www.topac.com/to02006.html

Refractometer Scales

Brix scale

  • Refractometers are widely used to measure the amount of dissolved substances in solutions containing mainly sucrose.
  • The relationship between refractive index and the amount of dry substance content is well known for sucrose and is the basis of the Brix scale which is measure of the number of grams of sucrose present per 100 grams of aqueous sugar solution.   
    • 50 Brix means 50 grams of solid per 100 gms of solution
  • This relationship holds for a large number of similar substances and so the Brix scale is widely used in the food industry.
  • Unfortunately the refractive index of a sugar solution changes with temperature while its solid content remains the same. 
    •  The same refractive index at different temperatures correspond to different Brix values.
  • Manual "Abbe" refractometers do not compensate for this temperature effect and manual correction tables should be used to adjust the readings to a standard temperature.