Refractometer Calibration Terminology


ANSI – American National Standards Institute

Accuracy of Measurement – The closeness of the agreement between the result of a measurement and the (conventional) true value of the measurand. Not to be confused with “precision”. Accuracy is a qualitative concept.

Brix – A unit of measure of Sucrose (percent of sugar in a 100g cane sugar solution)

Calibration – The set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values of a quantity realized by a reference standard.

Confirmation – A set of operations required to ensure that a refractometer is in a state of compliance with manufacturers specifications and requirements for its intended use.  Confirmation includes, inter alia, calibration, any necessary adjustment or repair and subsequent recalibration, as well as any required sealing and labeling.

Error of Measurement – The result of a measurement minus the true value of the measurand.

ISO – International Organization for Standardization, a worldwide federation of national standards bodies.

NCSL – National Conference of Standards Laboratories.

Precision – The degree of agreement between two or more results on the same property of identical test material expressed as the repeatability or reproducibility of an instrument’s readings. Precision is a quantitative concept.

Refractive Index – This number is a dimensionless quantity that is related to the ratio of the speed of light in air (or vacuum) to its speed in another medium.

Refractometer – An instrument for identifying, quantitating and/or measuring substances by means of their characteristic refractive index or dispersion.

Traditional Refractometer – A hand-held device using lenses and prisms for measuring refractive index or a physical property directly related to refractive index.

Abbe Refractometer – A high precision bench-top or laboratory instrument used to measure refractive index or a physical property directly related to refractive index.

Fiberoptic Digital Refractometer – A hand-held probe type refractometer, with a fiberoptic sensor, capable of making in-situ measurements of a substance and displaying the results on a LCD display.

Range –The span between the minimum and maximum permissible readings on a given instrument expressed in a particular unit of measure.

Repeatability – See precision.

Resolution – A quantitative expression of the ability of a refractometer to permit a meaningful distinction between immediate adjacent values of the quantity indicated.

Scale Division – The distance between two graduated marks of a particular unit of measure.

Tolerance – The extreme values of an error permitted by specifications for a given instrument.

Traceability – The ability to relate individual measurement results through an unbroken chain of calibrations to one or more of the following:

    • U.S. national standard maintained by the National Institute of Standards and Technology (NIST) and/or the US Naval Observatory
    • Fundamental or natural physical constants with values assigned or accepted by the NIST (i.e., the refractive index of distilled water at 20°C, at a wavelength of 589 nm, is equal to 1.3330 refractive index [nD])
    • National standards of other countries which are correlated with U.S. national standards
    • Ratio type calibrations
    • Comparison to consensus standards

Uncertainty of Measurement – Results of the evaluation aimed at characterizing the range within which the true value of a measurand is estimated to lie, generally with a given likelihood or statistical probability. Uncertainty of measurement comprises, in general, all the many components of a measurement “system”, including instruments and calibration standards used to characterize a specific instrument. Some of these components may be estimated on the basis of the statistical distribution of the results of a series of measurements and can be characterized by experimental standard deviations. Estimates of other components can only be based on experience or other information.

Unit of Measure – A proportional amount or quantity of a specific standard of comparison.