HF scientific MicroTPI Field Portable Turbidimeter (Old) - Manual (Page 19)

Glossary
Formazin Nephelometric Units (FNU): see Nephelometric Turbidity Units
Formazin Turbidity Units (FTU): see Nephelometric Turbidity Units
Indexing a Cuvette: The United States Environmental Protection Agency (US EPA)
recommends that cuvettes used for turbidimeter calibration or sample measurement be indexed.
To index a cuvette with a sample in it, slowly rotate the cuvette throughout one complete
revolution (360°). While rotating the sample cuvette, observe the display and locate the
position that the cuvette is in which provides the lowest turbidity reading. This position is the
indexed position of the cuvette. Refer to section 4.2 of this manual to learn how to index a
cuvette in this instrument.
Nephelometric Turbidity Units (NTU): Unit of measure used when relating the light scattered by
a liquid media to the light scattered by a known concentration of Formazin Polymer. This unit
of measure is recognized as a measure of the optical clarity of an aqueous sample. NTU is the
accepted unit of measurement for turbidity.
Turbidity: 1) A measure of the attenuation of a radiant flux as it passes through a liquid media.
2) Optical clarity of a liquid, 3) A phenomena caused by the presence of undissolved matter in a
liquid media.
Ref. 22666 (12/04)
Rev. 1.4
15