HF scientific MicroTPW Field Portable Turbidimeters - Manual (Page 22)

MicroTPI & MicroTPW (5/10)
Rev. 1.9
16
9.0 Glossary
Formazin Nephelometric Units (FNU): Equivalent in value to Nephelometric Turbidity
Units (NTU)
Formazin Turbidity Units (FTU): Equivalent in value to Nephelometric Turbidity Units
(NTU)
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.
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.