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Low–Level Turbidity Measurements: A Comparison of Instruments
Author(s) -
Letterman Raymond D.,
Johnson Chris E.,
Viswanathan Sudhakar
Publication year - 2004
Publication title -
journal ‐ american water works association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.466
H-Index - 74
eISSN - 1551-8833
pISSN - 0003-150X
DOI - 10.1002/j.1551-8833.2004.tb10684.x
Subject(s) - calibration , turbidity , range (aeronautics) , measuring instrument , analytical chemistry (journal) , remote sensing , materials science , environmental science , chromatography , mathematics , statistics , chemistry , physics , geography , composite material , geology , thermodynamics , oceanography
The interinstrument variability of an assortment of six bench‐top and four portable turbidimeters was evaluated using four calibration materials, including user‐prepared formazin, commercial formazin, commercial stabilized formazin, and commercial suspensions of polystyrene latex microspheres. The calibration method/material, the type of light source, and the use of an instrument's ratio‐measurement feature did not have a significant effect on agreement among the instruments. However, the results divided the instruments into two groups. The instruments in group A are those that do not automatically set a predetermined reading when a sample of low‐particle (dilution) water is put in the instrument during the calibration procedure. The instruments in group B use the calibration procedure to automatically set the low‐particle reading at either zero or 0.02 ntu. Both groups include portable‐type instruments and different types of light sources. Over a turbidity range of approximately 0.01–0.5 ntu (measured by the group A instruments), the mean readings for group A instruments were about 0.1–0.3 ntu higher than those for group B.