AWWA JAW60510

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. Includes 22 references, tables, figures.