What does nephelometer measure and in what units?

Answer 1

A nephelometer is an instrument for measuring suspended particulates in a liquid or gas colloid. It does so by employing a light beam (source beam) and a light detector set to one side (usually 90°) of the source beam. Particle density is then a function of the light reflected into the detector from the particles. To some extent, how much light reflects for a given density of particles is dependent upon properties of the particles such as their shape, color, and reflectivity. Therefore, establishing a working correlation between turbidity and suspended solids (a more useful, but typically more difficult quantification of particulates) must be established independently for each situation.

Because optical properties depend on suspended particle size, a stable synthetic material called "Formazin" with uniform particle size is often used as a standard for calibration and reproducibility. The unit is called Formazin Turbidity Units(FTU).

Nephelometric Turbidity Units (NTU) specified by United States Environmental Protection Agency is a special case of FTU, where a white light source and certain geometrical properties of the measurement apparatus are specified. (Sometimes the alternate form "nephelos turbidity units" is used.)

Answer 2

A nephelometer is used to measure the amount of light scattered by suspended particles in a liquid or gas sample. The units of measurement are usually reported in Nephelometric Turbidity Units (NTU) or Formazin Turbidity Units (FTU), depending on the standard method used.