MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont)
Turbidity: Turbidity is defined as an expression of the optical properties of a sample that cause light rays to be scattered and absorbed, rather than transmitted in straight lines through a sample. ASTM further describe turbidity as the presence of suspended and dissolved matter, such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. Implicit in this definition is the fact that colour, either of dissolved materials or of particles suspended in the water also can affect turbidity.
Turbidity sensors operate differently from those for temperature, specific conductance, DO, and pH, which convert electrical potentials into the measurement of constituent of interest. Submersible turbidity sensors typically direct a light beam from light-emitting diode into water sample and measure the light that scatters or is absorbed by suspended particles in water.
Most commercially available sensors report data in Nephelometric Turbidity Units (NTU)/ with a sensor range of 0-1000 and an accuracy of -+5 percent or 2NTU, whichever is greater.