source is typically infrared and the angle of particle reflection is 90
. The measurement units of these sensors are Nephelometric Turbidity Units (NTUs) or Formazin
Nephelometric Units (FNUs).
Fig. 13 Turbidity measurement methods: (a) transmissometer method, (b) backscatter method,
and (c) nephelometric method. Source: Second author
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T. Younos and C.J. Heyer