Multi-Wavelength Calibration of a Low-Cost High-Range Turbidimeter: Analysis of the Dispersion Regime

Turbidimetry, a method for assessing fluid clarity by quantifying suspended particle levels, plays an important role in various fields, including environmental surveillance, sediment measurements, water quality management, and diverse industrial sectors. Various optical instruments are commercially available, normally called turbidimeter. However, no generic calibration that can be used to convert the turbidimeter output to NTU is possible. This work presents the development of a low-cost multiwavelength turbidimeter designed for high-range turbidity measurements (0.5-4000 NTU) in visible and near-infrared spectra (500-1000 nm). Using formazin solution as a turbidimetric standard and introducing the <i>calibration factor</i> concept, we were able to determine the identification of multiple calibration zones of the developed sensor. For calibration experiments, a portable spectrometer was used to measure the transmitted light, thereby obtaining a spectrum associated with each standard. Then, analysis of the obtained spectra was performed, enabling characterization of the calibration method employed in the study. Considering various wavelengths in the analysis, the results suggest that the present methodology has the potential to develop environmental monitoring practices and water quality control. More specifically, turbidity measurements can be performed in a wide range of NTU and wavelength values, suggesting the feasibility of conducting analyses over an extensive turbidity spectrum.