Application of chromaticity coordinates for solution turbidity measurement

In this paper, we describe a new turbidity sensing method based on the measurement of chromaticity coordinates. The new method measures turbidity using the transmission method, but omits the original light-intensity reference channel. The absorbance of a given solution, which is indicative of the absorption and scattering of the incident light by the undissolved matter, indicates the solution turbidity. Because the gradients of the absorbance curves increase at shorter wavelengths and differ for different turbidity solutions, the chromaticity coordinates of the solution shift with varying turbidity. The experimental results indicate that a good linear relationship exists between the chromaticity coordinates and the turbidity for a wide range of turbidity values. The slopes of the linear fits are 0.00037, 0.00034, and −0.00071/NTU for the x, y, and z chromaticity coordinates, respectively. Further, the turbidity is almost not affected by a change in the light intensity or the dark spectrum, which allows the omission of the original light-intensity reference channel. Therefore, it is not necessary to take into account the shift of light intensity and detector response in long-term measurement. The proposed method is suitable for colored water samples, provided the appropriate chromaticity coordinates are selected. In addition, the turbidity of real water samples is measured using the proposed method, and the results indicate the technique applicability.