Measurement of Turbidity Using an 850 nm Light-emitting Diode

Evaluating and managing water quality have become increasingly important owing to industrialization and environmental degradation. Currently, Korean water laws and regulations stipulate that small particles should be at a low concentration of less than 0.5 nephelometric turbidity units (NTU) in process control; hence, control technology that utilizes infrared light-emitting diode (LED) sensors remains necessary. In this study, we used 470, 670, and 850 nm LEDs to measure the light absorbance and transmittance to evaluate turbidity. The light absorbance measured using the 850 nm LED was extremely reliable, with a determination coefficient (R2) of 0.9997. The relationship between the reflected and transmitted lights at 90 and 180° was evaluated using an 850 nm light source and an 820 nm photointegrated circuit (IC) device. In addition, the effects of scattered light were determined by setting the distance between the height of the LED and the IC. From these results, we conclude that the 850 nm LED is optimal as the light source and that the effects of the horizontal distance between the LED and the IC are negligible.