The Research Of Scheme And System For Tiny Particles Concentration Detection

Tiny particles in the liquid scatter light as they do in the air. Based on the scattering theory a particle concentration detection scheme and setup are presented in this thesis. The lateral scattered light, which corresponds to the particle concentration, was collected and detected at a fixed angle, and then the concentration could be determined. Since most of bacteria are with several micrometers size and thus also scatter light, the possibility of such detection scheme applied in bacteria detection are also discussed, and a real-time detection of bacteria concentration was performed.The 90-degree scattering model and an infrared LED with central emitting wavelength 850 nm as light source were employed. When light irradiating the turbid liquid, the optical detector was utilized to receive the scattered light, and signal processing modules were designed to achieve signal amplification and comparison. Then the square wave signal, which the duty cycle related to the particle concentration, was obtained. In order to lower noise, e.g., caused by ambient light, the experimental liquid was placed in a dark chamber.The turbidity of standard Formazine hydrazine solution was measured with the measurement setup. The experimental results show a good linearity in the range of 30-70 NTU. In order to verify the possibility of system used for the bacterial solution measurement, continuous measurements were carried out during the cultivation process of colibacillus. The concentrations of colibacillus showed a growth over time and the detected signal had the same trend which is consistent with the curve of bacteria culture. Experimental results show that the proposed scheme and the setup can be used for the detection of bacterial culture process.