Design of a High Resolution and Dual-Path Optical Water Turbidimeter

Abstract

We have designed a high resolution and dule-path optical turbidimeter. The right angle scatted light turbidimeter is mainly for water in low turbidity levels, especially for drinking water. Mechanical design of the optoelectronic receiving room and the realizing circuit for modulation and demodulation are described in detail. To achieve good linearity in the measuring range from 0 to 5 NTU, pulse width modulation (PWM) and demodulation techniques are proposed, in this way, low temperature-drift and good anti-jamming ability can be obtained without the interference of background light. To improve the precision, the ratio algorithm which measures the ratio of the scattered light and reflected light is introduced in a dule-path optical system so that the interference of light emission can be eliminated effectively. Through the analysis and comparison of the experimental results, the linearity is improved by the ratio algorithm with a correlation coefficient for about 0.99932.