Online turbidity measurement using light surface scattering

ABSTRACT On-line turbidity detecting is widely used in water purifying control and waste water processing. In this paper.scattering turbidity measurement is analyzed in terms of Mie scattering theory. An on-line turbidity measurement systemusing surface scattering technique was established. The receiving optics was elaborately designed to reduce the influence ofsample's watermark change. The turbidity accuracy ofsmaller than was obtained over the range from 0 to 1000 NTU.Keywords: Light Surface Scattering, On-line detecting, Turbidity Measurement 1. INTRODUCTION As we all know that turbidity is an important element in assessing water quality. On-line turbidity measuring is widelyused in industrial process controlling such as water purifying, waste water processing and so on. Turbidity is proportional tothe total amount oflight scattering by the presence ofparticles in the fluid1. So turbidity measuring can be divided into twogroups, a transniissiometer and a scattering turbidimeter.A transmissiometer is a transmiuance/absorptance type of turbidimeter, it measures turbidity as a decrease in intensitycaused by loss oflight from scattering and absorption by particles when a light beam is passing through the fluid sample. Soit is very sensitive to the color of fluid sample. In addition, the transmitted light intensity decreases exponentially as thefluid's turbidity increases. This makes it difficulty to measure turbidity with high accuracy, especially in high turbidityfluids. A scattering turbidimeter provides a direct measurement of light scaflered by particles in a certain viewing angle tothe incident light, and the intensity of scattered light is proportion to the turbidity of fluid sample. Therefore it can gethigher accuracy of turbidity measurement with larger dynamic range.