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How does an online turbidimeter measure turbidity?

by:BOQU     2022-02-18

An online turbidity meter is often used in the turbidity monitoring of the water produced by the water plant; the water quality monitoring of the municipal pipe network; the water quality monitoring of the industrial process, circulating cooling water, activated carbon filter effluent, membrane filtration effluent, etc. Turbidity refers to the degree of obstruction of a solution to the passage of light, which includes the scattering of light by suspended matter and the absorption of light by solute molecules. The turbidity of water is not only related to the content of suspended substances in the water, but also to their size, shape and refractive index. Turbidity is generally applicable to the quality measurement of natural water, drinking water and some industrial water.

The water sample for measuring turbidity with an online turbidimeter should be quick, or it should be refrigerated at 4°C and measured within 24 hours. Before the measurement, the water sample should be shaken vigorously and returned to room temperature. The water contains soil, silt, fine organic matter, inorganic matter, plankton and other suspended solids and colloids, which can make the water turbid and cause certain turbidity. The water quality analysis stipulates that the turbidity composed of 1mg SiO2 in 1L water is one Standard turbidity unit, referred to as 1 degree. Generally, the higher the turbidity, the more turbid the solution.

The incandescent light emitted from the sensor light source assembly of the online turbidimeter enters the turbidimeter downward, and scatters light when it encounters suspended particles in the sample. The sensor's photodetector immersed in the water sample is able to detect scattered light at a 90° angle to the incident beam.

The continuously moving water sample flows through a patented air bubble removal system that removes trapped air bubbles in the sample stream, thereby eliminating significant disturbances in low turbidity measurements; The effect of changes in sample flow rate and pressure.

The turbidity sensor consists of two parts, the laser light source and the light intensity sensor. The stability of the laser light source directly affects the accuracy and reproducibility of the measuring instrument. Using halogen tungsten lamps as the light source of the turbidimeter only takes several hundred to several thousand hours, while the selection of laser components not only saves energy and protects the environment, but also increases the lifespan to 5 years. Therefore, a laser element is selected as the light source, and a constant current source is used to stabilize the light source. The light intensity sensor detects how much light is scattered by the particles in the water from the direction of 90° to the incident light. The light intensity of the scattered light received by different turbidity is different. The sensor processes this change signal into a current signal and transmits it.

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