The COD351 series of online digital sensors developed and produced by Daruifuno adopt the principle of UV absorption method and are suitable for online continuous monitoring of water quality chemical oxygen demand values. So why does COD monitoring use 254nm ultraviolet light source? First of all, organic substances containing aromatic rings and unsaturated bonds have characteristic absorption of ultraviolet light of specific wavelengths. The ultraviolet absorption method uses this characteristic of organic matter to determine the concentration of organic matter in water by measuring the ultraviolet absorbance of the sample. Secondly, the measurement light source of the UV absorption COD Sensor is usually 254nm UV light because the absorption values of many organic substances are relatively stable at this wavelength. Suspended solids and colloidal substances in the sample will also absorb a certain amount of ultraviolet light, affecting the accuracy of the measurement results. Therefore, in order to compensate for the influence of sample turbidity, the Cod Sensor adds a beam of ultraviolet light as a reference light source. After the ultraviolet light passes through the sample cell, the measurement light and the reference light are separated by a spectrometer, and measured by the signal detector and the reference detector respectively. After deducting the absorbance deviation caused by interference factors, the UV absorbance of the sample can be calculated.