Turbidity sensor is an instrument which uses optical principle to measure the degree of turbidity of water. Turbidity is caused by suspended particles in water. The suspended particles reflect the incident light. Usually, the scattered light in the direction of 90°is used as the test signal, so the unit tested is called NTU. This method is suitable for testing low to medium range, ranging from 0.01 to 4000FNU. According to EN27027 and ISO7027 standards, infrared light of 860 nm is used as light source, which can not be disturbed by the chromaticity of samples.