The in-line fluorescence optical Dissolved Oxygen Sensor (MTI.WQMS.DRFN.DO) independently developed and produced by Daruifuno is designed based on the principle of quenching excitation fluorescence by specific substances in physics. When the excitation light is irradiated on the fluorescent substance on the surface of the fluorescent membrane head, the fluorescent substance is excited, fluorescence is emitted, and the extinguishing time of fluorescence is affected by the concentration of oxygen molecules on the surface of the fluorescent membrane head. The concentration of oxygen molecules can be calculated by detecting the phase difference between fluorescence and excitation light and comparing it with the internal calibration curve, and the final value can be output by temperature and salinity compensation. This dissolved oxygen sensor can be used with the Dissolved Oxygen Controller and they are widely used in sewage treatment plants, waterworks, industrial production processes, aquaculture and other industries to monitor the dissolved oxygen value in real time.