The RDO Pro fluorescence method determines the concentration of dissolved oxygen in water by measuring the time it takes for fluorescent substances on the probe surface to emit red light. The sensor cover at the forefront of the measuring probe is covered with a layer of fluorescent material. The blue light emitted by the light source shines on the fluorescent material, and the LED fluorescent material is excited and emits red light; A photovoltaic cell detects the time required for a fluorescent substance to return to its ground state from emitting red light. This time is only related to the emission time of blue light and the amount of oxygen. The probe also has an LED light source, and the more oxygen around the sensor, the shorter the time for the fluorescent substance to emit red light.