The optical level sensor FS-IR1902 refracts the infrared light emitted by the internal transmitting tube, and judges whether the sensor is in a water state according to the amount of photoelectric light received by the internal receiver. If only a small amount of light is received or is not received because the light is refracted in the water, it is judged to have a water state. Photoelectric type is affected by the working principle because it is infrared light, but has nothing to do with factors such as pressure, temperature, density, corrosivity, etc., and has little effect on the measured medium. Because of high repeatability and high detection accuracy, it has the characteristics of high reliability and long lifetime.