Optical fiber liquid level sensor for cryogenic environment

Cryogenic temperature liquids such as liquid hydrogen, liquid helium, and liquid nitrogen are widely used in aerospace, medical, and industrial production. To ensure the safety of cryogenic liquids during their transportation, storage, and use, measuring liquid level information is of great significance. Propose a liquid nitrogen level sensor based on fiber Bragg grating (FBG), which uses a stainless steel circular elastic membrane as the liquid level sensing element, is enclosed by a stainless steel circular shell, and has a dual grating structure inside. Using a finite element method, the sensitivity of the sensor elastic membrane to concentrated stress and uniformly distributed load was numerically analyzed. The influence of membrane thickness and small hole diameter size on deflection under uniformly distributed load showed that the thickness of the elastic membrane was 0.03 mm and the diameter was 84 mm; When the pressure is greater than 0.01 MPa, the sensitivity of the elastic membrane to uniformly distributed loads is 15.9 mm/MPa, and the sensitivity of the elastic membrane under concentrated stress is 0.0134 mm/N. Through liquid nitrogen level sensing experiments, it has been shown that the liquid nitrogen level height sensitivity is 0.050 nm/m, and the resolution is 1 cm. This sensor provides a reference for measuring liquid hydrogen and liquid helium levels.