Measuring Principle And Experimental Study On Parallel Coupling Spiral Optical Fiber Liquid Level Sensor

It has been a hot issue to measure liquid level exploiting optical fibers in recent years. The research of high-precision, high-reliability optical fiber liquid level sensors is of great significance in oil level measurements in industrial storage tanks and aviation fuel tanks. Many optical fiber methods have been proposed, such as float shading, magnetic, reflective and leakage. Leakage measurement method consists of reducing the thickness of the cladding method, clad-removable method, fluorescence and scattering method. Compared with other measuring methods, scattering method is more suitable, owing to its simple structure, convenience, high linearity and intrinsic safety features.This paper focuses on parallel-coupling spiral optical fiber liquid level sensor. Firstly the light transmission characteristics of the side-emitting optical fiber and the principle of the Parallel-coupling structure and spiral structure has been researched, and then a Parallel-coupling spiral optical fiber liquid level measuring method has been proposed, which ensures the linearity of the output and increases the precision as well. The lock-in amplify technology has been applied in weak signal processing circuit, which can extract weak changes in the strong background signal, and its stability is very good. It will display the voltage curve on the PC in real time using the RS232 interface for communication.After establishing a liquid level measurement environment, we develop a series of experiments, which demonstrate that the method is feasible. The result shows that it is approximately linearity, but the droplet adhesion still exists, and it is sensitive to temperature. We analyze the experimental data, explore the cause of the problem, and propose the corresponding improvement solution, which has laid a good foundation for engineering application of parallel-coupling spiral optical fiber liquid level measuring method.