Application Study On Optical Fiber Liquid Level Sensor By Using Interference Fringe Counting Technique

Optical fiber liquid level sensor is a new type of liquid level sensors, it possesses the advantages of high accuracy, intrinsic safety, resistance to chemical corrosion and immunity to electromagnetic interference. Optical fiber liquid level sensor is in keen demand in petroleum and chemical industry, and in huge oil depots.In order to put optical fiber Fabry-Perot cavity liquid level sensor with fringe counting technique to be more practical and easier for application promotion, a study was conducted thoroughly and seriously in the sensor hardware and software improvements.A design for fringe direction change distinguishing with a configuration of double optical fiber channels is proposed. The working principle, structural design and actualization of the layout were investigated in detail. It shows that this method is easy to be carried out, and the difficulties of manufacture and regulating can be reduced.Double-extrema adopting in the fringe counting is proposed, then the demand of the dynamic range of the strain component could be reduced much more, and the resolution of the sensor system might be enhanced significantly. Dynamic threshold setting is used for reducing the requirement of the system stability and keeping the long-term reliable running of sensing.A virtual instrument system based on the LabVIEW is suggested. The virtual system can treat with the photoelectrical signals effectively, and display the liquid level on a screen directly. The practical programs for the liquid overflow alarm and the liquid level change record are configured for the oil storage operation.An optical fiber liquid level sensing system by using interference fringe counting technique was assembled. The experimental results show that the linear correlation coefficient is 0.9999, the maximum resolution is 0.8846mm in the measuring range of 10m water height.All of the above-mentioned improvements can reduce the manufacture difficulties, enhance the practicability and operability, and increase the resolution of the sensing system.