Study On Optical Fiber Fabry-Perot Cavity Liquid Level Sensor By Interference Fringe Counting And Its Temperature Compensation

Because of optical fiber's portability and immune to electromagnetism, the development and application of liquid level sensors based on optical fiber are concerned with. Especially, in the application of measurement and control of flammable liquid, optical fiber sensors are the better choice.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 series of discussions and improvements are conducted. The research work will be illustrated from the following four aspects:Firstly, in terms of judging direction change and counting of interference fringes, an electric circuit method by usingπ/2 electric RC phase shifter is proposed. This technique can omit some expensive optical devices, simplify the sensor system, and reduce the difficulty and complexity of the system adjusting effectively. A pre-amplify circuit was designed so as to capture the signal.Secondly, in data acquisition, the computer software was re-designed and optimized.Thirdly, in temperature compensation, a design for compensating temperature influence on the sensing result by software approach is suggested. This method use temperature sensor to real-time feedback cavity temperature change, then employ the empirical formula measured and obtained from the sensor system beforehand to calibrate the sensor. The experimental results show that this software technique can effectively compensate the temperature drift impact.Fourthly, in order to eliminate the difficulties encountered in the experiment and practical application, the structure improvement of sensing head was suggested. A layout to ease the adjustments of the GRIN (gradient-index) lens is proposed.