Research On Soft-demodulation Technology Of High Precision Water Level Measurement System Based On Optical Fiber Interferometer

Tsunami disaster is highly destructive. It is urgent to have a research on tsunami warning technology. The water level measurement technology is an important means of tsunami warning. Changing the traditional water level measurement technology, to make the real-time monitoring results more accurate and to achieve the purpose of disaster prevention and mitigation. Optical fiber sensing technology for water testing has become a trend, and as a new technology of water level measurement, it possesses the advantage of immunity to electromagnetic interference, resistance to chemical corrosion, high precision and so on. It can be applied in complex marine environment, so it has high scientific value and usefulness.Firstly, the principle and design of the water level sensor based on optics fiber interference are analyzed deeply in the dissertation. Starting with the theory, the principle of optical interference and the phase modulation mechanism during fiber stress strain are caused;the relation between water level and the phase change is established;the coupling characteristics of the 3 * 3 coupler is analyzed, and the phase differences between the output waves from 3*3 coupler is 2?3. According to the feature, we build the water level measurement system based on optics fiber Mach-Zehnder interference that can distinguish direction.Secondly, the signal demodulation module is the key component for this system. In this paper, the underlying hardware preparation is completed first. In order to realize the signal demodulation we presents the interference fringe counting method with dynamic double threshold, which can improve the resolution of the system and reduced the demand of the dynamic range of the strain component; the computer and hardware module is combined with the virtual instrument to realize the demodulation of the phase signal and the real-time display of the water level information. Compared with the traditional counting method based on circuit, the lower cost and the shorter production cycle are achieved by the software demodulation method; this method can also avoid the electrical noise of the hardware circuit and make the signal processing flexible.Finally, the experimental verification for the soft-demodulation scheme of the optical fiber water level measurement system is carried out. The experimental results shows that the linear correlation coefficient is 0.99991; after calculation and simulation, the maximum resolution of the system that is obtained is 1.59 mm and the measurement accuracy of water level is 0.01% of the full range. The desired accuracy index is achieved. As a result, the measurement method of high accuracy water level detection based on the optical fiber interference is feasible, it’s extremely worthy to study it in-depth for its extensive application.