A Research On Liquid Level Measurement Technology Based Fiber Bragg Grating

In addition to all the advantages of fiber sensing technologies,fiber optic grating sensors possess the distinguishing characteristics,such as immunity to the fluctuation of the light source or the light loss during transmission,capability to realize WDM (Wavelength-Division Multiplex) sensing network or distributed measuring system etc. The liquid-level sensor based on the Fiber Bragg Grating (FBG) presents many advantages over the traditional ones: flexibility of installation,low energy consumption, etc. Therefore,the study is carried out to develop a perspective fiber optic grating liquid-level sensor.In this thesis,a new liquid-level measuring system based fiber optic grating sensor is designed and developed. In the measurement system the sensing parts, similar with measurement principle of float barrel type liquid-level, is made of FBG elements and equal-intensity cantilever beam which converts the height of the liquid-level to the central wavelength of the FBG sensor. The demodulation part uses another FBG which has the same initial central wavelength of the FBG sensor, used as matching fiber grating to demodulate the central wavelength, and realized the all-fiber sensing system. Photoelectric conversion circuit and lock-in circuit to reduce the signal noise are designed and developed in the measuring system. The circuit output voltage signal is acquired through the USB type data acquisition card and the acquired data is processed by the LabVIEW. Finally, analogous experiments for liquid-level measurement with the FGB sensor system are carried out. The experiments indicate that measurement of liquid-level with FBG sensor is feasible.