Fiber Water-level Sensor Based On Improved FBG Demodulation Technology

Water-level,temperature,pressure,and flow are also important parameters that need to be measured in industrial production and life.This article starts with the significance of the liquid level measurement,summarizes some existing liquid level measurement methods,summarizes the research status of the liquid level gauges at home and abroad.Because of its unique small size,light weight,anti-electromagnetic interference,compatibility with other optical instruments,and being less susceptible to interference from the external environment,FBG have received more attention and favor from people.The grating level gauge will have a wide range of development prospects.This article designed a fiber grating level gauge system,including FBG level gauge and FBG demodulator.The sensing principle based on the fiber Bragg grating water-level sensor is that when the liquid level changes,it will cause a corresponding change in the wavelength of the grating,the liquid level information is converted into a wavelength change,and the change of the wavelength is demodulated.Obtained level information.In the design of the FBG water-level sensor probe,a unique dual-grating structure is adopted,that is,the temperature-added grating is added to eliminate the cross-sensitivity problem.Through a large number of theoretical derivation,the relationship between diaphragm radius,thickness and deflection was obtained,and the required diaphragm size was obtained.The unique design of the structure and clips allows the grating to be in contact with the material,providing good stability and resistance to abrasion.In the selection of the demodulation method of the fiber Bragg grating demodulator,firstly,the existing methods are analyzed and compared,and the demodulation scheme suitable for our designed liquid level sensor is selected,that is,the solution based on the tunable F-P filter.To adjust the method,in order to eliminate the non-linear problem of the F-P filter,a temperature-compensated grating,an F-P etalon,and a temperature control module are added to make the calibration branch more accurate and cooperate with the tunable ring cavity laser to improve the demodulation accuracy.First,the various components that make up the demodulation system are selected,and then the circuit is designed,and a Gaussian fitting peak seeking algorithm is used to demodulate the wavelength variation to achieve the purpose of measuring the liquid level.Finally,the entire FBG water-level system designed by us was measured and verified.The experimental results show that the demodulation instrument has a measurement accuracy of 2pm,a resolution of 1.07 pm,a 24-hour stability of 1.2pm.The resolution is 0.3cm,the stability of 36 hours is 0.3cm,the measurement range is 0~3m,and the performance indexes of both parts have reached our expectations.It is proved that the water-level measurement by this system is feasible,and it has been applied in the pipe gallery system at present,and it has strong practicability.