Research Of Optical Fiber Vibration Sensing System Based On OTDR And FBG

No matter in industry or people's life,vibration is a common phenomenon.Vibration frequency information is one of the important parameters to describe vibration,and its measurement is an essential part of vibration monitoring.Traditional fiber grating(FBG)vibration sensors mainly measure the vibration frequency by scanning wavelength,which takes a long time and is difficult to measure high-frequency vibration events.In view of this shortcoming,this paper proposes an optical fiber vibration sensing scheme based on OTDR and FBG.This scheme USES the edge filtering method to measure the vibration frequency of FBG,and USES the OTDR function to measure the length of optical fiber,In the end,the length and vibration frequency of optical fiber can be measured at the same time in a set of system.At the same time,in order to reduce the cost of signal processing module,this paper also proposed the use of ARM development board as a signal processing unit,vibration frequency measurement program.This paper is mainly divided into the following aspects:1.The basic theory and classification of fiber Bragg gratings,the basic technology and classification of fiber Bragg gratings and the status quo of OTDR sensing technology are summarized,and the sensing principle and demodulation technology of fiber Bragg gratings are emphatically discussed.2.An optical fiber vibration sensing scheme based on OTDR and FBG is proposed,which can realize simultaneous measurement of optical fiber length and vibration frequency.The vibration events of 850 m terminal with vibration frequencies of 1200 Hz,1000Hz and 800 Hz were measured successfully in the experiment,and the fiber length and loss coefficient were obtained at the same time.3.In order to reduce the cost of vibration measurement structure and obtain demodulation information in real time,this study proposes a set of vibration measurement system based on edge filtering method and ARM plate.The system is divided into two structures: circuit board and ARM board.The circuit board mainly converts optical signals into electrical signals and conducts voltage amplification,and inputs the amplified voltage to ARM board.The main taskof ARM board is to collect the input electrical signals for ADC conversion,carry out Fourier transform on the converted signals,and display the frequency on the screen through peak finding processing and calculation.System test shows that the system can measure the frequency of vibration events below 2kHz due to the sampling frequency limitation of ARM plate.Since there is no need for oscilloscope and computer,the system has the advantage of low cost and can get the vibration frequency information immediately.