Research And Application Of Key Technology Of Displacement Sensor

As one of the key technologies of information industry,sensor technology has attracted much attention with the development of science and technology.Displacement sensor has experienced the transformation from classic displacement sensor to semiconductor displacement sensor and then to optical fiber displacement sensor.Optical fiber sensing technology has the advantages of long-distance all-weather real-time monitoring,corrosion resistance,anti electromagnetic interference,low loss,easy maintenance and so on.As an important component of optical displacement sensor,the most important link of Fiber Bragg Grating(FBG)is demodulation.Combined with the design of embedded system and the development of upper computer platform,a fast FBG demodulation system with strong reliability,high sensitivity,short development cycle and low cost is designed and built.This time,we choose the spectral imaging method based on linear CCD,edge filtering method and Sagnac interferometry method as the demodulation scheme.The demodulated data is collected,stored and transmitted by data acquisition card and Field Programmable Gate Array(FPGA)development board.The design of upper computer is based on Lab VIEW,and the design of upper computer is based on Lab VIEW including data receiving,waveform display,storage and other additional functions.The main work of this paper is as follows:(1)This paper introduces different classification and application scenarios of FBG,analyzes the sensing principle of FBG,and the main demodulation methods of FBG wavelength,and explains their respective application scenarios and advantages and disadvantages.The fast demodulation scheme of FBG displacement sensor with wide dynamic range,synchronous measurement and high accuracy is selected.(2)The principle of FBG demodulation by Bay Spec's FBGA,low loss sawtooth filter and crossed Sagnac loop is analyzed.The FBGA module has short development cycle,high integration and strong expansibility.The design of low loss sawtooth filter uses the limited reflection virtual image array to replace the virtual image phase array,which reduces the optical loss.The system is smaller in scale,and can produce a sawtooth spectrum with a duty cycle of more than 70% and a period of about 1nm.The Sagnac loop produced has the property of continuous Gaussian shape,which can also realize the linear behavior and demodulate multiple fiber gratings with different wavelengths at the same time.(3)This paper introduces the advantages,application fields,development language and development process of FPGA development and design.The overall design of the development board is divided into three modules: acquisition module,storage module and transmission module.The expansion interface of the development board is combined with 50 MHz AD acquisition module to realize analog-to-digital conversion.DDR3 DRAM is used as data storage and serial port as transmission channel.The advantages,programming mode and development process of Lab VIEW are analyzed.The uploaded data is received through the configuration of dynamic link library or virtual instrument software architecture.(4)FBGA module,low loss dense array wideband sawtooth filter and crossed Sagnac loop are selected for demodulation system to tast micro-displacement sensor.The wavelength resolution of the three modules is about 1pm.The response frequency of demodulation system based on low loss dense array wideband sawtooth filter can reach 200 k Hz,which can realize the detection of high-speed vibration signal.Combined with Lab VIEW,the upper computer is developed to realize additional functions such as data receiving,waveform display and storage.