Design And Implementation Of Displacement Tag Reader

Large buildings such as bridges,dams,tunnels and other large buildings play an increasingly important role in modern society.In the process of construction and long-term use,the small deformation or displacement may gradually accumulate due to the influence of various internal and external forces.When the deformation or displacement exceeds the threshold value that the building can withstand,it might collapse,directly threaten the safety of people’s lives and property.So there is an urgent need to develop a new deformation monitoring system,which has these advantages such as real-time,high precision,high reliability,convenient installation.This kind of deformation monitoring system will give accurate feedback of the displacement information of the building,so that people can take timely measures to prevent serious collapse accidents.Based on the microwave phase comparison measurement,this paper researches a new monitoring method,which is composed of displacement tag reader and displacement tag.The system can realize multi-point displacement measurement and has many advantages,such as easy to install,high precision,low hardware cost.When the system is working,the radio frequency carrier signal from the tag reader is transmitted to the several displacement tags on the target building.The displacement tag produces different frequency sine waves signal,then modulates it to the received frequency carrier signal and retransmit the modulated signal to the displacement tag reader.The tag reader collects the mixed signal and then down converted to the baseband.Each monitoring point tag is distinguished and extracted by tag separation module in tag reader.The carrier phase difference between the displacement tag and the tag reader can be calculated by phase detection module.The change amount of phase difference is proportional to the amount of displacement tag.This paper analyzes the displacement tag reader in the measurement system and mainly researches the scheme design of the displacement tag reader,the establishment of experimental verification platform,the implementation of software programs,and design of leakage cancellation circuit.The main research contents are as follows:(1)The paper first analyzes the basic principles of the measurement system which is consisted of displacement tag reader and displacement tags.The method is based on the microwave phase comparison technology,which can complete the simultaneous measurement of multiple monitoring points and have high precision.(2)The experimental verification platform of displacement tag reader is set up.The scheme design of displacement tag reader is analyzed,and the function design and signal processing flow path of transmitter and receiver are discussed.Experimental verification platform adopts zero IF transceiver AD9361 as the transceiver channel and ARM/FPGA as the data processing module.(3)The software program of displacement tag reader is designed.ARM software was designed to configure the relevant registers of AD9361,and FPGA software was designed to generate analog tag signal,process received signal and calculate the displacement.(4)The leakage cancellation circuit in displacement tag reader is researched.If the amplitudes of the two signals are equal and the phases are opposite,then the sum of these two signals is zero.According to the idea,three schemes of leakage cancellation scheme are analyzed,and the scheme based on amplitude phase module is designed,which can effectively suppress the leakage signal existing in the tag reader.Experimental results show that the designed displacement tag reader can achieve high precision displacement measurement.The leakage cancellation circuit based on amplitude phase module can effectively improve the performance of the measurement system.