Research And Implementation Of Multi-point Displacement Measurement Method Based On FDMA And TDMA

It has always been a focus of attention for people to conduct research on deformation monitoring of bridges,dams,and other buildings.Displacement of bridges,dams,and other buildings mainly refers to deformations that occur due to external forces after completion.These deformation variables increase over time.If the building is not maintained for a long time,it will lead to qualitative changes and then cause major accidents when the external force cumulatively exceeds the limit.Research on deformation monitoring of bridges,dams,and other buildings is of great significance.The patent "A Micro-Displacement Measurement System" proposes a micro-displacement measurement method based on the technology of comparing microwave phase,which can realize the measurement of tiny displacements of bridges,dams,and other buildings.This method can achieve all-weather,automated and high-precision measurement,but only one target point displacement can be measured at a time.It is often necessary to perform displacement monitoring on multiple target points for some large-span bridges,high-rise buildings and other large buildings,but this method is difficult to meet requirements.In order to meet the demand of multi-displacement measurement in buildings,this thesis proposes two methods that multipoint displacement can be measured based on FDMA and TDMA,which based on the technique of comparing microwave phase.The method of multipoint displacement measurement based on FDMA adopts the idea of frequency-division multiple access to apply the displacement measurement of multiple targets.Different target points can be automatically distinguished and measured synchronously according to the different frequency of the signal of target,it is suitable for the dynamic measurement of bridges,dams and other buildings.However,it consumes a lot of channel resources.Each target point needs a separate channel,which will greatly increase the cost of hardware.The method of multi-point displacement measurement based on TDMA adopts the idea of time division multiple access to realize the displacement measurement of multiple target points.According to the conclusion that the phase difference of the two double-sideband modulated signals in the same observation point signal is the initial phase difference of the carrier signal,it can achieve automatic discrimination of multiple target points.The multi-point displacement measurement based on TDMA is suitable for static measurement of buildings such as bridges and dams.This method can save more channel resources.It only requires two channels to complete automatic measurement of multiple target points,but it cannot achieve synchronous measurement of multiple target points.The entire measurement system consists of two parts: beacon and its transmitting channel,receive channel and its receiving data processing terminal.The STM32 controls the AD9959 to generate the required IF signal and tag signal in the beacon.The tag signal is a single-frequency cosine signal which can achieve multi-target signal frequency division.The analog multiplier AD835 is used for double-sideband modulation.The transmitting channel up-converts the measurement signal to the RF 5.8 GHz and transmits it by the antenna;The receive channel receives the RF signal and down converter transfer the signal to 1 MHz.The receiving data processing terminal collects the signal and performs signal processing.The receiving data processing terminal includes the acquisition card and OMAPL138.The acquisition card acquires data and after the down frequency conversion processing,then sends the data to the DSP of the OMAPL138 through an EMIFA interface.The DSP performs arithmetic operations to obtain the observation point target displacement value,and sends the data to the ARM terminal through dual-core communication.The ARM terminal receives the data and displays it in the graphic interface.At the same time,the GPRS module uploads the data to the web server to store the data.