Design Of Electric Wave Velocity Meter

China's environment is complex and water resources are insufficient.It is very important to study the variation regularity of river velocity and to carry out accurate hydrological monitoring,which is helpful to the rational and efficient development and protection of water resources.Hydrological monitoring of water flow measurement is very important,and flow measurement is an essential part of flow measurement.In this paper,the design of the radio wave velocity meter is a non-contact flow measurement instruments,compared to the traditional contact flow meter with simple operation,high accuracy and other advantages.According to the Doppler effect,the velocity sensor emits electromagnetic waves.The Doppler frequency shift is caused by the flow of the water.The frequency-shift signal contains the information of the water surface velocity,which can be obtained by analyzing the signal frequency.This design uses Cortex-M4 core ARM microprocessor STM32F407VGT6 as the control and signal processing core to complete the system hardware and software design.Hardware circuit system includes main control module,speed measurement module,signal acquisition module,storage module,man-machine interface design and communication module.Tachometer module uses radar sensors to transmit and receive electromagnetic waves,and through the internal processing of radar sensor to get the final Doppler frequency shift,namely the radar difference frequency signal.Acquisition module is mainly used to enlarge the radar differential frequency signal,identify the direction of the water flow,and implement the digital-to-analogue conversion.Storage module is designed to store the instrument parameters and measurement data.The man-machine interface design includes the buttons and demonstration.This design has five keys,through which we can set the instrument installation angle,record the time interval,display the inputted orders and so on.In order to improve the instrument's openness,the communication module is extended by a RS-485 interface.According to the hardware design,write each module's driver programming to achieve the function of every module.In order to improve the measuring accuracy of the instrument,when the digital signal processing of radar difference frequency signal is processed,FIR filter is designed to reduce the noise of the system by digital filtering.When the frequency estimation is carried out,the energy centro-baric method is used to correct the frequency of the radar differential frequencysignal to improve the frequency measurement precision.After above-mentioned processes,the precise frequency of the radar difference frequency signal is obtained.And then according to the principle of electromagnetic wave velocity meter,the water surface flow rate can be calculated.Verify the feasibility and accuracy of the speed-measuring algorithm by MATLAB software.After field testing,the wave current meter designed in this paper can accurately measure the surface velocity and run well,which fully proved the system feasibility and stability.