Design Of Coherent Doppler Flowmeter Based On EtherCAT Bus

Doppler flow velocity measurement is one of the most commonly flow velocity measurement methods,and its application is more and more extensive.In order to speed up the calculation of Doppler flow velocity,improve the stability of the system and ensure the real-time performance of the data,this paper proposed a Doppler flow velocity measurement method based on EtherCAT communication technology and FPGA technology.In order to reduce the echo error,increase the signal emission energy and reduce the energy dissipation of the ultrasonic wave in the water,the two-phase modulation of the sine wave generated by DDS is used as the transmission signal.The sine wave is subjected to two-phase modulation using a 5-order sequence,and the center frequency of the transmitted signal is 2 MHz.EtherCAT communication technology has been used in the paper,which can provide high efficiency transmission technology and guarantee real-time feature.Based on FPGA chip to build hardware circuit,to use of FPGA manufacturers' rich IP core resources,can maximize the streamlined hardware circuit,and reduce design difficulty.In this paper,we first introduce and review the development of ultrasonic flowmeter at home and abroad,and understood that the use of Doppler flow velocity measurement has become one of the trends of current measurement method.The basic principle of Doppler flow measurement is summarized.Since the Acoustic Doppler Velocimetry designed in this paper is mainly used in coastal and laboratory environments,the coherent flow measurement method is adopted.Based on this,the time domain phase estimation algorithm as the echo processing algorithm of this paper,thus reducing the computational complexity and improving the calculation accuracy.Use XC3S400 chip as a control chip.In the design of the transmitter circuit,use AD9708 DAC chip to convert digital signal to analog signal.And then the analog signal through the two-stage amplification,so that the peak-to-peak transmission signal to meet the requirements of the transducer,detailing the first-order amplification and secondary amplification circuit design.The transmitted electrical signal is converted into an acoustic signal through the transducer and emitted,and the classification and design of the transducer are described in the paper.The ultrasonic echo signal carries the Doppler shift information back to the transducer,and the transducer converts the acoustic energy into electrical energy.In this paper,the application of low pass,high pass and bandpass filter is described.The design method of broadband bandpass filter and narrowband bandpass filter is introduced.The circuit design of narrowband bandpass filter is described in detail.The echo signal passes through narrowband Bandpass filter,which can effectively remove clutter and white noise,thus contributing to the effective signal extraction.After the echo signal is processed by the FPGA,the data is transmitted to the master station of the PC using EtherCAT communication technology.Finally,the proposed method and design are verified by experiment and simulation.The experimental results show that the proposed method and design not only have lower experimental error but also have high reliability.