Study On Hardware System Of Four-channel Gas Ultrasonic Flowmeter

Ultrasonic gas flowmeter has some advantages,such as high measurement accuracy,no pressure loss,large measuring range and suitable for large diameter pipes.However,The acoustic impedance of the ultrasonic transducer is greatly different from the acoustic impedance of the gas.This will lead to the transmittance very low and the amplitude of the ultrasonic echo signal very weak,,sometimes even submerged in noise,which will seriously affect the measurement accuracy and range ratio of ultrasonic gas flowmeter.from 2011 to 2014,our project group developed a double-path ultrasonic gas flowmeter,which achieved good results and meet the requirement for 1-level precision.In order to improve the measurement precision of ultrasonic gas flowmeter,the hardware system of four-path ultrasonic gas flowmeter based on a dual-core by a FPGA chip and a DSP chip was developed,and the strobe mode,transceiver mode,power supply,working mode of FPGA were in-depth study.The hardware system consists of transmitting / reception switching circuit the excitation signal generation and amplification circuit,echo signal conditioning and acquisition circuit,timing control and signal processing circuit,man-machine interface,serial communication and power circuit.In terms of excitation signal strobe mode,in order to realize the transition from low-side gating to high-side gating,improve the utilization ratio of the device,and reduce crosstalk between the channels,solid-state relay was used to replace the original FET to strobe the transmitting signal.In terms of transceiver mode,the simultaneous selection of two driving signals and receiving two echo signals,and the improvement of the high-speed DAC and high-speed ADC working mode were implemented to enhance the system's real-time performance and measurement accuracy of the instrument.With the improvement of FPGA operation mode and the use of Altera's fourth generation FPGA with TI's TMS320F28335,the drive control and data storage of high-speed DAC and ADC and digital signal real-time processing can be realized.Driving the eight transducers and storing the echo signal in sequence needs to be observed to shorten the working time of the whole process and improve the real-time performance of the system and the measuring accuracy of the instrument.In terms of power supply,in order to complete power supply design and meet the system requirements,the requirements for system power supply,power load capacity,voltage ripple and grounding technology were in-depth study.A measurement of gas flow can be achieved after completing the circuit design and the PCB layout of the hardware system,conducting the hardware debugging and the entire system debugging with the cooperation of the software.In order to verify the effectiveness of the system,the four-path ultrasonic gas flowmeter was calibrated in Chongqing science and technology test center.The calibration results show that the measurement accuracy of the four-path ultrasonic gas flowmeter is 0.2% and the repeatability is 0.04%,which is far superior to the "JJG1030-2007 Ultrasonic Flowmeter Verification Procedure" for the 1st-stage precision gas ultrasonic flowmeter.The results of the calibration have been fully recognized by the partner.