Research On Multi-path Ultrasonic Open Channel Flow Measurement Method Based On GPS Synchronous

Because of its simple structure,non-contact measurement and easy to realize integration,ultrasonic flowmeter has great application value and wide application prospect in the fields of industrial and agricultural production,medical detection and environmental monitoring,involving the quantification and measurement of gas or liquid.In this paper,aiming at the special measurement object of open channel flow,a multi-channel ultrasonic flow measurement system based on GPS synchronization is designed for wireless flow measurement.Based on the principle of time difference method,aiming at the shortcomings of the common open channel flowmeter,such as the small number of channels and the long cable,a wireless flow measurement method is proposed,which combines the GPS high-precision second pulse synchronous single chip microcomputer with the wireless serial port module based on Lora protocol.The Moving sine-wave fitting algorithm is designed to analyze and process the ultrasonic sensor signal directly,and get the time-of-fight accurately.The necessary hardware and software design of the system is given.The main research contents are as follows:First of all,the measurement principle of multi-channel ultrasonic flowmeter and the derivation of relative formula of velocity measurement by time difference method are introduced in detail,and the overall scheme design of multi-channel ultrasonic open channel flow measurement system based on GPS second pulse synchronization is proposed.Secondly,the hardware circuit of the measurement system is designed,which mainly includes the selection of STM32 single-chip microcomputer and the introduction of the internal module functions,the design of ultrasonic transmitting circuit,ultrasonic receiving circuit,channel switching circuit,voltage stabilizing circuit,peripheral module circuit and the selection of the chips involved in the system.Thirdly,the whole measurement system is divided into two parts: the host computer and the lower computer.The host computer is responsible for displaying measurement data,sending communication instructions and other functions.The lower computer cooperates with the channel switching circuit according to the Remainder algorithm to solve the problem that the channel switching is difficult to synchronize when multi-channel flow measurement is conducted.The transmission format of the communication instructions of the related system is designed to make the communication between the host computer and the lower computer more coordinated,so as to ensure that the lower computer can accurately and quickly execute the related functions according to the relevant command numbers in the transmission instructions.The magnitude of the flow is obtained by calculating the time-of-fight difference with the Moving sine-wave fitting algorithm,which improves the measurement accuracy of the system under the condition of meeting the requirements of real-time signal processing.Finally,the measurement system is tested.After debugging each module,the parameters of the relationship between the time-of-fight and the sampling sequence value of absolute feature points obtained by the Moving sine-wave fitting algorithm are determined through the calibration test,which determines the basic parameters for the subsequent measurement.The measurement accuracy of multichannel measurement is 76.47% higher than that of mono measurement,which proves that the multichannel measurement system can significantly reduce the measurement error.The measurement accuracy of multichannel measurement system is 0.324m3/h.Finally,some methods to reduce the measurement error are given.