Development Of Low-power Gas Ultrasonic Flow Transmitter For High Pressure Resistant Transducer

Domestic membrane gas meters are mostly used for custody transfer measurement in some small-scale gas trade custody transfer measurement occasions,such as city gas,floor heating gas,small business gas,and coal-to-gas gas.Although the price of membrane gas meter is relatively low,it can only achieve level 2 or level 3 measurement accuracy,and the range is relatively narrow;at the same time,the measurement accuracy will decrease with the increase of use time.Therefore,low power consumption mono channel gas ultrasonic flowmeter is developed abroad to replace membrane gas meter and sold in China.But this kind of domestic gas ultrasonic flowmeter can not reach the corresponding technical indexes.Aiming at this situation,domestic high pressure gas ultrasonic transducers are selected.A digital signal processing method based on variable threshold is studied to solve the problem of low echo signal quality,and a low-power flow transmitter based on STM32 low-power microcontroller is developed.The hardware and software are optimized to achieve the 1.0 level measurement accuracy under the condition of mono channel gas ultrasonic transducer and battery power supply,and has passed the experiment test of the largest automation instrument enterprise in China.The experiment platform has been set up in order to test and analyze the echo signal characteristics of the domestic high pressure gas ultrasonic transducers.Due to the titanium alloy shell used in the production process of the high pressure resistant transducer,the acoustic impedance is not matched,which affects the quality of the echo signal,so that some commonly used digital signal processing methods are no longer applicable.Therefore,the digital signal processing method based on the variable threshold is studied to process the echo signal of the gas ultrasonic transducer and calculate the volume flow.The variable threshold signal processing method has a small fluctuation range of the maximum characteristic points in the range of 0 /??400 /?,so as to ensure the measurement accuracy.Besides this method is compared with the echo peak fitting method and the echo energy integration method to verify its superiority.Based on STM32 low-power microcontroller,the hardware part of the low-power gas ultrasonic flow transmitter is developed,which mainly includes an excitation circuit module,an echo conditioning module,a digital signal processing module,a communication module and a power management module.The circuit principle of each module is analyzed and the circuit parameters are calculated.In the design process,the power consumption of the system is reduced by selecting low-power devices and optimizing the circuit structure.The software part of the low power consumption gas ultrasonic flow transmitter is designed,which mainly includes an excitation generation module,an interrupt service module,a pulse upload module,and a low power consumption module.The working principle and steps of each module are analyzed,and the power consumption of the system is reduced by entering the stop mode through timing.The gas flow calibration experiments of sonic nozzle were carried out in Chongqing Chuanyi Automation Co.,Ltd.The calibration experimental results show that the indication error and repeatability of the developed gas ultrasonic flowmeter can meet the requirements of the national standard for the 1.0-level measurement accuracy under the condition of mono channel.The measurable flow range is 20 /??400 /?,and the turndown ratio is 20:1.