Research On Key Technology Of High Precision And Low Power Ultrasonic Flowmeter

With the rapid population growth and the rapid development of global economy, the shortage of resources and pollution is becoming more and more obvious, especially fresh water resources and sewage discharge. Faced with the severe situation, governments take corresponding measures to deal with this problem, and it is urgently to adopt high-precision instrument for assurate measurement of liquid flow. Ultrasonic flow meter was born with simple measurement method and high accuracy, non-contact measurement. In recent years, the domestic and foreign research of ultrasonic flowmeter focuses on the high accuracy, high stability and low power. Based on the principle of time difference ultrasonic flowmeter, the key technology of high precision, low power was studied in the paper as follows:Firstly, by analyzing the status of fluid movement in the pipeline deeply, the average surface velocity correction factor was calculated to make flow rate closer to the true value and improve the measurement accuracy in laminar and turbulent flow condition. According to resonant characteristics of transducers and ultrasonic wave propagation properties, we proposed electric and acoustic matching about ultrasonic transducer. Because of the drive circuit, ultrasonic transducer work at resonance point to realize electrical matching. In the ultrasonic transducer, the plus damping block makes the crystal quickly return to resting state after oscillation starting. The sound and electric matching, the foundation of high accuracy measurement, can improve the stability of the ultrasonic signal.Secondly, according to ultrasonic flowmeter threshold and ultrasonic signal zero-crossing from the voltage amplitude fluctuations, we proposed the zero threshold smoothing models, which can effectively remove the interference signal before receiving the ultrasonic signal for the transducer. The measured results prove that this method can effectively restrain the static time difference change greatly and inhibit the static zero-point drift well. Based on 53H algorithm, the improved algorithm is proposed. A discrete curve smoothing is generated by measured time difference data. Then the actual measured value and the value of the estimated one is compared to identify outliers so that abnormal points are removed. Experimental results show that the actual results and simulation are consistent and measurement accuracy is improved well.Thirdly, based on analysis of power system, system power has been reduced by the choice of low power consumption chip, simplified data processing method, achieving time-sharing opening and closing of signal processing hardware circuit and MCU sleep mechanisms. Experiment results show that the method is feasible.Based on research of key technology time difference method ultrasonic flowmeter, the prototype was designed. The prototype was strictly tested on the basis of JJG 1030-2007 ultrasonic flow-meter standard. The measured results prove that the experimental prototype fully conforms to the standard.