| Compared with traditional membrane gas meter,ultrasonic gas meter has the characteristics of high precision,wide range,low pressure loss and high intelligence degree,which has been gradually popularized and applied in the field of gas metering.However,the technical scheme of domestic ultrasonic gas meter mainly depends on foreign countries,the measurement accuracy and stability of the self-developed household ultrasonic gas meter needs to be improved.This paper aims to develop a household ultrasonic gas meter with high precision and low power consumption,by lots of tests and experiments,the performance of the gas meter is verified.Based on time difference method for the principle of flow measurement,the disadvantages of fixed threshold comparison method and the zero test in the ultrasonic echo signal detection are dissected.This article proposes a combinative way of threshold comparison and zero crossing detection to reduce the influence of environmental noise on ultrasonic wave propagation time by optimizing the theoretical zero crossing.At a large flow point,the amplitude of the ultrasonic echo signal attenuates severely,and the measurement accuracy of the ultrasonic gas meter is greatly affected by the gas flow rate.In order to solve this problem,this paper conducts design research on the installation method and installation angle of the transducer,it also proposes a way to compare the number of preset stop signals with the actual number of stop signals to achieve the change of threshold and gain.This method can not only reduce the influence of flow velocity on the accuracy of gas meters,but also obtain multiple ultrasonic propagation times by detecting an ultrasonic echo signal,decreasing the number of repeated measurements and system power consumption.This article analyzes and summarizes the shortcomings of moving average filtering and traditional Kalman filtering,and creates an optimized Kalman filtering algorithm to further improve measurement accuracy.The hardware circuit and software system of household ultrasonic gas meter are designed.In terms of hardware,low power consumption and high performance microprocessor chip MSP430F5438A is adopted.The design of ultrasonic signal transmitting and receiving circuit,amplifier circuit,high-precision timing chip circuit,analog switching circuit and other circuits are accomplished on the basic of this chip.In terms of software,the combination of timing interrupt and external interrupt is used,as the system monitoring mode,to divide and schedule the system tasks,so as to reduce the system power consumption.To verify the performance of ultrasonic gas meter,the ultrasonic gas meter prototype is tested according to the verification regulations.Experimental results show that the developed ultrasonic gas meter,in the range of 0.03～4 m~3/h range,can satisfy the ultrasonic gas meter verification regulation of 1.5 on the Richter scale accuracy requirements.With a capacity value of 6000 m Ah lithium batteries,it can work about 6 years,which basically meeting the enterprise’s requirements for long-term operation of gas meters without replacing batteries. |
