基于超声波时差法的管道流量测定仪设计

煤矿现有抽采管道使用传统瓦斯流量计存在易产生堵塞故障等问题,基于超声波时差法的流量计测量精度高、测量结果重复性好,但不适用于瓦斯抽采管道流量测量,并且需要单独设计超声波驱动电路和信号处理电路,实现难度较大。针对煤矿瓦斯抽采管道的特点,设计了一种基于超声波时差法的管道流量测定仪。在固定的传播距离下,超声波换能器发出的超声波在流体中的传播时间与气体的流速呈函数关系,而流速与管道截面积的乘积即为流量,从而间接得到管道气体流量。该管道流量测定仪以低功耗微处理器STM32F103为核心控制元件,在时间数字转换芯片MAX35104内部通过自动差分飞行时间测量法计算超声波顺逆流传播时间,根据传播时间计算气体流速、瞬时流量和累计流量。测试结果表明,基于超声波时差法的管道流量测定仪的最大绝对误差为0.15 m/s,最大重复性误差为0.17%,符合JJG 1030—2007《超声流量计检定规程》中2级精度要求,同时也满足MT 448—2008《矿用风速传感器》中对超声波式风速传感器基本误差的要求。

Design of pipeline flow meter based on ultrasonic time difference method

The traditional gas flow meter used in gas pipelines in coal mines has problems like blocking failure.The flow meter based on ultrasonic time difference method has high measurement accuracy and good repeatability of measurement results.However,it is not suitable for gas extraction pipeline flow measurement.Moreover,it is difficult to design ultrasonic driver circuit and signal processing circuit separately.Based on the characteristics of coal mine gas extraction pipelines,a pipeline flow meter based on ultrasonic time difference method is designed.In the context of fixed propagation distance,the propagation time of ultrasonic waves emitted by ultrasonic transducer in the fluid is functionally related to the gas flow rate.The product of the flow rate and the cross-sectional area of the pipeline is the flow,hence the pipeline gas flow is indirectly obtained.The pipeline flow meter uses a low-power microprocessor STM32F103 as the core control element,and uses the automatic differential flight time measurement method inside the time-to-digital conversion chip MAX35104 to calculate the ultrasonic wave downstream and upstream flow propagation time.The gas flow rate,instantaneous flow and cumulative flow are calculated through the propagation time.The test results show that the maximum absolute error of the pipeline flow meter based on ultrasonic time difference method is 0.15 m/s and the maximum repeatability error is 0.17%.The performance meets the requirements of level 2 accuracy in JJG 1030—2007 Verification Regulations Ultrasonic Flowmeters and also meets the requirements of the ultrasonic wind speed sensor basic error requirements in MT 448—2008 Wind speed sensor for mine.