Automatic tracking method of reference waveform of mine ultrasonic gas flowmeter
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摘要: 为了提高矿用超声波气体流量计的准确性，针对互相关检测信号存在“跳波”现象并影响超声波渡越时间测量精度的问题，提出了一种矿用超声波气体流量计参考波形自动跟踪方法。在计算超声波渡越时间的同时，对超声波参考波形和实时接收信号波形进行互相关运算，并计算互相关检测的可信度，设定可信度有效阈值和参考波形更新阈值，对互相关系数进行可信度评审，判定参考波形是否更新。可信度小于有效阈值时，判定接收信号无效，重新发送超声波信号；可信度大于更新阈值时，判定接收信号波形与参考波形高度吻合，不需要更新参考波形；可信度介于有效阈值与更新阈值之间时，判定接收信号有效，用当前接收信号波形替换原参考波形，实现参考波形自动跟踪。分析了可能造成超声波渡越时间差错1个波形周期的2种超声波接收信号波形变化：包络连续形变和包络瞬间畸变。气体流速、温度、压力的变化会导致接收信号包络发生连续性变化；尖峰脉冲、随机信号和周期干扰等可能导致超声波接收信号包络发生瞬间畸变，包络瞬间畸变可分为主峰严重畸变、主峰微小畸变、非主峰畸变3种情况。试验结果表明，在不同流速、温度、压力、噪声影响下，超声波气体流量计的相对误差不超过±1.0%，满足精度1.0级测量要求，参考波形自动跟踪方法为流量测量的准确性和可靠性提供了保障。Abstract: The accuracy of mine ultrasonic gas flowmeter needs to be improved. The cross-correlation detection signal has 'signal hopping' phenomenon and affects the measurement precision of ultrasonic transit time. In order to solve the above problems, this paper proposes an automatic tracking method of reference waveform of mine ultrasonic gas flowmeter. While calculating the ultrasonic transit time, the cross-correlation operation is carried out between the ultrasonic reference waveform and the real-time received signal waveform. The reliability of the cross-correlation detection is calculated. The reliability effective threshold value and the reference waveform update threshold value are set. The reliability of the cross-correlation coefficient is evaluated so as to determine whether the reference waveform is updated. When the reliability is less than the effective threshold, it is determined that the received signal is invalid, and the ultrasonic signal is re-sent. When the reliability is greater than the update threshold, it is determined that the received signal waveform is highly consistent with the reference waveform. There is no need to update the reference waveform. When the reliability is between the effective threshold and the update threshold, it is determined that the received signal is valid. And the original reference waveform is replaced with the current received signal waveform to realize automatic tracking of the reference waveform. This paper analyzes the two kinds of waveform changes of ultrasonic received signal which may cause ultrasonic transit time error of one waveform period. The waveform changes are continuous envelope deformation and instantaneous envelope distortion. The change of gas flow rate, temperature and pressure will lead to the continuous change of received signal envelope. Spike pulses, random signals and periodic interference may cause instantaneous envelope distortion of the ultrasonic received signal. The instantaneous envelope distortion can be divided into three cases, severe distortion of the main peak, slight distortion of the main peak and non-main peak distortion. The experimental results show that under the influence of different flow velocity, temperature, pressure and noise, the relative error of ultrasonic gas flowmeter is less than ±1.0%. The results meet the measurement requirement of precision level 1.0. The automatic tracking method of reference waveform provides a guarantee for the accuracy and reliability of flow measurement.
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图 2 不同流速下超声波接收信号包络分布
Figure 2. Envelope distribution of ultrasonic signals at different velocity
图 3 不同温度下超声波接收信号包络分布
Figure 3. Envelope distribution of ultrasonic signals at different temperature
图 4 不同压力下超声波接收信号包络分布
Figure 4. Envelope distribution of ultrasonic signals at different pressure
表 1 不同流速下流量计试验数据
Table 1. Experimental data of flowmeter at different velocity
参考流速/
(m·s−1)参考流量/
(m3·h−1)实测流量/
(m3·h−1)相对
误差/%可信度
最小值参考波形 0 0 0 0 0.97 未替换 0.500 56.55 56.579 0.37 0.91 未替换 0.986 111.56 112.029 0.42 0.86 未替换 2.990 338.21 340.003 0.53 0.81 未替换 7.986 903.19 909.693 0.72 0.71 替换过 11.971 1 353.90 1 357.982 0.30 0.67 替换过 20.914 2 365.37 2 357.091 −0.35 0.64 替换过 30.605 3 461.40 3 431.632 −0.86 0.63 替换过 
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表 2 不同噪声影响下流量计试验数据
Table 2. Experimental data of flowmeter at different noise
噪声
类型参考流量/
(m3·h−1)实测流量/
(m3·h−1)相对
误差/%可信度
最小值参考
波形无噪声 111.56 112.029 0.42 0.86 未替换 噪声① 111.56 112.102 0.49 0.82 未替换 噪声② 111.56 112.113 0.50 0.81 未替换 噪声③ 111.56 112.108 0.49 0.76 替换过 噪声④ 111.56 112.201 0.57 0.73 替换过 噪声⑤ 111.56 112.123 0.50 0.75 替换过 噪声⑥ 111.56 112.216 0.58 0.63 替换过 噪声⑦ 111.56 112.413 0.76 0.52 失效过
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表 3 不同温度下流量计试验数据
Table 3. Experimental data of flowmeter at different temperature
温度/℃ 可信度
最小值参考
波形温度/℃ 可信度
最小值参考
波形−20 0.97 未替换 30 0.78 替换过 −10 0.90 未替换 40 0.75 替换过 0 0.86 未替换 50 0.74 替换过 10 0.83 未替换 60 0.71 替换过 20 0.81 未替换
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表 4 不同压力下流量计试验数据
Table 4. Experimental data of flowmeter at different pressure
压力/kPa 可信度最小值 参考波形 压力/kPa 可信度最小值 参考波形 40 0.75 替换过 90 0.86 未替换 50 0.76 替换过 100 0.91 未替换 60 0.79 替换过 125 0.91 未替换 70 0.81 未替换 150 0.91 未替换 80 0.83 未替换
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