Signal processing issues on time-of-flight estimation by correlation in transit time ultrasonic flow measurement are discussed, including the position of the envelope extraction and the ambiguity problem when searching the correlation peak. The realistic flow experiments are conducted on the air flow experimental facility to compare the pre-correlation-envelope-extract-ing (PRCEE) method with the post-correlation-envelope-extracting (POCEE) one. The results show that the average reading error of the flow rate obtained by POCEE is about half of that obtained by PRCEE and the standard deviation is about 1/3, as it takes advantage of the fine structure of the carrier and makes full use of the signal information. Moreover, the probability distribution of the correlation peaks is given. And the time gating at peaks as well as the temporal/spatial median filtering is introduced to solve the ambiguity problem of correlation peak search. With the nonlinear processing techniques, the reading error of flow rate at 18. 9 m/s reduces from 30% to 3. 3% and the standard deviation from 2 m/s to 0. 35 m/s.%传播时间法超声流量测量中使用相关时延估计,需考虑包络提取位置和相关峰值模糊性问题.在标准表法空气流量实验装置上,进行了相关前/后包络解调和相关峰值检测概率分布的实验.结果表明,先相关后取包络,可充分利用载波的精细化结构和较完整的信号信息,流速的平均读数误差约为先取包络后相关方法的1/2,标准偏差约为其1/3.峰值模糊性导致较高流速时(18.9m/s),最大误差达30％,标准偏差2 m/s,引入适当的非线性处理技术,如加窗峰值搜寻和时间/空间中值滤波,上述指标分别降至3.3％和0.35m/s.
展开▼
