基于改进相差法的超声波微流量检测

Ultrasonic micro-flow measurement based on improved phase-difference method

针对传统超声波流量测量方法在微小流速工况下难以实现高精度测量的问题,提出一种基于计数器法与取样积分法相结合的改进相差法测量方法.首先采用高稳定性电子计数器实现整周期延迟相位粗测量,再基于取样积分原理实现剩余子相位的精细测量,通过增大取样积分次数抑制由抖动引起的相位差测量误差;同时通过移相控制,消除传统鉴相器具有的不稳定工作区的影响.仿真与实验结果表明:在DN20管道、常温纯水条件下,微小流量下测量最大相对误差小于1%,中、大流量的测量最大相对误差小于0.5%;在0.02 m3/h微流量点的测量标准差为86 cm3/h.改进相差法可实现比传统时差法更高的测量准确度和测量下限,有助于提高超声波在微流量条件下的检测性能.

To solve the precision measurement problem in micro flow condition of the conventional ultrasonic flow measurement method,an improved phase-difference method based on the combination of counter and sampling integration techniques is proposed.First,an electronic counter with high stability is adopted to realize the coarse measurement for whole cycle phase.And then the accurate measurement of sub-phase is achieved by using sampling integration technique which can greatly restrain the measurement error caused by jitter.At the same time,the dead zone of the phase detector can be eliminated by the phase shift control method.The simulation and experimental results show that under the condition of DN20 pipeline,normal temperature and pure water,the maximal relative error of micro flow measurement is less than 1%,while for medium and large flow measurements,the errors are both less than 0.5%,and the standard deviation is 86cm3/h at 0.02 m3/h flow point.The improved phase-difference method can achieve higher accuracy and lower limit than the conventional time-difference method.It is in favour of improving the ultrasonic testing performance in small flow condition.