基于全相位FFT超声波流量计的相位检测方法研究

Research on Phase Detection Method of Ultrasonic Flowmeter Based on All-Phase FFT

针对传统相位差法超声流量计在相位测量中易受外界干扰、准确度低的问题,提出了一种基于全相位快速傅立叶变换算法的超声波流量计相位检测方法。该方法由PLL时钟发生器产生两个频率相近的正弦信号分别用于激励与混频,并通过差频技术将混频后的参考信号与回波目标信号的相位信息从高频处理为低频信号,再由16位ADC对信号同步采样,超声波采样信号通过全相位预处理后进行FFT计算,得到准确的相位结果。同时,对比分析了全相位FFT的抗干扰性和采样频率对相位测量精度的影响,并将设计的电路应用于超声波液体流量测量,最终实验结果表明超声波流量计样机的测量误差优于1%,测量量程比为160∶1。

In order to solve the problems of the noises interference and the low accuracy in phase measurement of ultrasonic flowmeter,a phase detection method of ultrasonic flowmeter based on all-phase FFT algorithm is proposed. In this method,PLL clock generator generates two sinusoidal signals with similar frequency,which are respectively used for excitation and mixing. The phase information of the reference signal and echo target signal after mixing is processed,and the signal is transform from high frequency to low frequency signal by differential frequency technology. Then the signal is sampled synchronously by 16 bit ADC. The ultrasonic sampling signal is processed by FFT after all-phase preprocessing and the accurate phase is obtained. At the same time,the anti-interference of all-phase FFT and the influence of sampling frequency on the phase measurement accuracy are compared and analyzed. The designed circuit is applied to ultrasonic liquid flow measurement. Finally,the experimental results show that the measurement error of the ultrasonic flowmeter prototype is better than 1% and the measurement range ratio is 160∶1.