Research on a transit-time liquid ultrasonic flowmeter under unstable flow fields

Abstract

A transit-time ultrasonic flowmeter calculates a flow rate by measuring the transit time of the ultrasonic signal. In flow measurement, there are energy attenuation and noise interference, and sometimes the ultrasonic signal will fluctuate or even distort, which makes it impossible to find the reference position and obtain the correct transit time under unstable flow fields. Therefore, based on the mathematical model of the ultrasonic signal, the characteristics of the peak ratios of adjacent peaks in the ultrasonic signal are studied, and a peak ratio matching method-based signal processing method is proposed for ultrasonic flowmeters. Firstly, through the analysis of signal quality, a standard peak ratio array is set up, then the peak ratios are calculated to obtain a real-time peak ratio array in the flow measurement, and finally a matching algorithm for elements in the standard peak ratio array and elements in the real-time peak ratio array are used to find the reference position. The transit time of the ultrasonic signal can be obtained by the reference position and positive zero-crossing points. The signal processing method is implemented in real time in the system where a time-to-digital converter timing module is used to measure zero-crossing times, an analog-to-digital converter sampling module is used to sample the ultrasonic signal at the same time, and two STM32 (32-bit ARM Cortex-M Microcontroller) processors are used to analyze the signal quality and data processing. The effectiveness of this signal processing method is verified by a large number of experiments.