Design and Implementation of Ultrasonic Velocity Measuring Module Based on Phase-Locked Loop

Abstract

Due to the important relationship between ultrasonic velocity and some properties of sample, the measurement of velocity of ultrasound is widely needed in various fields. In this paper, based on phase-locked loop technique, a new hybrid circuit is designed for ultrasonic velocity measurement and named as UV-PLL. In order to improve the stability of phase and achieve the ability of fast locking, an auxiliary capturing circuit, which consists of phase shift circuit and capturing circuit, is designed and implemented in this module. Additionally, two methods for estimating the propagation delay is compared and described in detail. The UV-PLL module is validated through the ultrasonic velocity measurement in distilled water at different temperatures. Experimental results show that the maximum relative deviation of velocity measurement is less than 0.15% and the loop can be quickly locked, indicating that this module can meet the requirements of online measurement and can be widely applied. Index Terms—ultrasound, velocity, phase-locked loop (PLL), auxiliary capturing circuit, amplitude I. INTRODUCTION Due to its advantages of non-destruction, rapidity, accuracy and cheapness, ultrasonic testing has become a hotspot in the industrial inspection field. During the process of testing, a lot of interesting properties of sample are related to the ultrasonic velocity. Therefore, the ultrasonic velocity in specific sample is one of the most important parameters and how to accurately measure this parameter becomes the key problem in the whole inspection system (1, 2). Usually, the methods for acoustic velocity measurement can be classified into two categories. One is to acquire the velocity through