Study On Ultrasonic Measurement Model Of Liquid Density Based On Acoustic Impedance Method

Integrated electric propulsion system for ships is the forefront direction for the develop-ment of ship power. The research of battery energy storage technology and energy manage-ment mode is key technologies to develop energy storage module of IPS. In order to improve the efficiency and life of battery and to ensure reliable operation, the battery parameters need strict measurement to ensure a best working condition.Battery electrolyte is a kind of corrosive liquid, whose density is an important parameter to judge the battery charging and discharging state. The fast, accurate and online measurement for density of corrosive liquid is a problem for the development of this industry. This paper studies an ultrasonic measurement model of liquid density based on acoustic impedance me-thod, using the characteristics of fast response and nondestructive testing. The method treats the electrolyte as research object, and it is expected to achieve a fast, accurate and online measuring method for lead-acid battery parameters on ship. The research contents and achievements in this paper are as follows:(1) An ultrasonic impedance model of liquid density measurement is established, based on a basic hypothesis of ultrasonic plane wave. The model is in a symmetrical arrangement with double transducer and double buffer. One transducer acts as a transmitter and worked in pulse-echo mode, and the other operates in receiver mode. General expression of reflection coefficient at buffer-liquid interface is studied. According to the different combination of echo signals on two transducers, there are different methods to obtain the reflection coefficient.(2) An electrical-acoustic system equivalent model for ultrasonic propagation is estab-lished, based on the ultrasonic impedance model of liquid density measurement. The model uses the electric-machine-acoustic analogy method as a foundation to establish a lossy trans-mission line equivalent circuit of acoustic medium layer and controlled source and transmis-sion line equivalent circuit of piezoelectric layer. The acoustic characteristics and frequency and temperature dependent simulation parameters of piezoelectric ceramics, polymer and liq-uid are analyzed.(3) Based on the characteristics analysis of echo signals in simulation model, an ultra-sonic signal processing application architecture is studied. The signal is sampled at average mode and pretreated in sampling-filtering-extraction structure. The time domain cross-correlation function is used to analyze flight time and calculate sound velocity, and the l2-norm frequency domain integral method is used to analyze echo amplitude. The analysis and processing of ultrasonic digital signals and equivalent mathematical model is studied.(4) An experimental platform of ultrasonic measurement of liquid density is studied and established. The application configuration of measurement cell, uncertainty of liquid density, measuring quality evaluation method and system correction method are studied. The meas-ured results are analyzed.(5) A battery monitoring system on ship is designed using ultrasonic measurement model of liquid density. An on-line lead-acid battery monitoring system is used to achieve the real-time data acquisition and monitoring of battery operation parameters. The design of the lead-acid battery monitoring system is introduced in detail, and the measured results are ana-lyzed. The relative error of density measurement of the lead-acid battery monitoring system is less than0.5%, which meets the technical requirement of fast and accurate measurement.