Hydrophone Sensitivity Measurement System Design Using Pulse Method

Hydrophones are widely used in hydroacoustic measurements,but their sensitivity needs to be calibrated before use,and calibrating large quantities of hydrophones using traditional calibration methods can consume a lot of staff time and effort.Based on the calibration principle of comparative method and pulse method,this paper designs a measuring system that can perform hydrophone sensitivity calibration in both air and water.This system is used in the air to quickly and roughly measure a large number of hydrophones,screen out a batch of hydrophones with normal sensitivity,and then in the anechoic pool,the system is also used to carry out more accurate measurement and calibration,which can greatly improve work efficiency.According to the overall design requirements of the calibration system,the hardware system is divided into three modules: digital-to-analog conversion module,signal acquisition module and digital control module.The digital-to-analog conversion module is responsible for generating pulse signals with adjustable amplitude,frequency,and pulse width.The signal acquisition module has four acquisition channels,which are responsible for realizing signal conditioning,signal acquisition and other functions.The digital control module is responsible for realizing the control functions of the log-to-analog conversion module and the signal acquisition module.The main control chip FPGA of the digital control part adopts the USB2.0interface with the host computer to complete two-way communication.This set of system software design includes FPGA program design and host computer display control software design,FPGA program includes ADC analog-to-digital conversion process,USB Slave FIFO asynchronous read and write process,analog switch on-off process and DAC digital-to-analog conversion process,by analyzing the instructions of the host computer to start signal generation,signal acquisition,data upload and other work.As the window for the user to control the entire system,the display and control software of the host computer processes the collected data and plots it into a sensitivity level curve,and calculates and displays the calibration results of the hydrophone to be measured in real time.Test the functions and important indicators of each module,including the amplitude consistency of each channel,equivalent input noise,isolation between channels,data transmission rate,etc.The test results of each module function normally,and the indicators meet the requirements.The system was handed over to the transducer development team for use,and field experiments were carried out many times on the anechoic tank and Hangzhou Xin’an River,and the sensitivity calibration of B&K’s 810 x series hydrophones and 140 selfdeveloped hydrophones was carried out in the range of 500Hz-10 k Hz.After comparing and analyzing the calibration results of each hydrophone and the calibration results given by the measurement unit after sampling and testing,it is concluded that the error of the measurement result of this system is about 2d B in air and about 1d B in water.Tests over a long period of time have shown that the calibration system works reliably and reliably.