Research On The Method Of Ultrasonic Grout Density Measurement

As an important index of grouting technology,the high precision and real time measurement of grout density is of great significance.Traditional methods of grout density measurement are commonly used in conjunction with process design of whole grouting system,of which innovation are insufficient,and the accuracy also need to be improved.This paper presents a novel measurement method to realize high resolution(better than 0.01kg/m3)measurement of grout density with ultrasonic measurement technology and high-speed signal processing system based on FPGA.The density measurement is realized according to function relation between propagation velocity of ultrasonic wave and medium density,which means,density information of medium is obtained by detecting changes of ultrasonic wave velocity.When ultrasonic propagation distance is determined,propagation velocity can be obtained by precision measurement of ultrasonic wave propagation time in the medium,and then the density value can be obtained indirectly according to the propagation velocity.In this article,principle of ultrasonic grout density measurement is systematically analyzed,design of measurement scheme is completed,and feasibility of the method is verified by experiments.The core technology of ultrasonic measurement of grout density reflects in four aspects: multi-channel measurement structure,stable and reliable ultrasonic signal,high speed data acquisition system and special software algorithm.Designs of high speed hardware circuit based on FPGA and software based on Verilog HDL are the key to realize high precision measurement of grout density.As to the hardware design,FPGA is the core.It mainly includes drive circuit design of ultrasonic transducer and acquisition and processing circuit design of ultrasonic echo signal.The function of FPGA mainly reflects in three aspects,it combines with DDS technology to complete drive design of ultrasonic signal,with high resolution A / D conversion circuit to achieve high-speed sampling and storage design of ultrasonic echo signal,and the internally constructed processor can process sampling data stored in the RAM area.The software design includes design of echo data acquisition,characteristic wave search algorithm and high precision calculation algorithm of propagation time.Echo data acquisition is designed for the output signal of transducer receiver to develop an acquisition program.The acquisition data is stored in RAM which is built in FPGA.The characteristic wave search algorithm analyzes and compares the sampling data,so that the characteristic wave of maximum amplitude in echo signal is found.After the high precision propagation time algorithm determines the starting point and ending point of propagation time,use software interpolation algorithm to calculate ending time of propagation time.The experimental part,with pure water as under-test medium,aims to verify feasibility of density measurement scheme.Experimental results show that the measurement accuracy of ultrasonic propagation time is better than nanosecond level,which lays a foundation for development of ultrasonic grout density meter and realization of high precision measurement of grout density.