Study On Key Technologies Of Non-interventional Ultrasonic Liquid Level Measurement System

At present,most liquid fuels and liquid chemical gases used in industry are stored in a high-pressure closed container.In order to ensure the safety of production,the liquid level of the remaining liquid in these closed containers needs to be measured regularly during the production process.Because these liquids are flammable and explosive,the traditional liquid level measurement method will damage the tightness of the container,which is prone to liquid leakage and other safety accidents.In order to solve the above problems,a new non-invasive ultrasonic liquid level measurement system is designed by using the acoustic impedance characteristics of ultrasonic waves.On the basis of analyzing and comparing the common ultrasonic liquid level measurement principles,the paper determined to realize the liquid level measurement by using the change of ultrasonic impedance when ultrasonic wave propagated in different media,explained the sound field distribution when ultrasonic wave propagated in solid media in detail,expounded the change of echo sound pressure in different sound field areas,analyzed the change of echo energy of ultrasonic wave in a closed container,and determined the concrete realization mode of liquid level measurement according to the difference of echo energy at different positions above and below the liquid level.What's more,it analyzed the factors affecting the ultrasonic echo sound pressure energy and proposed the corresponding solutions from the measurement environment,the working frequency and diameter of the ultrasonic transducer and the coupling strength between the ultrasonic transducer and the measured container wall,and expounded the overall design scheme of liquid level measurement system combining with the principle of liquid level measurement.In the hardware circuit of the system,the ultrasonic transmitting circuit and ultrasonic receiving circuit with STM32 as the main control core were designed.As for the ultrasonic transmitting circuit,the working principle of the excitation signal bias circuit was expounded and the circuit output waveforms under different resistance and capacitance values were simulated and analyzed,which can realize the output of excitation signals with different amplitudes by using the amplifier with adjustable gain.In the aspect of ultrasonic receiving circuit,it expounded the working principle of peak detection circuit,analyzed the inert distortion of peak detection circuit by circuit simulation software,and explained the realization mode of echo acquisition module.What's more,it also described the design of the system power supply module.In the aspect of system software design,it expounded the filtering principle and implementation method of sliding filter,designed the judgment algorithm of liquid boundary and the approximation curve to judge the approximation degree of liquid level,implemented the data storage module by FLASH in STM32,and designed the control program of matrix keyboard.Finally,the liquid level measurement system designed in this subject was verified experimentally under different experimental environment conditions.The paper compared the variation trends of echo sound pressure at the two critical positions above and below the liquid level and at the liquid level under various measurement conditions,analyzed the problems existing in the experimental results and gave the specific solutions.