Research On Key Technology Of New Liquid-level Sensor Based On Ultrasonic Impedance Method

The liquid fuel storage tank on the aerospace large-scale launch vehicle engine is a closed container with a large volume.Its interior is a high-pressure and low-temperature environment.The liquid fuel in the tank is usually flammable,explosive and corrosive.This brings difficulty to the measurement of the fuel level in the tank.At present,the commonly used sensors such as capacitors and floats sensors are large in size and weight,inconvenient for installation,and difficult to maintenance.During the process of rocket flight,they are disturbed by vibration and overload,and their safety and reliability are greatly affected.The non-contact liquid-level measurement scheme can avoid the above problems,and it has become one of the most promising technical schemes to solve this problem.This dissertation studied a non-contact liquid-level detection technology of fuel tank based on ultrasonic impedance method,developed a new type of ultrasonic Lamb waves sensor,and studied the key technologies in the sensors and liquid-level measurement system.The main research contents include:(1)Sensor liquid-level measurement principle analysis and key parameters research.Aiming at the sensor realization principle effectiveness and the influence rule of the main parameters,we studied the application of ultrasonic impedance method in liquid-level measurement.We analyzed the characteristics of ultrasonic Lamb waves sound field and its propagation theory,which provided a theoretical basis for the design of the sensor.We comprehensively studied the key parameters and influencing factors in the design of the new liquid-level sensor,including wafer material,diameter,natural frequency,ultrasonic buffer wedge material,wedge size,sound field characteristics,incidence angle of ultrasonic waves,dispersion characteristics and working mode of Lamb waves.According to the research results,we can determine the optimal parameters for the design of the new ultrasonic sensors.(2)Development and application characteristics of a new ultrasonic Lamb waves sensor.According to the optimal parameters,we designed a new type of ultrasonic Lamb waves liquid-level measurement sensor.We designed the transmitter and receiver peripheral control and signal processing circuits,and the volume of the designed sensor is 25×25×15mm,which have the characteristics of miniaturization and overload resistance.We studied the influence of ultrasonic excitation signal parameters on the measurement results,finally,±15V was selected as the voltage value of the excitation signal.We measured the dynamic characteristic parameters of the sensor,which meet ASTM-E1065 standard.Then we studied the influence of the installation distance between the transmitter and the receiver,so we can determin the optimal installation distance of the sensor.In addition,we also studied the effect of coupling agent on measurement in practical application.Seven commonly used couplant materials are selected from the fields of industry,medicine and aerospace.We studied the performance of ultrasonic energy transfer efficiency,acoustic impedance value,stability and temperature characteristics,and finally,the best coupling agent was determined as organic silica gel.This work completes the design of the sensor,determines other key parameters in use,and provides key test components for liquid-level measurement systems.(3)Optimization of new ultrasonic sensor data processing method and application research of liquid-level measurement.To solve the problems of data processing,error analysis and compensation when the sensor is integrated into the measurement system,we used the new ultrasonic Lamb waves sensors to measure the liquid level,and obtained the transfer function between liquid level and output voltage.We studied the static characteristic parameters of the sensor,such as range,linearity,sensitivity,hysteresis and repeatability.The results show that the maximum range of the sensor is 13 cm,and the repeatability and consistency are good.According to the nonlinear relationship between sensor input and output,we proposed a linearization optimization method,which solves the problem of segmental fitting of nonlinear data in practical applications,and reduces the error introduced by data processing.Verification experiments show that the method can reduce the average relative error by 3.87%,and the precision of liquid-level measurement is ?3.1mm.Then we studied the influence of temperature on the system,and gave a relationship of liquid level-temperature-output voltage(HTV)to compensate the system temperature.In addition,we also studied the relationship between the acoustic impedance,attenuation coefficient and other characteristic parameters of the measured object and the liquid levelvoltage polynomial coefficient,and established the relationship model between them-T matrix.It can be used to predict the influence of the characteristic parameter deviation of the measured object(non-uniformity,machining accuracy)on the precision of liquid level measurement.Finally,aiming at the measurement requirements of liquid-level in large containers in the aerospace field,using multi-sensor arrays,we give an array ultrasonic sensor liquid-level measurement solution,which realizes the real-time monitoring of dynamic liquid level,inclined liquid level and other complex situations.