Research On Automatic Calibration Method Inthe Thrust Testing System Of Rocket Engines

Thrust testing of rocket engines is an important part of rocket engine ground test.It is of great significance to study the attitude control of rockets.It is a critical link of the aerospace industry.Accurate calibration of force sensors is the basis of accurate thrust measurement.At present,thrust testing system on rocket engines are mostly using the static calibration in situ to do experiments.The static calibration method is complicated,time-consuming and it restricts the improvement of thrust measurement precision.Therefore,it is necessary to study the calibration methods of force sensors.In order to solve these problems,the static calibration method of force sensors is studied.In this paper,the thrust testing system of a large tonnage rocket engine is taken as the background,a kind of continuous calibration idea is proposed.The realization process is introduced,the equivalent mechanical model is established,and the factors influencing the continuous calibration accuracy are analyzed: the loading acceleration and speed of the force source,the sampling frequency and the experimental steps.The continuous loading calibration experiment system is designed and built,which includes large range hydraulic loading force source,force sensors,data acquisition card,data acquisition software and other components.Data acquisition software is compiled and developed by LabVIEW,including: system self-check,dynamic measurement,parameter setting,static calibration,automatic calibration,data retrieval,report generation and other functions.The experimental system has been tested and the performance is stable.The hydraulic automatic loading force source is designed,which can complete the automatic loading and unloading of one-way force.The function of this system in this paper has two parts:(1)Automatic calibration experiments of multiple groups of force sensors with different ranges were carried out on the system.The experimental results meet the 2% target,which proves that the automatic calibration method has practical value.And the experiments showed that the calibration accuracy of system output was not stable and reliable.(2)Analyzing and determining five influencing factors : the loading acceleration and speed of the force source,the sampling frequency,the experimental steps and the built-in error.They have great impacts on the calibration accuracy of the automatic calibration method.Five sets of comparative experiments were carried out on the system to explore how and to what extent they affected the calibration accuracy of the system.Finally,the best practicel ofthe automatic calibration system satisfying the two indexes of high calibration accuracy and stable service performance was determined.The system calibration solution was obtained through experiments: sampling frequency was selected as 5000 hz,sampling order was 6,the built-in error was set as 0.1%,and the calibration accuracy of the automatic calibration system met the index requirements when the force source was loaded slowly at a constant speed,the calibration effect was good.The stable output automatic calibration method is applied to the thrust testing system of rocket engines.The automatic calibration method is simple in operation,high in precision and valuable in research.