Research On Volume Measurement Technology Based On Micro Expansion

Volume is one of the important quantities of the vessel. Obtaining the volume of vacuum container with quick, accurate and non-destructive is the key link for accurately evaluating various physical parameters related with volume. There is abroad and important application value in the field of vacuum science and technology, such as vacuum leak detection, vacuum measurement, vacuum system design and calculations.A volume measurement method with strong applicability is proposed and researched in this paper. The principle of the method is to calculate the volume using the ideal gas equation and the small changes in pressure between the measured vessel of micro expansion and reference vessel with stable pressure. This method only produces relatively small volume change of the measured vessel during the measurement, and reduces thermal equilibration time of gas variable volume significantly, which can realize the rapid measurement of the volume of the vessel. The reference vessel as a pressure reference datum, and using a differential pressure sensor of smaller range measures the micro expansion generated pressure difference, accurate measurement of the volume of the vessel can be achieved. Moreover, since the micro expansion process produces only a slight variation of the gas pressure measured vessel, some specialized vessels can be non-destructive measurement. The detailed work is listed as follows:(1) Thermodynamic model and heat transfer model of the volume micro expansion process of the vessel are established. Researching the affecting factors of the system measurement time and measurement results. On this basis, the paper submits a comprehensive simulation model of spherical vessels and adiabatic expansion, and obtaining more conservative numerical simulation results of relaxation time of the volume measurement system. The paper submits the randomness unsteady heat transfer and porous media model based on the laboratory ambient temperature measurement data, and the constant voltage characteristic of the reference vessel of filled wire is simulated. Moreover, the effect of the ambient temperature on the background differential pressure of the system is researched.(2) Developed experimental system of the vessel measurement, and carried out a series of corresponding experimental studies. Based on the leakage detection of experimental system, the experiments of the background differential pressure, the repetitive experiments of the same volume and the experiments of different micro expansion volume are researched. Experimental results show that system measurement time is less than 40s under the expansion ratio of 0.4%～0.1%, of which relative error compared with the calibration results of water injection is less than 1%.(3) The source of uncertainty in the experimental system of volume measurement is analyzed, and the uncertainty of the measurement result is evaluated. Experimental results show that the standard uncertainty is 0.39%, and the expanded uncertainty is 0.78%(k=2).