Volume Measurement Method Using A Constant Conductance Element

Volume measurement has significant application value in the fields of vacuum science,space exploration,petrochemical,trade and transportation.There are issues in the traditional methods,such as the complex and time-consuming measurement process,high instrument cost,low precision,and so on.The paper reports a new volume measurement method based on a constant conductance element,which can be used to measure the container volume directly.The container to be measured is connected to the reference environment with constant pressure via the AAO leak element.The dynamic differential pressure decay between the inlet and the outlet of AAO leak assembly is measured and fitted by an exponential function of the experimental time and the conductance of AAO,followed by volume calculation based on the function.In order to select the appropriate conductance,the CFD simulation analysis of the internal temperature fluctuation of the container under different gassing rates is carried out.Combined with the precision of the experimental instrument,the AAO constant conductance element is designed and fabricated,and the conductance measurement system based on the flow method is constructed.The conductance of nitrogen,helium and argon flowing through the AAO element is accurately measured,which fully conforms to the molecular flow characteristics of the constant conductance,and the uncertainty is 0.38%.Then the volume measurement system is constructed,including AAO packaging cell,hardware and software system of data acquisition.The mean filtering method is used to optimize the acquired data.Under the condition of vacuum as constant pressure environment,the volume measurement of two kinds of containers was carried out by the measurement system.The corresponding measurement results of three experimental gases(nitrogen,helium and argon) were validated against the water injection method with estimation error less than 0.51%,and the volume measurement uncertainty didn't exceed 0.064%.In order to expand the application range of the measurement method,the measurement device has been slightly modified,and the volume of the container was measured under the condition of atmospheric pressure as a reference environment,and the relative error was less than 0.83% compared with the water injection method,which verified the effectiveness of the measurement method under atmospheric pressure.The results indicate that the volume measurement proposed in this paper is able to obtain the volume of the containers with high precision,high efficiency and simple facilities.It does not need to consider the heat balance time during measurements.The container can be measured using a variety of gases,near vacuum or atmospheric pressure.