Research On Mechanical Characteristics Of Pressure Sensing Diaphragm Of Capacitive Diaphragm Vacuum Gauge

Vacuum science and technology have been rapidly developed and widely used since the 20th century.The measurement of vacuum degree is an important part of vacuum science and technology.Accurate measurement of vacuum degree and control of the level of vacuum degree has significant impact on industrial production and scientific research,which plays a key role in the quality of vacuum products.With the development of China’s aerospace industry,in-depth space exploration activities has vital strategic influence to the development and advance of the nation,which has put forward new standards and requirements for the measurement of space vacuum degree.As it is almost impossible to directly measure tiny pressure under current vacuum measurement technology,it is common to make certain physical phenomenon of the gas to measure real pressure.Capacitive diaphragm vacuum gauge is a kind of vacuum instrument that can be used as a reference standard for low-vacuum measurement,which is the only one internationally recognized.With the characteristics such as small size,light weight,high accuracy,good linearity and fast response,capacitive diaphragm vacuum gauge is broadly applied in the fields like meteorological monitoring,chemical production,military de fense and scientific research,which is significant to China’s space exploration.It is the key aspect to realize independence and controllability of core vacuum instruments to perform independent research and development of capacitive diaphragm vacuum gau ges.This paper studied mechanical properties of the pressure sensitive diaphragm of the capacitive diaphragm vacuum gauge.Based on the theory of elastic mechanics and Von Karman’s large deflection mathematical model,the finite element model of pressure sensing diaphragm of capacitive diaphragm vacuum gauge was set up using ANSYS,and simulation calculation was performed.The impacts of material,structure size and pre-tension of pressure sensitive diaphragm on the mechanical properties of the diaphragm were analyzed.The main conclusions are:（1）The largest deflection of the pressure sensing diaphragm is at the center of the diaphragm,and the smallest deflection at the edge of the diaphragm.The deflection gradually increases from edge to the center of the diaphragm in radial direction.The central deflection of the diaphragm increases with the increase of the uniform load,and the extent of increase recedes.The maximum stress value of the pressure sensing diaphragm is at the edge of the diaphragm.The stress change is decreasing slowly and then increasing rapidly from the center to the edge of the diaphragm along radial direction.（2）When structure size and the load are same,among the four available diaphragm materials of Inconel X-750,Inconel 600,3J53 and Al₂O₃ ceramics,the deflection changes of Inconel X-750 and Inconel 600 are similar,while the deflection at center of Al₂O₃ ceramic diaphragm is minimum.The maximum stress value of Inconel X-750,Inconel 600 and 3J53 are approximative,while the stress value of Al₂O₃ ceramic diaphragm is apparently higher than the other three,and its stress increase rate is faster with the increase of the uniform load.（3）When material of pressure sensing diaphragm and the uniform load are same and the diaphragm diameter is constant,its central deflection as well as maximum stress of the diaphragm decreases gradually with thickness increase of the diaphragm.When the thickness of the diaphragm is constant,the center deflection of the diaphragm as well as maximum stress gradually increases under the same uniform load with the diameter increase of the pressure sensing diaphragm.The maximum stress value of the two diaphragms with structure size of 28mm-20μm and 42mm-35μm are relatively close,and the mechanical properties are identical.When the uniform load is higher than 200Pa,the maximum deflection of the 28mm-20μm diaphragm is about 71%of the 42mm-35μm diaphragm.（4）The impact of pre-tension on the pressure sensing diaphragm deflection is distinct.The deflection decreases with the increase of pre-tension.With the increase of the uniform load and the pre-tension,the change rate of diaphragm deflection decreases and the decline extent recedes.Under the same uniform load,the larger the pre-tension is,the larger the impact ratio is.However,with the continuous increase of the uniform load and the diaphragm deflection,the deflection change caused by pre-tension is weakening,and the impact extent also slows down.（5）ANSYS Workbench can be used to analyze mechanical properties of the capacitive diaphragm vacuum gauge pressure sensitive diaphragm effectively.The simulation values are consistent with theoretical calculation val ues.The reliability of numerical model and feasibility of the software applied in the simulation of the pressure sensing diaphragm of the capacitive diaphragm vacuum gauge are further verified through prototype test.The simulation calculation has certain theoretical guidance and reference for the real product design.