Research On Capacitive Diaphragm Gauge And Its Related Technology

Vacuum measurement technology is an important part of vacuum science and technology,the field of national defense and people’s livelihood have put forward higher requirements for vacuum measurement technology,and accurate measurement of vacuum is particularly important.Capacitance diaphragm gauge has a series of advantages such as small size,light weight,high measurement accuracy,good linearity,fast dynamic response,being able to measure the full pressure of gas and steam,and the measurement results are independent of gas composition.It is widely used in nuclear physics,semiconductors,aerospace,high-end equipment manufacturing and other industrial research fields.At present,the development of capacitance diaphragm gauge in China is not mature enough compared with foreign countries.Therefore,it is urgent to carry out the independent development of capacitance diaphragm gauge in order to realize the independent control of the core vacuum instruments.In this paper,the related technologies in the design process of capacitance diaphragm gauge sensors was studied.The factors affecting the linearity and sensitivity of capacitive diaphragm gauge were studied by theoretical analysis and simulation.The temperature compensation method of capacitance diaphragm gauge was proposed.The thermal structure coupling analysis and modal analysis of capacitance diaphragm gauge were carried out based on the finite element analysis software.The main work is as follows.(1)Theoretical model for the deformation of circular and square pressuresensitive diaphragm and capacitance calculation of capacitance diaphragm gauge were constructed.Based on the deformation model of the elastic sheet in elasticity,the solution of the circular film and the square film with clamped edges under large deflection and small deflection deformation were deduced,and the deflection solution of the pretensioned circular film was introduced.The deformation results of large deflection and small deflection of the circular film were compared and analyzed which provides a theoretical basis for the structural design of pressure-sensitive membrane,which provides a theoretical basis for the structural design of the pressure-sensitive diaphragm.Based on the calculation principle of the capacitance of the parallel plate capacitor,the calculation formulas of the initial capacitance and variable capacitance of the capacitance diaphragm gauge were analyzed and deduced,which provides a theoretical basis for the research on the output characteristics of the capacitance diaphragm gauge.(2)The factors that affect the linearity and sensitivity of capacitance diaphragm gauge were analyzed,and its inherent influence rules were found.The influence of the structure of the pressure-sensitive diaphragm,including its shape(circular,square and rectangular),structural parameters(area and thickness)and structural forms(flat film and island film),material of the pressure-sensitive diaphragm,pretension of pressuresensitive diaphragm,fixed electrode structure and electrode spacing,and the working mode of the sensor on the linearity and sensitivity of the capacitive diaphragm gauge are analyzed.The structure of the pressure-sensitive diaphragm suitable for the capacitive diaphragm gauge was given.(3)The zero-point thermal drift temperature compensation method and thermal structure coupling analysis of capacitance diaphragm gauge were completed.A simplified sensor zero-point thermal drift model was established.The influence of temperature on the zero-point thermal drift of capacitance diaphragm gauge was studied,and the causes of the temperature drift of capacitance diaphragm gauge were analyzed.Then,the temperature compensation method of capacitance diaphragm gauge was proposed,and the overall model of the capacitance diaphragm gauge was established,and the temperature field and stress field distribution were analyzed.The results show that the structural characteristics of the pressure-sensitive diaphragm,the thermal expansion of each component and the small electrode spacing are the main reasons for the zero-point thermal drift.It takes at least 5 hours to heat capacitance diaphragm gauge from room temperature to 45°C.The temperature distribution of capacitance diaphragm gauge has good consistency during constant temperature heating,and the maximum stress is 62.8 MPa,which meets the working requirements.(4)Capacitance diaphragm gauge pressure-sensitive diaphragm and overall modal analysis were carried out.Based on the capacitance diaphragm gauge geometric model established by the thermal structure coupling analysis,the modal analysis was carried out for the pressure-sensitive diaphragm under different pretensions,the capacitance diaphragm gauge with insulation cavity and without insulation cavity.The corresponding inherent frequencies and vibration modes were obtained.The theoretical solution of the natural frequency of the pressure-sensitive diaphragm is in good agreement with the simulation solution,which verifies the reliability of the simulation model.The results of the simulation have a certain guiding significance for the design of actual products.