Research On Multiphysics Of Dual-Capacitance Diaphragm Gauge

Vacuum measurement technology is an integral component of the modern scientific system and finds widespread applications across various domains,including industry and people’s livelihood.Vacuum measurement instruments are the main manifestation of this technology.Among various vacuum measurement instruments,capacitance diaphragm gauge is conventional vacuum-measuring gauge,that possesses numerous advantages of light weight,small volume,high measurement accuracy,excellent linearity,fast dynamic response,and the ability to measure the gas full pressure without being limited by the gas type.It’s commonly used in space exploration,scientific research,chemical manufacturing,electronic equipment production and other fields.With the development of science and technology,the needs of relevant industries for vacuum-measuring instruments are also gradually increasing.To optimize the capacitance output stability and accuracy of the capacitance diaphragm gauge,the relevant factors including the structure form and diaphragm state of the dualcapacitance diaphragm gauge were studied by combining theoretical analysis,simulation and experiments.The main work is as follows:(1)The basic structure and working principles of the dual-capacitance diaphragm gauge were clarified,and the deformation model of the circular pressure-sensitive diaphragm and the capacitance induction model of the capacitance diaphragm gauge were constructed.Based on the deformation theory of elastic mechanics,the theoretical formulae for calculating the deflection of circular diaphragm in distinguishing large and small deflections were derived,and the theoretical formulae for calculating the deflection of circular pressure-sensitive diaphragm under pre-tension were derived;Based on the capacitance calculation theory of parallel plate capacitor,the theoretical calculation formulae for measuring capacitance and reference capacitance were derived.It provides a theoretical basis for the study of the capacitance output characteristics of the dual-capacitance diaphragm gauge.(2)Based on COMSOL software,the capacitance induction model of singularcapacitance diaphragm gauge and dual-capacitance diaphragm gauge were established.The factors affecting the capacitance output characteristics of the capacitance diaphragm gauge were analyzed,and their influence mechanism was studied,including the structure of the fixed electrode plate,the frame,the gap between movable and fixed electrodes,and the pressure-sensitive diaphragm materials.The results showed that the capacitance output stability of the dual-capacitance diaphragm gauge was better,the linearity increased by 1% for 1 Torr,3.6% for 100 Torr,0.6% for 1000 Torr;The frame would bring additional capacitance,but the impact on dual-capacitance diaphragm gauge was approximately 50% smaller than that on singular-capacitance diaphragm gauge;With the increase of the gap between movable and fixed electrodes,the capacitance output sensitivity of the vacuum gauge decreased and the linearity increased;When using 3J53 constant-modulus alloy as the pressure-sensitive diaphragm material,the capacitance output characteristic of the vacuum gauge was better.(3)The capacitance output of capacitance diaphragm gauges with different specifications at room temperature was analyzed through experiments.Utilizing the experimental debugging platform of the capacitance diaphragm gauge,the capacitance output of the capacitance diaphragm gauge was measured.Compared with the simulated results,the relative error was approximately 20%;The capacitance diaphragm gauges with different structures were measured,and the dual-capacitance diaphragm gauge exhibited better linearity by comparison,the linearity increased by 3.9% for 1000 Torr,0.6% for 10 Torr;The capacitance diaphragm gauges with different thicknesses of pressure-sensitive diaphragm were tested,demonstrating that the capacitance output sensitivity decreased and the linearity increased as the thickness of pressure-sensitive diaphragm increased;The capacitance diaphragm gauges with different heat treatment temperatures were tested,demonstrating that the capacitance output sensitivity decreased and the linearity increased as heat treatment temperature increased;Tests were also performed on capacitance diaphragm gauges with pressure-sensitive diaphragm of different materials,and results showed the use of the 3J53 constantmodulus alloy as the pressure-sensitive diaphragm material yielded better capacitance output characteristic,compared with 304 stainless steel,the sensitivity increased by0.0355 p F/Pa for singular-capacitance diaphragm gauge and the linearity increased by1.6%,the sensitivity increased by 0.0044 p F/Pa for dual-capacitance diaphragm gauge and the linearity decreased by 1.4%;Under the conditions of different electrode spacing parameters,the capacitance diaphragm gauges were tested.With the increase of the gap between movable and fixed electrodes,the capacitance output linearity increased and the sensitivity decreased,along with an increase in the vacuum gauge’s measurement range.