Fabrication,Testing And Application Of The Large Flow Constant Conductance Element

Constant conductance elements are increasingly used in vacuum leak detection and vacuum metering,while existing constant conductance element can only provide a small flow rate while maintaining molecular flow,which limits the measurement of constant conductance element in pump speed.In view of the problems existing in traditional constant conductance elements,this paper proposes a fabrication scheme for large constant conductance elements.Anodic aluminum oxide(abbreviated as AAO)has densely arranged nano-sized pores with hexagonal distribution.By increasing the effective area of AAO,a large flow of molecular flow constant conductance elements can be obtained.An AAO constant conductance element with a specific effective area was prepared by using an anodic aluminum oxide as a template and a silicon wafer-AAO-oxygen-free copper plate "sandwich" structure.Based on the dynamic differential pressure decay method,the measurement system is designed and built independently.Two fixed containers are connected at both ends of the AAO.The dynamic differential pressure changes at both ends of the element are exponentially related to the volume of the container,the conductance of AAO and the time.By measuring the dynamic differential pressure decay at both ends of the AAO,the conductance of the constant conductance element AAO is calculated,and then the transient mass flow rate is calculated.A pump speed measuring system was set up to measure the pumping speed of the diaphragm pump(model Pfeiffer TSU 071 E).The results show that with nitrogen,helium and argon as experimental gases,the conductance of the constant conductance elements is constant,and does not change with the differential pressure at the two ends and the pressure of the front stage,which is consistent with the molecular flow characteristics;The mass flow rate of a gas through a constant conductance element decays exponentially with time;In the measurement of pump speed,the known flow rate is obtained by changing the pressure of the front stage,and the measured result of pump speed is consistent with the pumping speed curve in the manual,which verifies the effectiveness of the method.The large flow constant conductance element of AAO proposed in this paper has a simple manufacturing process and low cost,and can obtain a large flow of molecular flow element according to requirements,also it can accurately measure the pump speed.