IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Vacuum Science & Technology Thursday Sessions
       Session VST1-ThP

Paper VST1-ThP1
A Constant Volume Flowmeter for Calibrating Mass Flow Meters

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Pressure Measurement & Calibration Poster Session
Presenter: X. Wen, Lanzhou Institute of Physics, P.R. China
Authors: D. Tian, Lanzhou Institute of Physics, P.R. China
X. Wen, Lanzhou Institute of Physics, P.R. China
Correspondent: Click to Email
The mass flow meters are used almost exclusively in the semiconductor industry for the admission of process gases. While they have been used in the semiconductor industry for over twenty years, their performance still remains to be understood about gas factor, orientation, pressure, and temperature effects. Therefore, the mass flow meters need to be calibrated so as to reduce the systematic errors and improve their interchangeability and reliability. In order to calibrate the mass flow meters, a constant volume flowmeter was made in Lanzhou Institute of Physics (LIP). The principle of the flowmeter is to measure pressure change rate with constant volume. The flow is the product of volume and pressure change rate. The vacuum system is all made of metal. The calibration chamber, whose inner surface is treated by electric-chemical polishing, is cylinder-shaped with stainless steel. Rotary pump, which is used to evacuate the chamber, is the main pump of this system. The gravimetric and gas expansion methods are used to measure the chamber volume precisely. The pressure, time interval, and temperature are measured by a high accurate capacitance diaphragm gauge (CDG), a quartz oscillator and a platinum resistance thermometer, respectively. The apparatus is controlled by computer to fulfill the automatic operation and avoid the effect from operators. Constant volume method is a powerful method for calibrating the mass flow meters. There are many disturbing factors in this method, such as change of temperature, adsorption, outgassing, leak, etc. These factors are considered during the design of this apparatus and confined to reasonable scope. The range of the flowmeter is 10@super -3@~100 Pam@super 3@/s (1 sccm~50 slm) with uncertainty less than 1.2%. The main sources of uncertainty are pressure measurement and the temperature change. The uncertainty can be lowered by making a study of the CDG's property and decreasing the vibration of temperature.