UNCERTAINTY EVALUATION OF CALIBRATING EXTREMELY LOW LEAK RATE WITH STATIC EXPANSION TECHNIQUE

An extremely low leak rate calibration method based on static expansion technique has been used to calibrate a vacuum leak of 10^-10Pa·m³/s.It was found the measurement uncertainty mainly comes from the rise rate of ion current about the leakage.Compared with the uncertainty components of three stages expansion method with high purity gases,two stages expansion method with gas mixture can ameliorate the calibration results by avoiding complex expansion process,which simplified the calibration process and improved the calibration efficiency also.