AVS2001 Session VST1-ThP: Pressure Measurement & Calibration Poster Session

Thursday, November 1, 2001 5:30 PM in Room 134/135
Thursday Afternoon

Time Period ThP Sessions | Topic VST Sessions | Time Periods | Topics | AVS2001 Schedule

VST1-ThP-1 A Constant Volume Flowmeter for Calibrating Mass Flow Meters
D. Tian, X. Wen (Lanzhou Institute of Physics, P.R. China)
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 10-3~100 Pam3/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.
VST1-ThP-3 Calibration Apparatus of Mass Spectrometer for Partial Pressure Analysis using Dynamic Flow Method
D. Li, Z. Li, F. Yan, D. Zhang, J. Zhang, H. Xu, Y. Gong, L. Li (LanZhou Institute of Physics, P.R. China)
In order to solve the problem of calibration of mass spectrometer, we had designed and made the calibration apparatus of mass spectrometer for partial pressure analysis using dynamic flow method, which had the ability to calibrate all kinds of mass spectrometer. The calibration apparatus was composed of the source system of gas, the inlet system of gas, the chamber of calibration, the pumping system, the collecting and processing system of data. To gain the accurate measure of partial pressure,we adopted spin rotary gauge(SRG) as the measure standard.the measurement range is 10 -1 to 10-6Pa. There were three independent source and inlet systems of gas in the same structure in the calibration apparatus. Gas brought from anyone of three independent source and inlet systems of gas can produce a partial pressure ranged from 10-1to 10-6Pa. Thus, it not only provides the basic for calibrating, but also is easier to calibrate. To acquire the well-distributed molecular flow in the chamber of calibrating, the spherical chamber of calibrating is 350mm in diameter. On the basic symmetry principle, the normal of the equator plane on which seven CF35 and a CF63 were mounted on the spherical chamber was aligned with the boresights of the inlet aperture and the outlet aperture to the chamber, so that SRG and calibrated mass spectrometer located in the same condition. To realize automatic collecting and processing of data, we have applied the computer technology .the software designed on our own is convenient for user. the main technical data is: Ultimate pressure: 5×10-7Pa Calibration range: 10-1 to 10-6Pa uncertainty: ≤4.8% Calibrated gas: 1 to 3 different gas The calibration apparatus can be used for calibration of sensitive,linearity,stability ,etc of mass spectrometer.
VST1-ThP-4 The Role of Viscosity Parameter in the Calibration of a Spinning Rotor Gauge
P. Mohan (National Physical Laboratory, (NPL), India)
Spinning rotor gauges (SRGs) act as transfer standards for measurement of pressures in the range 1 Pa to 10-4 Pa. There are two methods for the measurement of the gauge calibration factor. In the first, the gauge is connected on a primary standard and pressures in the range 0.1 to 1 Pa are generated and the viscosity parameter is entered as equal to zero in the gauge controller. Then a plot of the ratio of indicated pressure to the real pressure ( =σeff) against the real pressure is obtained as a line with negative slope. The intercept of this plot for the real pressure equal to zero gives the gauge coefficient. In the second method, the same procedure is adopted but the actual value of the viscosity of the test gas is entered into the controller. The plot obtained in this case is a horizontal line. The average of the different σeff values gives the gauge coefficient. This paper gives the results obtained at the National Physical Laboratory (N. Delhi)for the calibration of three SRGs by the two methods and shows that agreement of ±0.1 % is obtained in all the three cases.The real pressures were generated using the NPL primary standard based on the principle of static expansion.
VST1-ThP-5 Primary and Secondary Vacuum Standards Based on Piston-cylinder Technique
J. Tesar, D. Prazak (Czech Metrology Institute, Czech Republic)
In the last years there were developed vacuum standards based on the piston principle with several construction designs. They can be utilised both in primary and in secondary metrology of vacuum. Covered ranges start at atmospheric pressure and reach the tenths of pascal. The attainable accuracy of top standards is fully comparable with other physical principles (mercury columns, static expansion, CDG). The first part of this paper will briefly summarize the most important construction designs, including ranges and attainable uncertainties. The second part of presentation will describe basic primary methods of calculation of effective area from dimensional measurement for classical, non-rotating, divider and conical design of primary piston standards of vacuum. In the third part the basic methods of secondary traceability will be shown: direct comparison with a liquid column standard, direct comparison with a static expansion system and three types of cross-floating comparisons in absolute pressure mode. Description of every method will be supplemented by a typical example from CMI praxis including full uncertainty budget.
VST1-ThP-6 Clamshell Leak Testing Tools
J.C. Brunet (CERN-now retired, Switzerland); P. Coly, P. Cruikshank, M. Duret, M. Genet, A. Jacquemod, N. Kos, H. Nemoz (CERN, Switzerland); P. Trabujo (SGS Qualitest, France)
The Large Hadron Collider (LHC) is the next accelerator being constructed at CERN. Over 40000 in-situ welds will be performed on the helium and vacuum systems in the LHC tunnel. Elastomer clamshell tools have been developed to permit high sensitivity leak testing of welded tubular connections using the so-called "hood" technique. The application, design and peformance of the clamshell tool will be described.
VST1-ThP-7 Pressure Leak Calibration Apparatus
D. Zhang (Chinese Vacuum Metrology Center, P.R. China)
Pressure Leak Calibration Apparatus is a metrology standard for calibrating gas leak rate and has been used to calibrate the pressure leak. Pressure leak is a kind of instrument, on the condition of defined temperature and inlet pressure (more than one atmosphere), to offer known leak rate to one atmosphere side. The pressure leak apparatus is composed of the system of constant volume method and the system of dynamic comparison method with quantitative gas. In the constant volume method, the pressure of constant volume is measured by absolute pressure method and differential pressure method, which both expends the lower limit and upper limit of measurement. In the dynamic comparison method with quantitative gas, the problem of verifying the unknown trace gas is solved with quantitative method. The sample of mixed gas and quantitative gas are produced with pressure reduction method and the gas introduced respectively into mass spectrum chamber with molecular flow method is analyzed by mass spectrum. With such technique, the repeatability is guaranteed. And the lower limit is expended for 2 orders and the small leak rate accordingly can be calibrated. The pressure leak can be calibrated with these two methods, respectively. In the multiple range of both the constant volume method and the dynamic comparison method with quantitative gas, there is satisfactory agreement. The range of constant volume method is from 1¡Á102to 5¡Á10-3PaL/s, uncertainty is from 2.6% to 9.1%£»the range of dynamic comparison method with quantitative gas is from 2¡Á10-2 to 5¡Á10-5Pa L/s, uncertainty less than 14.2%.
VST1-ThP-8 The Study of Leak Detection for Multi-systems with Mass Spectrometer
Y. Rongxin (BeiJing Spacecraft, P.R.C)
The apparatus of leak detection for multi-systems with mass spectrometer is consisted of the leak detection cumulating vessel, sampling cycle system, beginning gas cumulating vessel, pressuring gas equipment, leak rate calibration equipment. The multi-systems pressured different inert gas were put into the leak detection cumulating vessel and the leak detection cumulating vessel was sealed in the air environment. The gas in the leak detection cumulating vessel was pumped into the beginning gas cumulating vessel. After the multi-systems put into the leak detection cumulating vessel, the gas in the leak detection cumulating vessel was forced to uniform. The gas of the leak detection cumulating vessel and the beginning gas cumulating vessel was alternatively analyzed by the mass spectrometer and the ion currents was accordingly got. The calibrating gas was injected into the leak detection cumulating vessel. The gas of the leak detection cumulating vessel and the beginning gas was alternatively analyzed again. The leak rates of multi-systems were calculated. The search gas of different time in leak detection cumulating vessel was comparatively measured with beginning gas stored in the beginning gas cumulating vessel. Therefore, the problem of repeat and reliability of quadpole mass spectrometer in long time was avoided. The problem of quadpole mass spectrometer calibration was avoided by injecting the quantitative calibration search gas into the leak detection cumulating vessel. The ion current of calibration search gas and the ion current of end gas were the same level by controlling the quantity of injecting the quantitative calibration search gas. The problem of the linearity of quadpole mass spectrometer also was avoided.
VST1-ThP-10 A Compact Leak Rate Calibration System
X. Chen, Q. Zhang, Q. Liu, F. Yang, L. Cha (Tsinghua University, P.R. China)
A compact leak rate calibration system has been developed to meet the quality control of industrial leak detection, especially the growing needs of sniffing application. It was designed to calibrate the leak rate from high pressure to atmosphere (pressure leak), but can be used for vacuum leak (from atmosphere to vacuum) rate calibration also. A new method based on constant volume change in pressure for pressure leak rate calibration has been put forward. A differential capacitance diaphragm gauge (CDG) has been selected to decrease the temperature effect greatly. The system consists of a calibration unit and a computer. All of the data could be collected and processed automatically. A mechanical pump has to be added if the system is used for calibrating vacuum leak rate. The whole size of the calibration unit is 30 X 20 X 20 cm3 only. The main parts of the calibration unit are: 1. a reference chamber with a valve connected to atmosphere or a vacuum pump; 2. a calibration chamber with a valve connected with the calibrated leak; 3. a differential CDG; 4. an isolate valve between the above two chambers for pressure balance before calibration or turn on the test, the total valium of the reference region has been pre-calibrated and the calibration region including the outlet of the test leak can be calibrated by the system itself; 5. a temperature monitor unit; 6. an heat isolator system. It was proven that 1 X 10-5 Pam3/s pressure leak rate at room temperature could be calibrated with an accuracy of better than ±5% ( the confidential index is 95% ) and the minimum pressure leak rate could be calibrated was 3 X 10-6 Pam3/s with an accuracy of better than ±15% , when the environmental temperature change was within ±0.1°C. The total test period was about 30 minutes. The system is compact and suitable for leak rate calibration in industry.
Time Period ThP Sessions | Topic VST Sessions | Time Periods | Topics | AVS2001 Schedule