A brief review of the stagnation history of normative leaks and normative leak calibration steps
Standard leaks As early as 1963, Tsinghua University developed a glass 2 platinum wire type standard leak, and continued to study its cyclonic characteristics. Glass 2 platinum wire type standard leaks are made by using platinum wire and hard glass with the opposite shrinkage coefficient, and they continue to be unmatched. The test confirms that the practical relationship between the leakage rate of such leaks and the outlet pressure, the size and size of the leaks, the heat of the conditions, and the test gas is wrong. The leakage time of this leak is less than 0.5s, and the thermal coefficient of the leak rate is much smaller than that of the helium-permeability norm of the film, and it can be easily modified. If the leak is blocked by steam, baking can be continued under the condition that both ends of the leak are evacuated at the same time, so that the leak can be restored. When the platinum wire diameter is 0.10 ～ 0.15mm, the sealing length is 5 ～ 10mm, and the outlet pressure is an atmospheric pressure, the leakage rate of 10-6 ～ 10-8Pa & middot; m3 / s can be lost. The leakage rate of this type of leak has a linear relationship with the pressure difference between the two ends of the leak. If the pressure at the outlet end is increased, the leak rate of the leak will also increase linearly. Therefore, this leak is a molecular flow leak, which can be used as an adjustable leak to continue real-time calibration over a wide static scale. Utilizing this leak hole can realize the calibration of ultra-high-sensitivity leak detection.
In 1964, Tsinghua University continued to study the helium permeation type leaks in the film. For a large number of quartz, the penetration power of helium is greater than that of other gases. The helium leakage type current limiting element is a spherical ground film made of quartz blowing, and its thickness is about 0.05 ~ 0.20mm. The helium permeability of a helium-permeable leak has nothing to do with the thickness of the quartz film, the infiltration area, and the helium pressure charged. By choosing the opposite thickness of the quartz film, the infiltration area, and the helium pressure to inject, it can make a standard leak with the opposite leakage value Porosity and leakage rate are usually between 10-8 ～ 10-11Pa & middot; m3 / s. This type of leak is still the most common leak for calibrating helium mass spectrometers. It has the advantages of anti-purification, anti-blocking, and stable performance. However, the quartz mulch is fragile, so that it is not acceptable to be impacted. It should be used with special care. Recently, some people have continued to improve the manufacturing process of this type of standard leak.
Calibration of standardized leaks In China, calibration of standardized leaks began in the 1960s. In 1963, when Tsinghua University developed a glass 2 platinum wire type standard leak, a calibration procedure for the standard leak was proposed. According to the conditions, the constant volume method is adopted to calibrate the standard leak. The pressure change is measured by a compression type vacuum gauge. The standard calibration scale for the standard leak calibration is 10-7 ~ 10-9Pa & middot; m3 / s. In the following 30 years, the constant volume method has been adopted to calibrate the standard leak. In 1966, Fan Lei and others constructed a standard leak calibration calibration piece, using a hot negative electrode hydrolytic gauge to measure the pressure change. The calibration scale of the calibration piece was 10-6 ~ 10-8Pa & middot; m3 / s, with an uncertainty of 25%. In 1978, Xie Tongfu and others built a standardized leak calibration system that adopted the B2A gauge to measure pressure changes. The calibration scale of the calibration system was 10-510-12Pa & middot; m3 / s, with an uncertainty of 23%. In 1983, the standard leak constructed by Hu Yaozhi and others was calibrated and the pressure was measured with a B2A gauge. The fragment is equipped with a suction suction pump & mdash; The 10-10Pa & middot; m3 / s scale calibrated the helium permeation leaks of the membrane with its own air chamber. The results show that the calibration accuracy is within 5%.
Later, the helium mass spectrometer analog method was also used to calibrate the leak. This step is extremely easy. It is to perform leak calibration by comparing leaks with known leak rates and helium peak signals generated by a calibrated leak on a helium mass spectrometer. At the age of 90 in the 20th century, China ended its commitment to the development of high-precision standardized leak calibration installation. In 1994, Lanzhou Institute of Physics Research and Development successfully developed a constant pressure gas micro-flow meter with a flow measurement scale of 2 & times; 10-2 ～ 1 & times; 10-8Pa & middot; m3 / s, with an uncertainty of 2%. It is used to calibrate the standard leak. The calibration is continued by comparing the ion leak signal of a certain gas generated on a quadrupole mass spectrometer with that of a calibrated leak and a gas microflow meter. The leakage rate of the leak hole is very similar or imminent, and the non-linearity of the quadrupole mass spectrometer can be increased. According to the measurement scale of the flow meter, when the leak rate of the calibrated leak hole is less than 1 & times; 10-8Pa & middot; m3 / s, it is necessary to consider the uncertainty caused by the nonlinearity of the quadrupole mass spectrometer. The calibrated leak rate scale of this installation is 2 & times; 10-2 ~ 1 & times; 10-10Pa & middot; m3 / s.
In 1997, China Metrology Superstition Research Institute developed a constant volume gas micro-flow meter to regulate the calibration of leaks. The fixed-capacity gas micro-flow meter has a measurement scale of 2 & times; 10-4 ～ 1 & times; 10-6Pa & middot; m3 / s, with an uncertainty of less than 1.5%; after adopting the flow calibration method, the upper limit of the leak rate calibration scale can spread to 5 & times; 10-9Pa & middot; m3 / s, uncertainty is less than 9.0%. Leak calibration is also continued by comparing the ion leak signal of a certain gas generated on a quadrupole mass spectrometer with a calibrated leak and a gas microflow meter, but this step fundamentally prevents the non-linearity of the quadrupole mass spectrometer. The resulting uncertainty.
In terms of leak rate specifications, from 1998 to 1999, China Metrology and Superstition Institute of Lanzhou and Lanzhou Institute of Physics continued to compare the leak rate specifications at home, using some standard leaks on the order of 10-8 Pa & middot; m3 / s as transmission specifications. The deviation of the unilateral leak rate specification is 3%. In 2002, the leak rate specifications of Lanzhou Institute of Physics and German PTB continued the informal bilateral domestic comparison, and the transmission specifications adopted the helium permeation type leak hole of the film produced in China. The consequence showed that the deviation was 5.6%.
Since the 1990s, due to the extraordinary needs of the aerospace light industry, the calibration of positive pressure leaks has also become a focus of attention in China. In China, the first method to calibrate the positive pressure leak using the drainage gas extraction method is easy, but the calibration time and accuracy are poor. In 1996, Tsinghua University proposed three difficult calibration steps: the first step is a modified drainage gas extraction method; the second step is a pressure vessel test method for measuring the relative pressure difference with a silicone oil-filled U-shaped tube pressure gauge; The three steps are the constant volume method using a differential pressure storage capacity mulch gauge. This step was further improved in 2001 and became a more practical positive pressure leak calibration step. This step is performed by measuring the change in pressure difference. It is necessary to reduce the temperature stability and achieve the positive pressure leak calibration. The installation calibration scale is 1 & times; 10-5 ～ 3 & times; 10-6Pa & middot; m3 / s, the corresponding uncertainty is 5% ～ 15% (the confidence is 95%), and the calibration time is about 30min. In 2001, the positive pressure leak calibration and installation developed by Lanzhou Physics Research Institute adopted the constant volume method and quantitative gas static comparison method to continue the calibration of the positive pressure leak. The constant volume calibration scale is 1 & times; 10-1 ～ 5 & times; 10- 6Pa & middot; m3 / s, its measurement uncertainty is 2.6% ~ 9.1%; quantitative calibration scale of static static method is 2 & times; 10-5 ～ 5 & times; 10-8Pa & middot; m3 / s, its measurement uncertainty is less than 14% .