Performance Test And Real Time Calibration On Ultra-sensitive Leak Detection System

The real-time calibration of the ultra-sensitive leak detection system was carriedby the calibration system basing the results of testing the performance of theultra-sensitive leak detection system and it's calibration system. This subject hasstrong application background, and it is a key technique to guarantee theperformance and long life of small volume vacuum device, and also is an advancedsubject in extreme high vacuum field. There are not lots of research works on theultra-sensitive leak detection lower than 1×10^-13Pa·m³/s magnitude all over theworld. The real time calibration is even a puzzle to be solved and standardized in theworld. The main results of the thesis are:1.Testing the performance of the ultra-sensitive leak detection system, studyingthe helium background and it's influence factors, and maintaining the system in thebest work state by a good background-preserving method found in thesis research.Meanwhile, the other works was carried as follow, testing the sensitivity of thesystem in dynamic mode and accumulation mode, exploring how to improve andpreserve the limit sensitivity in a long term, and testing some real leaks with a verylow leak rate.2. Testing the ion current value of the helium permeation type reference leakequipped to the ultra-sensitive leak detection system under dynamic mode and theion current increase slope value under static accumulation mode. It is found that theslope value is not stable that it influences greatly the quantitative analysis of leakdetection results. Its mean value was gotten by many tests to establish the base oflinear extrapolation. It is pointed out the disadvantages of calibrating theultra-sensitive leak detection system by a leak with the fixed leak rate.3.Realizing the real time calibration of the ultra-sensitive leak detection systemis the main works of the thesis. It has been studied in detail the real time calibrationby the variable reference leak rate system. The ultra sensitive leak detection systemwas calibrated in the leak rate range from 10^-12 Pa·m³/s to 10^-10 Pa·m³/s using thepure helium gas and a commercial leak detector. Specially, the He and N2concentrations were tested after the 1%He-99%N2 gas entered the system, and thereal time calibration was carried successfully in a leak rate range from 10-14 Pa·m3/sto 10-12 Pa·m3/s using the 1% He-99% N2 gas and the variable reference leak ratesystem. It has been proven that the linear extrapolation is still effective in theprevious mentioned leak rate range.4. In order to calibrate the ultra-sensitive system in lower leak rate range, thereal time calibration was carried in a leak rate range from 10-16Pa·m3/s to 10-14Pa·m3/s using the gas containing 100ppm He concentration. The experimental resultsshow that the linear extrapolation is not effect any more when the leak rate is near10-16Pa·m3/s. Meantime, it has been proven that the variable reference leak ratesystem can provide stably the linear and variable leak rate lower to10-15 Pa·m3/s.