| 摘要 |
A counterflow helium mass spectrometer leak detector includes a test port for receiving a gas sample including the tracer gas helium, a high vacuum pump such as a diffusion pump and a mass spectrometer tuned to detect the helium. The mass spectrometer is coupled to the inlet of the high vacuum pump. The leak detector further includes a cold trap containing liquid nitrogen coupled between the test port and the foreline, or outlet port, of the high vacuum pump. The helium received at the test port passes in reverse, or counterflow, direction through the high vacuum pump to the mass spectrometer. One or more mechanical vacuum pumps insure that the pressure at the foreline of the high vacuum pump is maintained at a prescribed level during a leak test. The cold trap condenses contaminants, water vapor and other gases from the gas sample and prevents backstreaming of oil from mechanical vacuum pumps. |
